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Basin Bridge Project

Technical Report 1 - Design Philosophy Statement

Basin Bridge Project

Technical Report 01 -

Design Philosophy

Statement

© Opus International Consultants Ltd 2013

Revision Schedule

Rev. Date Description Prepared by Reviewed by Approved by

1 March 2012 For Draft SAR Sam Thornton Gareth McKay Gareth McKay

2 10 August 2012 For Planning Review Sam Thornton Gareth McKay Gareth McKay

3 3 December 2012 For Planning Review Gareth McKay Sam Thornton Gareth McKay

4 15 March 2013 For AEE Sam Thornton Wayne Stewart Wayne Stewart

5 5 June 2013 For Lodgement Sam Thornton Wayne Stewart Wayne Stewart

Prepared By Opus International Consultants Ltd

Sam Thornton, Design Manager Wellington Civil

Peter Jones, Lighting L7, Majestic Centre, 100 Willis St

Neil Jamieson, Wind PO Box 12 003, Wellington 6144

Pathmanathan Brabhaharan, Geotech New Zealand

Telephone: +64 4 471 7000

Reviewed By and

Approved for

Release By

Facsimile: +64 4 471 1397

Wayne Stewart

Team Leader Date: 5 June 2013

Reference:

Status: For Lodgement

Basin Bridge Project – Technical Report 1: Design Philosophy Statement i

| 5 June 2013 Opus International Consultants Ltd

Contents

1 Introduction ........................................................................................................1

2 Project Description ............................................................................................ 2

2.1 Transport Improvements...................................................................................................... 3

2.2 Urban Design and Landscape ............................................................................................... 5

2.3 Related Projects ..................................................................................................................... 8

3 Geometric Design ............................................................................................... 9

3.1 Constraints Governing the Design ....................................................................................... 9

3.2 Design Speed ........................................................................................................................ 12

3.3 Design Standards ................................................................................................................. 13

3.4 Road Design Cross Sections ................................................................................................16

4 Signs and Markings .......................................................................................... 20

4.1 Traffic Signs and Pavement Markings ............................................................................... 20

5 Traffic Signals and Intelligent Traffic Systems ................................................. 22

5.1 Traffic Signals Design ......................................................................................................... 22

5.2 Intelligent Traffic Systems (ITS) ........................................................................................ 22

6 Transportation Design ..................................................................................... 24

6.1 Existing Pedestrian and Cyclist Facilities .......................................................................... 24

6.2 Pedestrian and Cyclist Options Considered ...................................................................... 24

6.3 Local Road Changes (including Bus Lanes) ...................................................................... 35

6.4 Parking Design .................................................................................................................... 40

6.5 Schools Drop-off Area ..........................................................................................................41

7 Geotechnical Engineering ................................................................................ 42

7.1 Introduction ......................................................................................................................... 42

7.2 Geology................................................................................................................................. 42

7.3 Site Investigations ............................................................................................................... 44

7.4 Ground Conditions .............................................................................................................. 45

7.5 Seismicity ............................................................................................................................. 46

7.6 Liquefaction Hazard ............................................................................................................ 48

7.7 Summary of key geotechnical issues .................................................................................. 49

7.8 Scope of geotechnical works required................................................................................ 50

7.9 Figures .................................................................................................................................. 55

8 Pavement and Surfacing ................................................................................... 58

8.1 Traffic Assumptions ............................................................................................................ 58

8.2 Pavement Assumptions....................................................................................................... 59

8.3 Pavement Design ................................................................................................................. 59

8.4 Road Surfacing .................................................................................................................... 59

Basin Bridge Project – Technical Report 1: Design Philosophy Statement ii


9 Stormwater .......................................................................................................61

9.1 General Philosophy ..............................................................................................................61

9.2 Design Standards .................................................................................................................61

9.3 Proposed Level of Service ....................................................................................................61

9.4 Design Parameters / Assumptions ..................................................................................... 62

9.5 Construction Stormwater Treatment ................................................................................. 63

10 Structures ........................................................................................................ 64

10.1 Bridge ................................................................................................................................... 64

10.2 Building under the Bridge .................................................................................................. 67

10.3 Basin Reserve Northern Gateway Building ....................................................................... 68

11 Urban and Landscape Design ........................................................................... 69

12 Lighting ............................................................................................................ 70

12.1 Street Lighting ..................................................................................................................... 70

12.2 Design Options Considered ................................................................................................ 70

12.3 Current Design Proposal ...................................................................................................... 71

12.4 Design Outcomes .................................................................................................................. 71

12.5 Architectural Lighting ......................................................................................................... 72

13 Services and Utilities ........................................................................................ 73

14 Noise ................................................................................................................ 76

15 Wind ................................................................................................................. 77

15.1 Existing Wind Conditions ....................................................................................................77

15.2 Effects of the Proposed Scheme on Local Wind Conditions .............................................77

16 Future Proofing ................................................................................................ 80

16.1 Wider Strategy ..................................................................................................................... 80

16.2 Passenger Transportation Spine ........................................................................................ 80

16.3 Inner City Bypass (Karo Drive and Vivian Street) ............................................................ 80

16.4 Mount Victoria Tunnel Duplication ................................................................................... 80

16.5 Intelligent Traffic Systems (ITS) ........................................................................................ 81

Appendix 1.A – Proposed Design Requirements for the Building under the Bridge

Basin Bridge Project Technical Report 1: Design Philosophy Statement 1


1 Introduction

This document provides a summary of the matters that have been considered in the engineering

design of the Project, including geometric design, signs and markings, traffic signals,

transportation design, geotechnical matters, pavement and surfacing, stormwater, structures,

urban and landscape design, lighting, service utilities, noise, wind, and future proofing. Where

relevant, this document indicates the standards on which the Project design is based, decisions that

were made and, where they exist, departures from standards. This document should be read

alongside a number of other documents that describe the current design, including:

• Technical Report 3: Urban and Landscape Design Framework

• Volume 4: Construction Management Plans

• Volume 5: Plan Set

If the Project is consented it will then undergo detailed design and construction. During the

detailed design process (and possibly during construction) it may be necessary to modify and adapt

the design in response to new information that comes to light (including, but not limited to;

unforeseen services and ground conditions, new standards and regulations and cost and

construction efficiencies). However, material departures from the principles and standards

proposed in this document are not expected through the detailed design process.



2 Project Description

The Project proposes to construct, operate and maintain new transport infrastructure for State

Highway 1 at the Basin Reserve. A key component of the proposal is a multi-modal bridge that

connects Paterson Street with Buckle Street. The bridge will provide a two lane one-way

carriageway for SH1 westbound road users and includes a shared walking and cycling path on its

northern side.

Proposed at-grade road improvements include changes to Dufferin Street and sections of Paterson

Street, Rugby Street (including the intersection with Adelaide Road), Sussex Street, Buckle Street

(SH1), Taranaki Street, Vivian Street (SH1), Pirie Street, Cambridge Terrace, Kent Terrace (SH1),

Ellice Street and Hania Street. The overall road layout is shown diagrammatically on Figure 1- 1

below.

Figure 1- 1: Project Area showing the proposed roading layout and land to be designated

The Project also provides urban design and landscape treatments. These include new landscaped

open space areas, a new building under the bridge on the corner of Kent Terrace and Ellice Street, a

new entrance and Northern Gateway Building to the Basin Reserve, an improved streetscape

entrance to Government House and adjacent schools, a modified car park for St Joseph’s Church,

dedicated bus lanes and bus stops around the Basin Reserve, as well as new walking and cycling

paths.



Proposed landscaping and urban design treatments include low level plantings, raingardens, trees,

terracing, architectural bridge design including sculptured piers, furniture and paving. These

measures aim to contribute to the overall integration of the proposed bridge structure into the

surrounding urban environment.

2.1 Transport Improvements

The Project proposes a grade-separated route (the bridge element) for SH1 westbound traffic on

the northern side of the Basin Reserve. As a result, SH1 traffic will be removed from the local road

network around the eastern, southern and western sides of the Basin Reserve.

The bridge soffit will be up to 7.3m above the ground surface and the top of the guard rail will be up

to 10.5m high above the ground. The bridge is approximately 263m long or 320m long if both

abutments are included. It will be supported by six sets of piers (2 are double piers) and six smaller

piers to support the western end of the shared pedestrian and cycleway where it splits away from

the main bridge structure. The bridge has a minimum width of approximately 11.3m and a

maximum width of approximately 16.7m. There are two bridge joins, one at each end.

The Project proposes changes to the SH1 westbound route, the SH1 eastbound route, and other

roads on the network where they connect with SH1, including clearways on the eastern part of SH1

Vivian Street (from Tory Street to Cambridge Terrace). These propose to improve the efficient and

safe movement of traffic (including buses), pedestrians and cyclists through intersections and

provide entry and exit points for SH1. Supplementary works on the existing local road network are

also proposed to be undertaken to take advantage of the additional capacity created by the SH1

improvements.

The Project proposes new pedestrian and cycling routes throughout the Project area as well as

improvements to existing infrastructure. The majority of the works to improve the walking and

cycling routes are located on the north side of the Basin Reserve and connect with Mount Victoria

suburb, Mount Victoria Tunnel and schools on Dufferin Street. These improvements will connect

with the National War Memorial Park which is currently under construction and also with potential

future duplication of Mount Victoria Tunnel.

A reduction in state highway traffic on the roads around the Basin Reserve allows for more efficient

northbound and southbound movements from Kent and Cambridge Terrace to Adelaide Road.

Accordingly, new dedicated bus lanes are proposed to provide for better public transport

movements around the Basin Reserve.

The key traffic flows around the Basin Reserve following the implementation of the proposed

Project are shown in Figure 1- 2 below and described thereafter.



Figure 1- 2: Proposed traffic directions for the Project

The package of transportation improvements proposed by the Project is summarised below and

followed by a brief description of the works:

SH1 westbound (from Mount Victoria Tunnel to Buckle Street)

• The Bridge - new direct link from Paterson Street to Buckle Street via a bridge;

• Buckle Street three laning - provision of third lane along Buckle Street between Sussex Street

(including minor modifications to Sussex Street) and Taranaki Street to improve capacity and

accommodate the two lanes from the bridge; and

• Taranaki Street improvements – modifications to the layout of Taranaki Street and Buckle

Street intersection to accommodate the three laning of Buckle Street and to increase capacity.

SH1 eastbound (from Vivian Street – Kent Terrace - Mount Victoria Tunnel)

• SH1 Eastbound re-alignment - realignment of SH1 eastbound between Hania Street and

Brougham Street; and

• Vivian Street and Pirie Street Improvements – as part of the modifications to the intersection of

Pirie Street and Kent / Cambridge Terraces and Vivian Street, clearways on Vivian Street are

proposed. The combination of improvements increases the capacity of the intersection for all

traffic movements including public transport.

Improvements to roads around the Basin Reserve

• Paterson Street / Dufferin Street intersection – layout modifications to change in priority at the

signals including provision of a significant increase in priority to Dufferin Street (south bound

traffic from Kent Terrace/ Ellice Street);

• Adelaide Road / Rugby Street intersection – reducing through lanes along Rugby Street from 3

lanes to 1 and allowing Adelaide Road traffic and Rugby Street traffic to flow at the same time.



Pedestrian and cycling crossings will be via on-demand signals. Two lanes for access into

Adelaide Road would remain with one operating as a dedicated bus lane;

• Ellice Street link – new road link from Ellice Street to Dufferin Street/Paterson Street

intersection (a similar vehicular movement can currently be made between Ellice Street and

Dufferin Street). A new shared pathway for pedestrians and cyclists would be provided

adjacent to this link to facilitate movements between the Mount Victoria suburb, the schools on

Dufferin Street, and further south toward Adelaide Road;

• Dufferin Street improvements – works to modify the layout of the road space and bus drop off

zones on Dufferin Street and Rugby Street on the south east corner of the Basin Reserve and to

improve vehicular access to Government House; and

• Basin Reserve Gateway – treatment to Buckle Street where it meets Kent/Cambridge Terraces,

and retains an entry point to the re-aligned SH1 eastbound.

Walking, Cycling, Public Transport (throughout the Project Area)

• Walking and cycling path on bridge – new walking and cycling path on the bridge between

Paterson Street and Buckle Street / NWM Park;

• Existing pedestrian and cycle routes – existing at-grade pathways are retained or enhanced and

additional and alternative routes are provided. Additional and improved pedestrian and

cycling access would be provided in the landscaped area on the corner of Cambridge Terrace

and Buckle Street and between Brougham Street and Kent Terrace. These routes link to the

proposed pedestrian and cyclist facilities proposed through NWM Park;

• Public Transport - new dedicated bus lanes are proposed on Ellice Street, Dufferin Street and

Buckle Street, and the southbound bus stop is proposed to be relocated from Adelaide Road

onto Rugby Street; and

• Public Transport - existing priority for buses from Kent Terrace onto Ellice Street is retained.

Detail of the proposed road design layouts are shown in Volume 5: Plan and Drawing Set.

2.2 Urban Design and Landscape

Proposed urban design and landscape treatments to areas outside of the road carriageway form

part of the Project works. The development of the proposed Project design has been iterative,

responsive and collaborative. As such, it has been developed through an Urban Landscape and

Design Framework (refer to Volume 3: Technical Report 2) to address the specific urban design

principles for the Project. The Project proposes treatments to areas adjacent to the road network

that would assist with the integration of the proposed bridge into the surrounding urban context.

Six zones and elements (Zones) for the Project area have been identified within which character

and zone specific principles for those areas have been developed to define the design intent and to

provide a framework for post RMA consenting detailed design development. The zones are shown

on Figure 1- 3 below.



Figure 1- 3: Urban and landscape zones for proposed works outside of the traffic lanes

These are briefly described for the urban and landscape zones below:

Zone 1 Cambridge/Buckle Bridge Interface Zone - proposed landscape treatments to land

between Cambridge Terrace and the NWM Park, which includes rain gardens and wetland

plantings for stormwater treatment. This landscape area has been designed as a continuation of

NWM Park. The terracing in the NWM Park starts from Kent and Cambridge Terraces and are

reflective of the cultural heritage of the area, as cultivation terraces. Wetland planting reflects the

former Waitangi Lagoon which is now the Basin. The landscaping also provides an interface with

the curtilage of the newly relocated Home of Compassion Crèche (former)1.

Zone 2 Kent/Cambridge Basin Gateway: proposed landscaping between Kent/Cambridge

Terrace responds to tangata whenua values in relation to the proposed historical wetland ecology

and provides a safe and enlarged public access and gathering area relative to the Basin Reserve

1 The Home of Compassion Crèche (former) is being relocated as part of the National War Memorial Park project.



entrance. The proposed landscape aims to facilitate gathering and includes reconfigured

pedestrian crossings, bus stops and Basin Reserve entrance.

Element 2.1 Entrance to the Basin Reserve – proposes a combination of planting

(pohutukawa trees) and a new Northern Gateway Building on the northern boundary within the

Basin Reserve. The combination of new Northern Gateway Building and pohutukawa trees screens

the bridge from general views from within the Basin Reserve. The new Northern Gateway Building

is designed to specifically remove potential views of traffic on the bridge from the views of batsmen

(facing bowlers from the north). The new Northern Gateway Building) would provide space for

player facilities and includes a wider entrance for visitors to the Basin Reserve that is aligned with

the new entrance plaza located between Kent and Cambridge Terrace.

The new structure will occupy the space between the RA Vance Stand and the existing toilet block

at the edge of the northern embankment. It will be approximately 65m long and up to 11.2m high

and includes a screen above the existing player’s pavilion between the new building and the RA

Vance Stand. This option is preferred by the Basin Reserve Trust.

Alternative mitigation proposals entail a 45m long structure or a 55m long structure and

consequent increases in proposed tree planting have also been considered and are assessed within

this report.

Zone 3 Kent/Ellice Street corner zone – proposes a new building under the proposed bridge

at the corner of Kent Terrace and Ellice Street which would be made available for commercial use.

It is intended to re-establish the historical built / street edge in this location and the building helps

incorporate the bridge into the built urban environment. A green screen is proposed to be located

above the new building to provide a level of screening for the adjacent apartment building and

assist to visually integrate the bridge with the buildings at this corner.

Zone 4 Paterson/ Ellice/Dufferin Interface zone – proposes to continue ground landscape

linking from across Kent/Cambridge Terraces and additional tree planting around the Basin

Reserve’s outer square.

The Project proposes works within St Joseph’s Church property using land that is currently used

for car parking. Thus, the Project proposes to remove the existing building at 28 Ellice Street and

to adjust the existing car park and provide landscape improvements for the Church within the

remaining space. All of these works are located on land owned by the Church.

Zone 5 Dufferin/Rugby Streets, Schools/Church/Government House Interface zone

which serves as a vehicular and pedestrian access area serving key adjacent land uses of the schools

and Government House. Proposed works include the re-allocation of space in the roading corridor,

layout modification and urban design and landscape treatments.

Zone 6 The Bridge Element – the horizontal alignment of the Bridge has retained a close

reference to the historic street pattern (the Te Aro Grid) to strengthen and define the Basin square.

The vertical alignment has utilised underlying landform to achieve grade separation between

north-south and east west routes. The width of the bridge has been kept to the minimum that

meets safe traffic design standards for a 50km/h road. Abutments are integrated and grounded in

the form and material of the landscaping. Lighting on the bridge seeks to minimise glare and spill

onto surrounding areas and integrates with the bridge form and with the adjacent NWM Park.

Architectural lighting is provided underneath the bridge and across the landscape, highlighting



forms, surfaces and textures of the superstructure, under croft, piers, abutments and landscape.

The combination of treatments and design promotes the perception of the bridge being an elevated

street rather than a motorway flyover.

The Project will result in a number of transport benefits for the State highway network and the

local road network (including public transport and walking and cycling) as well as new buildings,

structures and landscape treatments for the Basin Reserve area.

Construction of these transportation improvements is currently scheduled to start in 2014/15.

2.3 Related Projects

The Project forms part of the Tunnel to Tunnel package of works that in combination would

improve traffic and transportation between the Terrace Tunnel and Mount Victoria Tunnel. The

Tunnel to Tunnel package also comprises:

• The Buckle Street Underpass as part of the National War Memorial Park project by the Ministry

of Culture and Heritage. This project is currently under construction and expected to be

completed by the end of 2014.

Other NZTA studies of SH1 sections that are also being considered or are being progressed

concurrently within Wellington:

• Duplication of Mount Victoria Tunnel (construction planned for 2017/18).

• Duplication of the Terrace Tunnel (subject to feasibility investigation in 2013/14).

• Roading improvements along Cobham Drive and Ruahine Streets (construction planned for

2017/18).

While there are linkages between these projects, each one is complex and entails significant use of

resource. As a consequence each is being progressed separately while maintaining the appropriate

design standards and specifications in order to achieve the NZTA’s strategic objectives for the

RoNS.



3 Geometric Design

The geometric design defines the alignment and the width of the new and altered sections of road.

This section defines the constraints and the standards that have governed its development.

3.1 Constraints Governing the Design

3.1.1 Horizontal Alignment

The primary focus from an urban design and geometric perspective has been the alignment of the

bridge. There are a number of key constraints which have influenced the proposed alignment.

These are labelled on Figure 1- 4 and described below.

1. Minimising the amount of land needed to be acquired (St Joseph’s Church and Regional Wines)

The design has attempted to minimise the land needed to be acquired and hence the potential

physical impact on these two properties.

2. Alignment with historic and existing street pattern

The road network around the Basin Reserve has historically been a square and only in recent times

has it become more aligned with the circular cricket ground we know today. The perpendicular

corridors of Kent/Cambridge and Ellice/Buckle also provide a corner to the overall city street

pattern or ‘grid’. The design has aimed to adhere where practical to this street pattern by ensuring

a straight and perpendicular crossing of Kent/Cambridge and aligning with Ellice and Buckle

Streets.

3. Proximity to the Basin Reserve

Increasing the separation from the Basin Reserve is desired to reduce any visual, noise, or shade

effects on the Basin Reserve. The alignment of the bridge also aims to reinforce the outer ‘square’

surround of the reserve.

4. Effective use of Ellice Street frontage

To enable the most effective integration of the bridge with the city, the aim has been to extend the

straight alignment across Kent/Cambridge as far to the east as possible. This reinforces the

historic street edge, enabling the bridge itself to become a defining structure of the city block. This

alignment also makes it easier to achieve a positive outcome for the space under the bridge.

5. Former Home of Compassion Crèche

The Crèche relocation has been provided for in the NWM Park Project. Therefore the design of this

Project has focussed on ensuring an appropriate street relationship and frontage with the crèche in

its new location. Refer to Section 3.1.2 Vertical Alignment for further details.

6. Coordination with adjacent projects

The design has been coordinated with the current proposals for the NWM Park, the Mount Victoria

Tunnel Duplication, Public Transport Spine Study and Wellington City Council walking and cycling

Projects (Refer to Section 16).



Figure 1- 4: Horizontal alignment constraints

Key

1 Minimising land needed to be acquired (St Joseph’s Church and Regional Wines)

2 Alignment with historic and existing street pattern

3 Proximity to the Basin Reserve

4 Effective use of Ellice Street frontage

5 Former Home of Compassion Crèche

6 Coordination with adjacent Projects recognising competing demands.

3.1.2 Vertical Alignment

As drivers exit Mount Victoria Tunnel they currently descend into the valley before climbing up the

other side to Buckle Street. This involves a drop in elevation of 17m and then a rise back up of 15m

as illustrated in Figure 1- 5. The proposed alignment spans across the valley, into the Buckle Street

Underpass, reducing the change in height by approximately 8m (i.e. the drop in elevation is

reduced to approximately 9m and the rise reduced to approximately 7m).

6

1

4

2

3

1 5

6



Figure 1- 5: Existing Vertical Profile. Mount Victoria to Mount Cook through the Basin Reserve

There are a number of key constraints which have determined the vertical alignment. These are

labelled on Figure 1- 6 and described as follows.

1. Vertical Clearances – Passenger Transport Spine

The Project provides sufficient headroom under the structure for traffic, trolley buses and all

possible outcomes from the Wellington Public Transport Spine Study (by GWRC, NZTA and WCC).

2. Visual Impact – Pohutukawa Trees

The Project has aimed to ensure that the bridge is not higher than the existing Pohutukawa trees

that line the Basin Reserve.

3. Proposed Drainage

It is necessary to provide some longitudinal fall (minimum of 1%) on the bridge to enable water

that falls on the bridge to flow to collection devices. The Project proposes stormwater treatment

devices in two locations (within the park west of Cambridge Terrace and under the bridge south of

Ellice Street. The high point for the bridge has been set to deliver stormwater naturally to these

locations.

4. Buckle Street Underpass (NWM Park)

To integrate with the Buckle Street Underpass the vertical alignment needs to drop from the bridge

down in to the underpass.

5. Former Home of Compassion Crèche

In the zone between the bridge and the Buckle Street Underpass, the key consideration has been

maintaining a street frontage for the crèche, in its new location, that is as level as possible with the

footpath adjacent to the road and building without barriers or retaining structures being required.



Figure 1- 6: Vertical Alignment Constraints

Key

1 Vertical Clearances – Passenger Transport Spine

2 Visual Impact – Pohutukawa Trees

3 Proposed Drainage

4 Buckle Street Underpass

5 Former Home of Compassion Crèche

3.2 Design Speed

The proposed design speed is critical in defining the extent to which the desired outcomes can be

achieved. The lower the design speed the tighter the geometry and therefore the easier it is to align

with the existing street structure and accommodate other constraints.

The decision has been made that the new westbound SH1 will be a 60km/h design speed and a

50km/h posted speed. All other sections of road will have a design speed of 50km/h apart from the

Ellice Street link which will be designed for a speed limit of 30km/h. The following sections

describe the factors leading to this decision further.

3.2.1 Westbound SH1 Alignment Design Speed – The Bridge

The design speed for the westbound SH1 alignment has been a primary discussion point during a

number of Road Safety Audits. The desire is to keep the design speed as low as possible to:

1

2

3

3

4

5



• Maximise the separation between the bridge and the edge of the Basin Reserve;

• Provide the best possible urban design outcome; and

• Provide an appropriate transition on to the city road network. The majority of users

(approximately 60%) emerging from the Mount Victoria tunnel turn off the state highway

before the Terrace Tunnel. In this way, the State Highway acts as an urban arterial with drivers

generally wanting to get on and off to access the local street network rather than being a

through route only.

From a road safety perspective the risks associated with a 50km/h design speed were deemed

unacceptable. The key risk was that 50km/h designed curves would be unforgiving for drivers

travelling over the speed limit coming down the hill from the Mount Victoria Tunnel and the

frequency and severity of crashes would be unacceptable. Therefore a 60km/h design speed and

50km/h posted speed has been agreed. This decision has been agreed through the Road Safety

Audit process and through discussions with the NZTA at both a regional and national level. The

60km/h design speed provides a safer environment for vehicles travelling slightly higher than

50km/h coming down the hill from the Mount Victoria Tunnel.

As agreed with the Road Safety Auditors and the NZTA the 60km/h design speed for the preferred

scheme is based on urban road environment design criteria.

Due to the separated nature of the bridge and its approach, measures are likely to be required to

reinforce the legal speed limit of 50 km/h on the approach to the bridge. These measures could

include VMS signs, both at the beginning of the 50 km/h speed restriction entering the Mount

Victoria tunnel (at the eastern end) and at the end of the tunnel/start of the bridge. This could be

supplemented by a speed camera located between the exit of the tunnel and the bridge. This

enforcement would be similar to the system used in the Ngauranga Gorge for southbound traffic,

where a speed camera is effectively used to control speeds.

As the design is developed, coordination with the proposal for the Mount Victoria Tunnel

duplication will be important to ensure a consistent environment and messaging for road users.

3.2.2 Eastbound SH1 Alignment Design Speed – Kent Terrace to Mount

Victoria Tunnel

The eastbound SH1 route is realigned to enable it to have necessary clearance under the bridge and

then connect to the Mount Victoria Tunnel. Speed along this route is controlled by the existing

corner at the south end of Kent Terrace. The Project only includes minor widening of the lanes on

this corner so speeds at this point will continue to be well below 50 km/h. The new alignment from

this point is therefore based on a design and posted speed of 50km/h.

3.3 Design Standards

During the Scheme Assessment phase it was agreed with the NZTA that the adoption of the

standard NZTA RoNS guidelines would be destructive or prohibitively expensive given the sensitive

urban environment in which the Projects sits. The RoNS guidelines are more applicable to a rural

100km/h expressway rather than an urban street.

The geometric design is based on the Austroads Guide to Road Design.



3.3.1 Design Standards – SH1 Routes

The key design parameters that are achieved by the current design are listed in Table 1- 1.

Table 1- 1: Geometric Design Parameters – SH1 Routes

State Highway Eastbound Westbound

Design Guides: Austroads Guide to Road Design

Parts 3 and 6A

Austroads Guide to Road Design Parts

3 and 6A

Design Speed: 50km/h 60km/h

Criteria Minimum Standards Achieved (in the current design):

Horizontal Curves:

Curve Radius: 55m

Maximum Superelevation: 5%

(Table 7.5, Austroads Guide to

Road Design Part 3)

Curve Radius: 75m

Maximum Superelevation: 5%

(Table 7.5, Austroads Guide to Road

Design Part 3)

Vertical Curves:

Minimum Sag Curve: 685m

Minimum Crest Curve: 1060m

Minimum Curve Length: 34m

(sag curve)

(Tables 8.6, 8.7 and Figure 8.7

Austroads Guide to Road Design

Part 3)

Minimum Sag Curve: 800m

Minimum Crest Curve: 1200m

Minimum Curve Length: 32.5m (sag

curve)

(Tables 8.6, 8.7 and Figure 8.7

Austroads Guide to Road Design Part

3)

Grade:

8.0% (upgrade) for a length of

25m


Road Design Part 3)

6.0% (downgrade) for a length of

110m


Design Part 3)

Sight Distance:

Minimum Sight Distance: 49 m


Road Design Part 3)

Minimum Sight Distance: 65 m


Design Part 3)

Road Width

3.5m traffic lanes (with additional

provision for vehicle tracking and

curve widening)

0.5m minimum shoulder, 1.0m

where achievable.

3.5m traffic lanes (with additional

provision for vehicle tracking and

curve widening)

0.5m minimum shoulder, 1.0m where

achievable.

Vertical Clearance,

at significant road

crossings

6.1m minimum

(Figure A2, the NZTA Bridge

Manual)

6.1m minimum

(Figure A2, the NZTA Bridge Manual)

Bridge Structure N/A

Minimum Standard Achieved:

2 x 3.5m traffic lanes

2 x shoulder, 0.6m



2 x 0.5m edge barrier

1 x 0.4m deck drain

Sightline and lane widening where

required (varies; 0m – 5.3m)

Total width: 9.6 – 14.9m

The reasons for the geometric decisions in the design are as follows:

• The bridge horizontal alignment has been designed to meet minimum curve radii for 60km/h

design speed with 65m sightlines. This has led to the provision of sightline splays and widened

lanes on the curves of the bridge.

• The bridge has a high point where it crosses the eastbound SH1 lanes and falls away from this

point at a slope of approximately 1% in both directions. This provides the required clearance

and enables water run-off to be collected at either abutment.

• The westbound SH1 vertical alignment into the underpass aims to extend the minimal 1% grade

on the bridge as far west as possible to provide a street frontage to the relocated crèche

building.

• The eastbound SH1 horizontal alignment has been designed to meet minimum curves for

50km/h.

• The eastbound SH1 horizontal sightlines are constrained by the placement of bridge piers. A

balance has been found to reduce the cost of increased span lengths by using absolute

minimum sightline values. This approach is supported by the low speed environment for

vehicles travelling from Kent Terrace to Ellice Street.

• The eastbound SH1 vertical alignment between Hania Street and Brougham Street aims to

reach the same level as the westbound alignment as far west as possible. This minimises the

need for retaining structures and therefore the extent of encroachment into the St Joseph’s

Church property. This alignment also aims to tie into Ellice Street and Hania Street at existing

levels. The alternative of changing the level of these existing streets would have had further

impact on property.

The proposed geometric design is illustrated in Volume 5: Plan set.

3.3.2 Design Standards – Ellice Street Link

In addition to the changes to the SH1 alignments discussed above, there is one new local road being

constructed as part of the Project which links Ellice Street to Dufferin Street. This link road is a low

speed (10-30km/h), low volume link and meets the design criteria set out in Table 1- 2.

Table 1- 2: Geometric Design Parameters – Ellice Street Link

Criteria Value

Design Speed: <30km/h

Horizontal Curves: Curve Radius: 15m

Grade: ~10% (short distance)

Sight Distance: No restrictions to sight distance.

Road Width (Urban) 3.0m traffic lane (widened for vehicle tracking (14m bus) where



necessary)

No shoulder

3.0m shared path (minimum)

Vertical Clearance

(above) 5.2m minimum.

The design criteria for intersection layouts and operational details are discussed in Section 6,

Transportation Design.

3.4 Road Design Cross Sections

The proposed road cross sections are illustrated in Volume 5: Plan Set.

3.4.1 Lane Widths

New sections of road will meet minimum standards of 3.5m lanes and 0.5m shoulders as per the

tables above. This applies to:

• Adelaide Road / Rugby Street Intersection.

• Sussex Street On-Ramp.

• Paterson Street Off-Ramp.

• State Highway 1.

The two exceptions to this are:

• The link road between Ellice Street and Dufferin Street (3m wide lane between kerbs). This

narrower width is compliant with the WCC standard for a local road service lane and is in

keeping with the low speed environment at this location.

• The changes to Pirie Street (3m wide shared right and left turning lane). This narrower width is

in keeping with existing road environment on Pirie Street where lane widths are lower than 3m

and provides a balance with reduced footpath widths.

Lane widths and shoulder widths will be decreased proportionally where the new State Highway

alignments ties back into the existing road outside St Joseph’s Church. At this point the Project ties

into substandard lane widths on Paterson Street (existing lane width is approximately 2.75m).

During the detailed design process the cross section width and sight line provision may be

considered further. Examples may include marking lanes at widths narrower than 3.5m and

reducing forward visibility provision to optimise pier placement or minimise the width of the

bridge structure. Any reductions in width will have to be signed off through a Safety Audit process.

3.4.2 Bus Lanes

The bus lanes around the Basin Reserve are proposed to be 3.5m wide, as indicated on the

drawings. Cyclists will not be excluded from the bus-lanes; however, the improved shared

pedestrian-cycle facilities are expected to be their preferred route.



3.4.3 Walking and Cycling Design Standards

The scope of walking and cycling facilities is discussed in more detail in Section 6.1. This section

considers only the geometric design standards.

Walkways and Cycleways will be designed to the relevant Austroads Traffic Management and Road

Design Guidelines (Austroads Guide to Road Design Part 6A: Pedestrian and Cyclist Paths) as well

as the Wellington City Council Code of Practice for Land Development, May 2011.

A 3 metre wide shared pedestrian and cyclist facility will be provided on the bridge to connect the

path from the Mount Victoria Tunnel through to the pedestrian/cycleway along Buckle Street.

Through stakeholder and public engagement (primarily in 2012) feedback has been received

regarding a desire for a wider facility on the bridge and if possible segregation between people

moving in opposing directions. This feedback has been considered by the Project team and based

on the expected usage and feedback from other successful Projects around the country the

proposed width is seen as appropriate. The proposed 3m width is consistent with the proposals for

an upgraded facility within the Mount Victoria Tunnel. The Austroads guidelines recommend a

minimum width for a commuter (user) path of 2.5m. As is the case on the bridge where there are

adjacent barriers then a suitable clearance should be provided (minimum of 0.3m). This has been

provided on the bridge (effective width is 3.4m, and on the dedicated walking/cycling ramp where

the width between barriers is 3.1m). Figure 1- 7 and Figure 1- 8 are extracts from Volume 5: Plan

Set.

3.4.4 Shoulders and Kerbs

Only minimum shoulders are provided on all new sections of road, typically 0.5m (including

channel). This does not meet recommended shoulder widths for highways, but is typical for urban

roads in Wellington. The Project proposes kerbs on all new sections of road including on the

bridge. Again this is common for the urban environment within Wellington.

The absolute minimum shoulder width recommended by the bridge manual (0.6m) will be

constant on both sides of the bridge. On the straight section of the bridge a kerb will be provided

with 0.4m separation from the barrier face on the southern edge (to collect stormwater). Where the

bridge widens around the curves a kerb will be provided on the inner side of each curve 0.6m from

the edge line, the distance from the kerb to the barrier face will vary between 0.4m and 4.5m

depending on the widening required for sightlines.



Figure 1- 7: Proposed Walking and Cycling Facility on Bridge

Figure 1- 8: Proposed Walking and Cycling Facility on Bridge Ramp

All of the kerbs will be mountable with a height of approximately 75mm above the road surface and

may be perforated to allow for the collection of stormwater. Kerbs will not be provided on the high

side of the bridge. The use of low or standard kerbs on bridges is not common in state highway

situations but is used widely in lower speed environments. The precise detail of this aspect will be

provided later in the design.

Some of the positives of using kerbs are listed below:

• Potential road safety concerns.

• Consistent appearance with adjacent sections of road.

• Provides opportunity to collect stormwater close to the box girder of the structure negating the

need for potentially visible drainage systems.

• Reduces the risk of vehicles cutting corners where widening for sight lines is provided.

The key disadvantage is potential road safety concerns.



3.4.5 Traffic Barriers

Consideration has been given to different Test Level (TL) barriers as defined by the bridge manual.

The proposed road safety barrier on the bridge is a “Texas HT” TL-5, 0.82m high concrete barrier

with a steel rail to a total height of 1.1m. On the approach to and exit from the bridge the road

safety barrier will be a TL-4, 0.82m high concrete barrier. The eastern ends of the barrier will be

protected by TL-3 crash cushions.

As part of the detailed design it may be appropriate to further consider whether a TL-4 barrier

would be sufficient for the bridge and whether alternative barrier systems that reduce the visual

depth of the bridge may be appropriate. If an alternative solution is proposed then any effects on

the noise outcome will also need to be considered. The current barrier level was determined by the

NZTA’s National Safety Manager so any reduction in level of protection would have to be

adequately justified.



4 Signs and Markings

4.1 Traffic Signs and Pavement Markings

The drawings illustrate the preliminary layout for information/directional signage. The relevant

drawings are included in Volume 5: Plan Set.

All traffic signs and pavement markings shall comply with the Manual of Traffic Signs and

Markings (MOTSAM) and its replacement, the Traffic Control Devices (TCD) Manual and

Specifications (expected to be available at the date of construction). Destination signs and

suggested wording are to be agreed between the NZTA and Wellington City Council.

Material and construction specifications shall be in accordance with the NZTA publication

‘Standards for the Manufacture and Maintenance of Traffic Sign Posts and Fittings’ and the

reference standards contained within. All posts not protected by barriers shall be of a frangible

design and construction in accordance with a safe systems approach.

Signs shall be positioned to maintain clearances in accordance with MOTSAM and its replacement

the TCD Manual and Specifications.

Overhead mounted signs (e.g. gantries) shall use Class 1W Reflectorised sheeting as defined in

AS/NZS 1906, other signs must use Class 1 sheeting minimum. All traffic signs must have either

graffiti guard or dew guard sheeting as appropriate to their location.

The key new signs are described in more detail below:

• New VMS between Mount Victoria Tunnel portal and exit road from Wellington College

(mounted in the road shoulder and protected by a TL-4 concrete barrier). This VMS can advise

of a closure on the bridge or further downstream to enable motorists to take alternative routes.

• ADS-01 new sign advising of exit for traffic travelling down Cambridge Terrace (City Centre

and Oriental Bay).

• ADS-02 new sign advising of exit for traffic travelling down Cambridge Terrace (City Centre

and Oriental Bay) and confirmation for SH1/2 traffic (Porirua and Hutt Valley).

• ADS-03 new sign advising correct lane for traffic approaching Adelaide Road / Rugby Street

intersection (Left - Newtown and Island Bay & Right - Porirua and Hutt Valley).

• ADS-04 new sign advising correct lane for traffic approaching Buckle Street from Sussex

Street.

• GEN-01 new sign advising school traffic to use the left lane approaching the Dufferin Street –

Paterson Street intersection.

• GAN-02 new gantry across Vivian Street advising traffic of correct lane to use (similar to the

existing gantry on Kent Terrace). Or alternatively two smaller signs either side of the road.

• New directional sign on the entrance to the tunnel to ensure the correct lane is used.

Other new smaller signs include (but are not limited to):

• Bus lane signage for all new bus lanes.

• Shared space signs for link roads between Buckle Street and Ellice Street and between Ellice

Street and Dufferin Street.



• Pedestrian / Cycle shared path signs on all new paths.

• Permanent warning signs for merges and diverges at various locations.

• Stop signs at entry to and end of link road between Ellice Street and Dufferin Street.

• Clearway signs for Vivian Street.

• Permanent warning curve advisory signs prior to bridge.

• Speed limit confirmation signs on approach to bridge – potentially Active Warning Signs

(AWS).

• Local road directional signs.

The sizes and positions of the signs have been developed following feedback from the Safety Audit

Review Team and the Visual Effects Specialist. The signs have in general been restricted to road

side signs instead of gantry or flag-type structures to minimise the impact of views along key

corridors. The one exception to this is on Vivian Street where a gantry is currently proposed. An

alternative option of two separate road side signs has been considered and should be investigated

further as part of detailed design. It should be noted that safety and legibility are considered

paramount when signage is considered.



5 Traffic Signals and Intelligent Traffic Systems

5.1 Traffic Signals Design

All traffic signals shall comply with:

• AUSTROADS Guide to Traffic Management” series – Part 6: Intersections, Interchanges and

Crossings Section 5, Part: 9 Traffic Operations Section 7.1 and Part 10: Traffic Control and

Communications Devices Section 8;

• Signals New Zealand User Group (SNUG) the National Traffic Signal Specification - Revision 3

- 1 January 2006, available from the IPENZ website;

• Land Transport Rule: Traffic Control Devices 2004, Section 6: Traffic Signals; and

• The Traffic Control Devices Manual (TCDM).

The signal design and SCATS settings will be developed by a suitably qualified signals engineer and

undergo an independent peer review by another recognised signals engineer at the commissioning

phase.

New or amended signals are proposed at the following locations:

• Vivian Street / Kent Terrace / Cambridge Terrace / Pirie Street;

• Cambridge Terrace and Kent Terrace pedestrian / cycle crossings and bus priority;

• Ellice Street (SH1) pedestrian / cycle crossings;

• Dufferin Street / Paterson Street intersection and pedestrian / cycle crossings;

• Rugby Street / Adelaide Road pedestrian / cycle crossings; and

• Buckle Street / Arthur Street / Taranaki Street intersection.

Consideration needs to be given to the design and operation of intersections and pedestrian/cycle

crossings in close proximity to the SH1 signals to minimise obstruction of vehicles entering or

exiting the signal intersections and being restricted access to SH1. Intersections must complement

the design (e.g. SCATS linkage maintained or enhanced to provide better signal co-ordination on

SH1 and other important subsystems).

Adjustments to signal timings and SCATS settings at each of the above intersections should be

implemented in order to optimise performance and changes in traffic demands on SH1 as a result

of increased capacity and the removal of existing constraints.

5.2 Intelligent Traffic Systems (ITS)

This section of SH1 is required to be managed using variable message signs, incident detection

systems and potentially variable mandatory speed limit signs. All these tools will need to be located

carefully to optimise performance.

5.2.1 Design Guidelines and Specifications

The NZTA have developed a series of specifications for the supply and installation of ITS

equipment on state highways. The supply and installation of ITS equipment shall comply with

these specifications (updated as at the date of construction). Specifications can be found on the

NZTAs website (http://www.nzta.govt.nz/resources/intelligent-transport-systems/).



5.2.2 Existing ITS Infrastructure

The following existing ITS infrastructure has been identified within the Project Area.

• Three wireless CCTV cameras (Adelaide Road (mast), Kent Terrace (gantry, including VMS)

and Dufferin Street (mast))

• Wired CCTV camera (Buckle Street/ Sussex Street)

• Wireless transmitter/ receiver (Buckle Street/ Cambridge Terrace)

• Wireless VMS on the corner of Rugby and Sussex Streets

5.2.3 Additional Information

The NZTA require the Project area to be future proofed for ATMS, which will include, but is not

limited to, the provision of twin ducts suitable for fibre optic and pull pits. Automatic Number

Plate Recognition (ANPR) may be used in this area in the future for enforcement

5.2.4 VMS Requirements

The NZTA require VMS to inform westbound state highway users of road closures west of the

Project Area (especially the Terrace Tunnel). The preferred location for the VMS is between the

Mount Victoria Tunnel and the bridge to allow Cambridge Terrace to be used as an alternative

route.

5.2.5 Scope of Work

The following list outlines the proposed scope of work of the Project:

• No change to CCTV camera and mast at Adelaide/Rugby intersection, Sussex/Buckle

intersection and the CCTV camera, VMS and gantry across Kent Terrace. Although some

changes may be made to the existing arrangement as part of the undergrounding of Buckle

Street.

• Raise the mast and CCTV camera at Dufferin/Patterson intersection to be at least 5m above

bridge carriageway (a 15m mast should suffice). The new camera should retain all current view

shafts.

• Provide new short mast near Ellice Street to monitor the Eastbound SH1 carriageway under

the bridge.

• Relocate wireless receiver/transmitter on Buckle Street (under proposed bridge) to a new

location to retain current coverage (potentially on bridge).

• Consider providing additional fixed cameras on any of the masts for the NZTA traffic webcams

(publicly accessible).

• Extend current fibre optic from Buckle Street to Brougham Street (inside bridge with

appropriate pull pits etc.) and connect to masts at Ellice & Dufferin Streets. Future proofing

should allow two 100mm ducts suitable for new fibre optic installation in the future.

• Retain the current NZTA traffic count sites following construction.



6 Transportation Design

This section discusses the development of the design for the different modes of transport that will

be affected.

6.1 Existing Pedestrian and Cyclist Facilities

The current off-road facilities for walking and cycling are shown in Error! Reference source

not found.. All existing facilities will be maintained or enhanced by the Project.

Figure 1- 9: Existing Walking and Cycling Facilities

6.2 Pedestrian and Cyclist Options Considered

A number of new facilities have been considered during the design process and this section

describes the process undertaken.

6.2.1 Pedestrian and cyclist facility on the Bridge

During the 2011 community engagement the NZTA asked for feedback on whether or not to include

a walking and cycling facility on the bridge. The feedback received suggested that this facility

would be seen as a significant positive outcome from the Project. This view was strongly supported

by two of the key stakeholders WCC and GWRC. An extract from the WCC submission reads;



“If a flyover option is constructed Council considers the cycleway/walkway to be an essential component … Council would not support either flyover option without inclusion of a provision for walking and cycling”.

These sentiments were echoed by GWRC and many of the community and stakeholder

submissions.

Figure 1- 10: Walking and cycling facility as presented through public engagement in 2011

Following this feedback the NZTA considered three different options being:

• Not providing a walking and cycling facility.

• Building a facility as part of the bridge structure.

• Providing structural capacity to enable a walking and cycling facility to be added in the future.

The third option was considered based on the expectation that there would be a significant increase in walking and cycling through the Mount Victoria Tunnel on completion of the tunnel duplication. Estimates were that initially it would be utilised by approximately 350 users (walkers or cyclists)



daily and that this figure may increase over time and after the tunnel duplication up to 1750 users per day.

Based on feedback received and an assessment of the transport benefits, health benefits and costs, the NZTA decided to provide a walking and cycling facility on the bridge. This facility is expected to deliver a number of positive outcomes, including:

• Completes a spine of quality walking/cycling facilities within Wellington City from Mount

Victoria to Willis Street;

• Provides safety benefits for pedestrian/cycling users travelling east-west who will not have to

cross two uncontrolled and two controlled crossings;

• Encourages walking and cycling by removing the need to drop and climb eight vertical metres

and undertake multiple road crossings;

• Provides a thinner edge to the structure reducing the need for other architectural edge

treatments and associated cost;

• Provides activity on the structure in the form of pedestrians and cyclists, informing drivers that

they are in an urban environment and not on a ‘motorway flyover’. Adds activity to the

structure when viewed from below;

• Avoids future retrofitting to the structure which could be costly and provide a less than

desirable architectural outcome.

6.2.1.1 Design of the Facility

The decision was made to place the pedestrian and cyclist shared facility on the northern edge of the structure instead of the southern edge for the following reasons:

• It was the preferred location proposed by advocacy groups;

• The existing Mount Victoria Tunnel facility is on the northern side as will be the new facility

within the new Mount Victoria Tunnel; and

• The access on to and off the pedestrian and cyclist shared facility on the northern edge is much

simpler than a southern alternative. For a pedestrian and cyclist shared facility on the southern

edge users would have to travel under the main bridge structure at both ends to connect with

the existing facilities adjacent to the Project. Travelling under the main bridge structure would

mean that users would have to ascend and descend multiple times on their journey which

would reduce its desirability.

The existing pedestrian and cyclist shared facility through the Mount Victoria Tunnel currently terminates at the corner of Paterson Street and Brougham Street. The new facility would continue this path around St Joseph’s Church (see Figure 1- 11)



Figure 1- 11: Model view from walking and cycling path with St Joseph’s Church on the right

Rather than rising at the same level as the bridge the walking and cycling facility does not start rising until the path has passed the main window of St Joseph’s Church. This design solution prevents there being a structure immediately in front of the Church window. The walking and cycling ramp then splits from the roadside footpath and rises to join the bridge at a gradient of 1 in 12, following a constant horizontal curve. The ramp is aligned to the edge of the eastbound SH1 lanes heading towards the Mount Victoria Tunnel. It is not possible for this route to cross over SH1 eastbound until it can achieve a clearance of 6.1m. This does not happen until north of Ellice Street. Once the westbound route crosses the eastbound lanes the pedestrian/cycle facility connects on to the bridge. This can be seen in Figure 1- 12.



Figure 1- 12: Plan view of pedestrian ramp to bridge

6.2.2 Ellice Street Link

6.2.2.1 Existing Situation

Currently pedestrians from Mount Victoria walking to Dufferin Street have to cross both the eastbound and westbound SH1 route (see Figure 1- 13). The Basin Bridge will lift the westbound SH1 traffic above ground level with pedestrians passing underneath the bridge.



Figure 1- 13: Existing Pedestrian Crossing of SH1 Eastbound and Westbound on Dufferin Street

Through the 2011 public engagement there was a significant amount of feedback on the importance of the connection from Ellice Street (Mount Victoria) along Dufferin Street to the schools south of Paterson Street (St Marks Church School and Wellington College). The following is an extract from the St Mark’s Church School submission;

“The Board’s foremost concern is the safety of our pupils, staff and parents. In that regard we need assurance from the NZTA that … the route from car to school is safe (e.g. with controlled crossings, over-bridges, adequately lit and monitored subways for cyclists and pedestrians”.

6.2.2.2 Options Considered

In response to the suggestions received the Project team has considered ways to provide grade separation between pedestrians/cyclists and eastbound State highway traffic, noting that the proposed westbound bridge would already provide separation from traffic moving in that direction.

A ramped pedestrian footbridge would involve significant lengths of ramps to achieve the necessary clearance over the traffic lanes. Therefore, the alternative of a subway was considered.

The eastbound state highway lanes climb from Kent Terrace to the Mount Victoria Tunnel. By using this grade and by slightly lowering the surrounding ground level in this area it is possible to provide clearance for pedestrian and cyclist access.

The Project team spent considerable time developing a wide, open, high quality underpass hoping it could address a number of the Crime Prevention through Environmental Design (CPTED) concerns that structures of this kind raise. It was hoped that an underpass could provide a grade



separated outcome addressing the perceived safety risks of mid-block signalised crossings on SH1 and providing travel time savings for vehicles by removing the crossing.

Figure 1- 14: Model image of possible underpass under SH1 Eastbound (Paterson Street), from Dufferin Street looking north towards Ellice Street

Although a range of solutions were considered it was not possible to provide a facility that had appropriate visibility to make it a safe and attractive route for users. The decision was therefore made to provide a direct at-grade crossing that would be controlled by traffic signals.

An at-grade crossing also enabled a vehicle lane to be included providing a connection from Ellice Street to Dufferin Street and Adelaide Road. The proposed pedestrian and cycling link is shown in Figure 1- 15.



Figure 1- 15: Link from Ellice Street to Dufferin Street

6.2.3 Pedestrian and cyclist shared path from Adelaide Road to Paterson

Street

During meetings with WCC officers in February 2012, they expressed a desire to have a shared path around the eastern edge of the Basin Reserve for situations when cyclists and pedestrians cannot use the path through the Basin Reserve.

The preferred scheme assumes that the existing footpath facilities could be used for this purpose and any improvements and signage would be provided by WCC. The preferred scheme does provide pedestrian and cyclist signalised crossing points at the Rugby Street / Adelaide Road intersection and the Dufferin Street / Paterson Street intersection. These pedestrian and cyclist signalised crossing points will also be provided across Kent Terrace and Cambridge Terrace north of the Basin Reserve.

By providing these crossing facilities, the scheme allows for any works that WCC may wish to undertake to connect to the facilities proposed by the NZTA as part of the scheme.

6.2.4 Shifting the signalised crossing on Kent / Cambridge Terraces closer

to the Basin Reserve

The Project shifts the signalised crossing on Kent / Cambridge Terraces as close as possible to the Basin Reserve and adds cyclist crossing facilities. This is shown in Figure 1- 16.



Figure 1- 16: Northern entrance to the Basin Reserve

The reason for shifting these crossing points further south is to better align with the desire lines along Buckle Street and Ellice Street and access to these routes from the Basin Reserve. The crossings cannot be shifted further south because:

• On Kent Terrace any shift further south would mean that the buses would not be able to travel

right up to the limit line for the signals due to the downstream curve. In turn this would mean

that the priority signal at this crossing point could not be used. Additionally, there were also

concerns about potential safety risks locating the signal crossing underneath the shadow of the

structure; and

• On Cambridge Terrace the same concerns about potential safety risks around signal crossing

underneath the structure also existed. Additionally the sightlines to the crossing point may

have been compromised if the crossing was shifted closer to the Basin Reserve.

6.2.5 Pedestrian entrance on the northern side of the Basin Reserve

The Project includes a change to the priority on the road linking Buckle Street with Ellice Street from vehicles to pedestrians and cyclists. The purpose of this change is two-fold:

• To enhance the pedestrian and cyclist connection between the Basin Reserve and Kent and

Cambridge Terraces; and

• To emphasise the pedestrian plaza leading into the Basin Reserve entrance.



The Project includes a raised shared space constructed across the link road (refer Figure 1- 16). The

space will be clearly signposted as shared space with priority given to pedestrians and cyclists. The

existing zebra crossing in this location will be removed and it will not be replaced by a formal

crossing.

6.2.6 Pedestrian entrance on the southern side of the Basin Reserve

The pedestrian facilities on the southern side of the Basin Reserve will be altered to provide shorter

crossing distances for pedestrians and cyclists. This is possible due to the reduction in traffic using

this part of the road network. The existing and proposed arrangement is show in Figure 1- 17.

Figure 1- 17: Southern entrance to the Basin Reserve

6.2.7 Summary of Proposed Facilities

The proposed walking and cycling links on completion of the Project are shown in Figure 1- 18.



Figure 1- 18: Proposed Walking and Cycling Facilities

A shared path for pedestrians and cyclists is located on the northern side of the bridge.

All existing at-grade links (including accessible links) for pedestrians and cyclists within the Project

Area are maintained. This includes the pedestrian and cyclist route through the Basin Reserve and

the footpaths around its perimeter. A shared use path will be provided instead of the existing

footpath from the pedestrian crossing on Kent Terrace and along the northern side of Ellice Street.

This path will cross SH1 eastbound (Paterson Street) at a signalised crossing and then connect to

the intersection of Dufferin Street and Paterson Street.

The landscaping of the area between Sussex Street and Cambridge Terrace will provide several new

links (including an accessible link that does not currently exist) between Tory Street and

Cambridge Terrace. These routes will be accessible by both pedestrians and cyclists.

The area to the north of the Basin Reserve will be made more open with removal of the existing

planted area in favour of a pedestrian plaza.

The pedestrian connection from Adelaide Road through to the southern Basin Reserve entrance

will be modified to reduce the number of traffic lanes that need to be crossed.

There have been various discussions around the potential for a controlled crossing at the northern

end of Sussex Street to allow safe and efficient access to the Basin Reserve at this location. A

crossing in this location raises some road safety and efficiency concerns and it was decided that the

demand in this location is not sufficient to warrant a controlled crossing.



6.3 Local Road Changes (including Bus Lanes)

This section describes the proposed modifications to the local road network. It should be noted

that currently the south side of the Basin Reserve is part of SH1 but following completion of the

Project it will become local road.

6.3.1 Southbound around Basin Reserve (Kent Terrace to Adelaide Road)

6.3.1.1 Kent Terrace to Dufferin Street

On the approach to the pedestrian signals on Kent Terrace the current bus lane will end. Buses

need to merge across two general vehicle lanes (with the assistance of a bus pre-signal) before

accessing the new bus lane that connects to the Dufferin and Paterson Street intersection (starting

on the corner of Kent Terrace and Dufferin Street). The bus lane stops approximately 30m from the

stop line of the Dufferin and Paterson Street intersection to make it clear that school traffic can use

this lane.

Extending the bus lane from this intersection back to the pedestrian signals on Kent Terrace was

considered, but provided minimal benefit since the buses need time to merge across to the third

lane anyway (the two kerbside lanes lead to the Mount Victoria Tunnel). Also there is limited space

to fit four lanes with appropriate lane widening around the Kent Terrace / Ellice Street corner.

Figure 1- 19: Kent Terrace to Dufferin Street



With the construction of the bridge, the traffic demands at the Dufferin and Patterson Street

intersection will be significantly reduced since any westbound traffic on SH1 which currently uses

the intersection and travels around the Basin Reserve will use the bridge instead. The Paterson

Street approach to the intersection widens to two lanes to provide adequate stacking distance so

that traffic does not queue up Paterson Street and block access to the bridge.

The signals will operate on a two phase cycle with the first phase being for traffic on the Paterson

Street approach and pedestrians/cyclists crossing Dufferin Street. The second phase will be for

vehicles and buses on Dufferin Street and pedestrians/cyclists crossing Paterson Street.

Access to and from Ellice Street and Hania Street will be maintained. Traffic leaving Mount

Victoria will be able to access the Mount Victoria Tunnel and Dufferin Street (via a low speed lane).

This lane has been designed to accommodate school bus traffic travelling from Wellington East

Girls College to St Marks / Wellington College. Zebra crossings will be located on Ellice Street.

6.3.1.2 Dufferin Street to Rugby Street

Providing a full bus lane on the section between Paterson Street and Rugby Street was included as

part of earlier designs. Further detailed analysis has shown that providing full bus priority facilities

would have limited effectiveness and would limit the space available for school drop-off facilities

and landscaping. With the reduced traffic flows circulating the Basin Reserve buses should be able

to travel this section of Dufferin Street with minimal delay.

At the corner of Dufferin Street and Rugby Street a bus lane begins. This bus lane extends through

the Adelaide Road and Rugby Street intersection.

The current southbound bus stop on Adelaide Road will be relocated to Rugby Street just before

the intersection. This change is driven by a desire to move the existing unsafe bus stop (which is

currently located around a sharp blind corner) closer to the schools area. To facilitate this change

the footpath will be widened to provide a waiting area.



Figure 1- 20: Dufferin Street to Rugby Street

The intersection of Adelaide Road and Rugby Street is designed to operate as a free flow

intersection with pedestrian/cycle signals forming the only phasing control. In the first phase all

vehicle movements are permitted while the other accommodates all pedestrian / cycle movements

on demand.

6.3.2 Northbound around Basin Reserve (Adelaide Road to Cambridge

Terrace)

6.3.2.1 Rugby – Sussex Streets

The planned WCC bus lane on Adelaide Road will terminate at the current bus stop adjacent to

McDonalds. Stopping the bus lane early will increase the stop line capacity for northbound vehicles

on Adelaide Road. Northbound buses will travel through the intersection in the general vehicle

lane. An option with the northbound bus lane continuing through the Adelaide Road and Rugby

Street intersection was considered but it has a significant impact on the efficiency of the

intersection and little if any benefit for buses.



Figure 1- 21: Rugby Street to Sussex Street

In the event of an unexpected closure of the Bridge or Buckle Street Underpass, traffic will be

diverted around the Basin Reserve. To accommodate this potential increase in demand on Rugby

Street these traffic signals could be programmed with a continuous vehicle phase (limiting access

for pedestrians). This phase could be activated by the NZTA or WCC traffic control centres if

necessary.

From a link capacity perspective three lanes are not required northbound around the Basin Reserve

(on Sussex Street). A desirable outcome would be to reduce the road space and enhance active-

mode use in this location.

However, there is insufficient space between the Rugby Street / Adelaide Road intersection and the

curve at the corner of Rugby Street and Sussex Street to merge from three lanes to two or safely

start a bus lane. Once around this curve there is space to start a bus lane, but not enough room to

safely merge from three-lanes to two before the link would be required to diverge back to a total of

three lanes.

Therefore the Project will retain Sussex Street in its existing configuration. A bus lane will start

immediately after the northern end of Sussex Street as shown on the plans. The left lane will

connect into the Buckle Street Underpass, the centre lane will cater for buses turning right down to

Cambridge Terrace and the right lane will connect general traffic to Cambridge Terrace.



6.3.3 Adelaide Road, and Kent Terrace and Cambridge Terrace

There are no significant changes to Adelaide Road, Kent Terrace or Cambridge Terrace planned as

part of this Project. However, it has been assumed that the bus lanes on these roads operate in both

directions during both the AM and PM peak periods (as advised by WCC).

Buckle Street, immediately in front of the northern entrance of the Basin Reserve will remain. To

improve the amenity of the area for pedestrians a shared space environment will be created with

pedestrians and cyclists given priority over motor vehicles. Access to Ellice Street from this portion

of Buckle Street will be controlled by Give Way (as existing). A signal coordinated with the crossing

on Kent Terrace was considered but the potential queues would affect the quality of the shared

space and potentially queue back onto Sussex Street creating a safety risk.

Currently there are pedestrian activated traffic signals located on Cambridge Terrace and Kent

Terrace to the north of the Basin Reserve. They operate on demand and the pedestrian phase only

occurs when a pedestrian uses the push button. As part of the pedestrian phase there is a bus pre-

signal which gives priority to buses before general vehicles get a green light. The operation of these

signals will remain unchanged with the construction of the Basin Bridge. However, the signals are

shifted south to more closely match pedestrian desire lines. A separate cyclist crossing will be

added to the crossing to connect the shared pedestrian and cycle facility created as part of the

Project on Ellice Street to Buckle Street.

6.3.4 Vivian Street

Amendments are proposed as part of the Project to the Vivian/Kent/Pirie intersection to improve

access out of Mount Victoria without compromising the performance of SH1 and for other local

traffic. The proposed improvements are shown in Figure 1- 22 below and include; two approach

lanes being provided for traffic turning out of Pirie Street and three right turning lanes provided

out of Vivian Street.

Figure 1- 22: Vivian Street / Pirie Street Intersection

These changes require adjustments to be made to the median island south of Vivian Street and also

modifications to the footpath at the end of Pirie Street where it joins Kent Terrace.



6.3.5 Taranaki Street

Three SH1 lanes must be carried through the intersection to prevent significant congestion and

merging within the tunnel.

The Taranaki Street / Buckle Street intersection will be widened to allow three through lanes

westbound with a merge back to two lanes before Cuba Street. The two right hand lanes have been

chosen to merge based on the volume of users predicted on completion of the bridge.

In addition a left turn slip lane will be provided from Taranaki Street south to Buckle Street.

These modifications are shown in Figure 1- 23

Figure 1- 23: Taranaki Street Intersection

6.4 Parking Design

The Project has a number of effects on parking throughout the Project area. These are discussed in

detail in the Assessment of Traffic and Transportation Effects.

• All new on-street parking will comply with WCC standards. Off-street parking will generally

comply with the WCC standards (Appendix 2 of the Suburban Centre Rules, District Plan).



6.5 Schools Drop-off Area

The existing school bus drop-off area for St Marks School and Wellington College will be modified

as part of the Project to provide space for planting to mitigate visual effects of the Bridge from the

gates to the Government House grounds.



7 Geotechnical Engineering

7.1 Introduction

This chapter summarises the geotechnical considerations relevant to the Project. This material is

drawn from documentary sources along with further geotechnical investigations as summarised

below.

Note that this section does not specifically address the geotechnical issues associated with the

construction of the Northern Gateway Building. It is proposed that the Building sits on piled

foundations which are similar albeit smaller than the piles proposed for the Bridge. Further details

on the geotechnical considerations taken into account in the design of the Northern Gateway

Building are set out at section 10.3 of this report.

A preliminary geotechnical appraisal was carried out (Opus, 2010), and recommended a staged

programme of geotechnical investigations.

A two stage programme of geotechnical investigations was carried out. Stage one comprised

identifying, flushing and rehabilitation of the piezometers from the 1990s investigations for the

Tunnel-Link Scheme and monitoring since July 2010. Stage two was carried out from November

2011 to January 2012 and comprised a seismic refraction survey, drilling of five boreholes, six cone

penetration tests, excavation of six trial pits, installation of five standpipe piezometers and five

vibrating wire piezometers, and groundwater monitoring. The site work was followed by laboratory

tests.

Further to the investigations described above, the Alliance which will construct the Project,

undertook additional investigations during 2012 and 2013 including in the area of the Northern

Gateway Building.

7.2 Geology

7.2.1 Regional Geology

The regional geology of the area is shown on the 1:50,000 scale Geological Map 22 Geology of the

Wellington Area (Institute of Geological & Nuclear Sciences, 1996), as reclamation fill, marine

sediments and alluvial deposits underlain by Wellington Greywacke, see Figure 1- 24.

The main geological units in the area based on the geology map, other descriptions of the geology

and our site observations, comprise:

• Reclamation landfill (fr)

• Late Quaternary Holocene age, alluvium (fa) marginal marine sediments (fm).

• Pleistocene age alluvium (In).

• Late Triassic age Wellington Belt Greywacke, which generally comprises interbedded

sandstone, siltstone and mudstone.



Figure 1- 24: Regional Geology (after Institute of Geological & Nuclear Sciences, 2000)

7.2.2 Geomorphology

The Basin Reserve is bound by Mt Cook to the west, and the much higher Mt Victoria to the east.

Newtown valley is located along Adelaide Road to the south and the Te Aro flats to the north. SH 1

climbs down from Buckle Street in the Mt Cook area to the Basin Reserve grounds, and then climbs

up to the western portal of Mt Victoria Tunnel at the foothills of Mt Victoria hills. This route slopes

from a maximum of 27 m above mean sea level near Taranaki Street, and drops sharply to a

minimum of 5 m above mean sea level in the Basin Reserve area before rising again to 23 m above

mean sea level at the Mt Victoria tunnel portal.

Given that the Basin Reserve area was a low lying swamp prior to the 1850s; the then colonial

government planned an inland dock at the present Basin Reserve, with a canal leading from the

Wellington Harbour between Kent Terrace and Cambridge Terrace. However, this plan did not

reach fruition as the area was uplifted in the 1855 Wairarapa Earthquake, and the inland dock

proposal was abandoned.

At present there are no open streams or water courses in the area. Historical maps by Bastings

(1936) and The New Zealand Company (c.1840) indicate that there were a number of small streams

crossing the area of the current State Highway, see Figure 1- 25. The figure shows that some of

these streams have been culverted as the city developed, and now run under Paterson Street, Ellice

Street and Cambridge, Kent Terraces.

Basin

Reserve



Figure 1- 25: Historical waterways as presented in previous Groundwater Study – Stage 3 Report for Tunnel-Link Project (Opus, 1992)

7.3 Site Investigations

7.3.1 Previous Site Investigations

Previous known site investigations in the area comprised:

• Wellington Urban Motorway, Taranaki Street to Tory Street Section, Drilling Supervision &

Laboratory Testing (Brickell Moss Rankine & Hill, 1972). Site investigations comprise five

boreholes identified as “B” series bore holes in Tunnel Link Study are used in developing the

geological section, Figure 3A & 3B.

• Wellington Urban Motorway Extension, Terrace Tunnel to Mt Victoria, Additional Site

Investigations 1989, Part 1 Factual Report (Works Central Laboratories, 1990). Site

investigations comprise 11 boreholes identified as “D” series in Tunnel Link and 68 static cone

penetration tests identified as “C” series in Tunnel Link Study are used in developing the

geological section, Figures 3A & 3B.

• Tunnel – Link, Wellington Urban Motorway Extension, Terrace Tunnel to Mt Victoria Tunnel,

Preliminary Geotechnical Appraisal (Works Consultancy Services, 1991a).

• Tunnel – Link, Wellington Urban Motorway Extension, Terrace Tunnel to Mt Victoria Tunnel,

Groundwater Study – Stage 2 (Works Consultancy Services, 1991b).

The locations of the previous site investigations are shown on Figure 1- 27 and were used in

developing the geological section shown in Figure 1- 26 at the end of this section.



7.3.2 Site Investigations for the Basin Bridge Project

Site investigations comprising boreholes, static cone penetration tests, trial pits, machine auger

holes, seismic refraction survey and laboratory tests were carried out by Opus between November

2011 to January 2012, and then by the Memorial Park Alliance between November 2012 and March

2013. The investigations comprised:

• Drilling of fifteen boreholes to depths of between 19.5 m and 45 m. Standard Penetration Tests

(SPT) were carried out at depths of 1 m intervals during drilling.

• Recovery of soil samples for laboratory testing

• Pump well installation and testing

• Installation of standpipe piezometers and vibrating wire piezometers in selected boreholes at

different horizons to monitor the water table variations

• Six trial pits to depths of between 4.0 m and 5.0 m

• 27 Static Cone Penetration Tests

• Two Machine Auger Holes to shallow depths of 5 m to 6 m

• Seismic Refraction Survey to determine the rock profile

The locations of the site investigations are shown on Figure 1- 27 at the end of the report.

7.4 Ground Conditions

7.4.1 Stratigraphy

We have divided the sub surface ground profile into 4 units for this assessment on the basis of the

regional geology and the results of past and recent site investigations. These units are summarised

in Table 7-1 and shown on the geological long section presented in Figure 1-26.

Bedrock was not encountered in BH 603 and the borehole was terminated at 40 m depth. This may

be related to the presence of an inactive fault.

Table 7-1: Generalised Ground Conditions

Unit Depths Typical SPT N Description

1 1.5 m to 3.5

m Less than 10

EXISTING FILL

The fill encountered generally consists of silty and

sandy gravels.

2

Typically 3-

7m depth. Up

to a depth of

9 m

Typically 10 to 30,

some over 50,

some less than 10

RECENT ALLUVIUM

Interbedded loose to medium dense sandy gravel,

gravely sands, silty sand, and firm to stiff silt, clay and

gravelly sandy silt and organic silts

3

9 m to up to

maximum 40

m penetrated

Typically 15 to 30,

becoming 30 to

50 towards base

of unit

OLDER ALLUVIUM

Interbedded medium dense, dense and very dense

sands, gravels and silts with some organic silt. The

gravels encountered in the boreholes were typically

fine to coarse sized, sub-rounded to sub-angular,



moderately and highly weathered.

4 11-40m

penetrated Typically 50+

WELLINGTON GREYWACKE

Highly weathered to completely weathered

sandstone, siltstone and mudstone. Extremely weak

to Moderately strong at depths greater than 35m.

Moderately strong contains crushed and shattered

zones

7.4.2 Groundwater

A full description of ground water conditions is provided in TR20, and is briefly summarised here.

The Basin Reserve area comprises a complex groundwater regime, including sub-artesian and

artesian groundwater levels. The groundwater regime is controlled by the layered alluvial sequence

that has infilled the Basin Valley. This regime can be broadly characterised into three aquifers –

shallow, middle and deep aquifers. The artesian pressures are likely to be transmitted through

layers of higher permeability soils, separated by low permeability layers of silt clay and silt. These

layers are not necessarily continuous and the aquifers are likely to be leaky.

The shallow aquifer is in the Holocene age deposits and Upper Pleistocene age deposits, which

extend from ground surface down to depths of 12 m. This is an unconfined aquifer, and the

groundwater level is typically at ground surface. The ground conditions in the aquifer are generally

characterised by loose to medium dense sand, silt and gravels, with soft silty clay layers.

The middle aquifer is generally between depths of between 15 and 25 m (RL -9.5 m and RL -19.5 m)

below ground surface. This is a confined aquifer separated from the shallow and deep aquifers by

low permeability clay / silt layers, which may not be continuous. The ground conditions in this

aquifer are typically medium dense to dense silt, sand and gravel, with stiff clay / silt layers of

Pleistocene age. The groundwater level in this aquifer is artesian, with a groundwater head of

between 6 and 9 m above ground level (RL 11.5 m to RL 14.5 m).

The deep aquifer is located in the ground immediately overlying bedrock and the upper part of the

weathered bedrock sequence. The ground is characterised by dense gravels, sand and silt, and

weathered greywacke bedrock. The groundwater head in the deep aquifer is typically about 3 to 6

m above ground surface (RL 8.5 m to RL 11.5 m).

There will potentially be ground subsidence as a result of interference with groundwater during

construction. However, due to the short duration of the piling and providing that the piles are

designed and constructed appropriately there should be no effect.

7.5 Seismicity

7.5.1 Active Faults

The Project site is located in the Wellington Region, an area of high seismicity in New Zealand. The

region has number of major active faults and a subduction zone capable of producing large

earthquakes of Richter Magnitude 7.5 to 8.0, see Table 7-2. The Wellington Fault which is located



approximately 2.5 km away from the Project area is capable of producing magnitude 7.6

earthquakes with an average return period of 800 years.

Table 7-2: Active Faults in Region

Active Fault Recurrence Interval

of Rupture

Characteristic

Magnitude

Distance from Project

Area

Ohariu Fault 2,200 years 7.5 ~ 7.0 km

Pukerua Fault 3,500 years 7.4 ~ 10.0 km

Wellington Fault 610 – 1,100 years 7.6 ~ 2.5 km

Wairarapa Fault 1,200 years 8.0 – 8.3 ~ 16 km

(Source: Heron et al. (1998); IGNS (2000), Litchfield et al. (2004, 2006, 2010); Little et al. (2009,

2010); Schermer et al. (2004); Stirling et al. (2002); Van Dissen & Berryman (1996)

In addition, the subduction zone in the Cook Strait is capable of producing Richter Magnitude 8

earthquakes.

7.5.2 Ground Shaking

The active faults listed in Table 7-8, other Wellington Region faults and the tectonic subduction

zone in the Cook Strait area could give rise to significant levels of earthquake ground shaking in the

region. There is potential for significant ground shaking in the area during large earthquakes. The

Bridge Manual (Transit New Zealand, 2003) specifies the following return period factors (Ru),

appropriate to the importance level:

• 1.8 for bridges on the primary lifeline routes;

• 1.5 for independent walls supporting state highways, but not associated with bridges; and

• 1.3 for walls along local roads.

The site class is assessed as Class D. The depth to bedrock varies in the boreholes from 17 m to 40+

m.

For bridge abutments walls and retaining walls, this gives peak ground accelerations of:

• Abutment walls 0.96g

• Other retaining walls supporting State Highway 0.80g

• Retaining walls along local roads 0.69g

The above peak ground accelerations have been used for the preliminary design of the retaining

systems and liquefaction assessment.

7.5.3 Earthquake Induced Slope Stability Hazards

An earthquake induced slope failure hazard study (Works Consultancy Services, 1994) carried out

for and published by Greater Wellington Regional Council (1995) indicates a high slope failure

susceptibility of the slopes at the Mount Victoria Tunnel portal areas. The high slope failure

susceptibility could lead to very severe slope failure potential in a Richter Magnitude 7.5

earthquake associated with a characteristic rupture of the Wellington Fault, particularly at the west

portal of the Mount Victoria Tunnel.



The west portal of Mount Victoria Tunnel approach is 200 m away from the near end of the

abutment and therefore would be unlikely to affect these Project works. The site for this Project is

generally flat and not identified as susceptible to slope failure.

7.6 Liquefaction Hazard

7.6.1 Liquefaction Hazards

Liquefaction as a consequence of earthquakes could lead to foundation failure, subsidence and

lateral spreading, which could affect any surface development.

The Liquefaction Hazard study (Brabhaharan, 1994) of the Wellington Region carried out for the

Wellington Regional Council (1993) indicated Moderate Liquefaction Ground Damage Potential

with subsidence likely to be of the order of 100 and 250 mm.

7.6.2 Liquefaction Assessment

The loose to medium dense alluvial soils at this site are susceptible to liquefaction. An assessment

of the potential for liquefaction to be triggered in a design earthquake was carried out for the site

using the program LiquefyPro with the recent and past site investigations results. Elevated pore

pressures in artesian conditions have been considered in the analysis. Based on these calculations,

we expect thin loose lenses of silty sand that make up to 25% of soil within the top 9 m of the

ground profile and that the sands between 18.0 m to 23.0 m may liquefy in an earthquake having a

magnitude weighted peak ground acceleration of 0.96g. Each liquefiable lense within the top 9 m is

typically less than 1 m thick. The portion of soils that are potentially liquefiable within the top 9 m

of the soil profile varies considerably from location to location at this site.

Liquefaction subsidence of level ground is predicted to be in the order 200 to 250 mm. The total

subsidence of 30 mm to 100 mm is expected to result from liquefaction of layers in the top 9.0 m of

the ground profile. The remainder of the subsidence is expected to occur as a result of liquefaction

of the soils between 18.0 and 23.0 m deep. The LiquefyPro results are tabulated in Table 7-3 and

Table 7-4.

Table 7-3: Predicted subsidence at different locations as per 2011 site investigations

Event

BH 601

LiquefyPro

Predicted

settlement

BH 602

LiquefyPro

Predicted

settlement

BH 603

LiquefyPro

Predicted

settlement

BH 604

LiquefyPro

Predicted

settlement

BH 605

LiquefyPro

Predicted

settlement

Design

Event

0.96g, M8.1

112 mm 115 mm 77 mm 128 mm 45 mm



Table 7-4: Predicted subsidence at different locations as per previous site investigations

Event

BH D1

LiquefyPro

Predicted

settlement

BH D2

LiquefyPro

Predicted

settlement

BH D3

LiquefyPro

Predicted

settlement

BH D4

LiquefyPro

Predicted

settlement

BH D11

LiquefyPro

Predicted

settlement

Design

Event

0.96g,M8.1

61 mm 233 mm 76 mm 37 mm 111 mm

7.7 Summary of key geotechnical issues

The key geotechnical issues relating to the design and construction of a bridge at this site include:

• Stability and seismic performance of the approach embankments.

• Stability and seismic performance of retaining walls that support the approach fill. Lateral

displacement of the approach embankments can cause distress to the bridge.

• Static settlement of the approach embankments. The magnitude of settlement will affect the

type of walls that can be constructed. The time it takes for settlement to occur can affect the

construction programme and the cost.

• Liquefaction effects on slopes and pile foundations. Effects on piles include down drag causing

settlement of the pile, reduction in lateral stiffness and potential for increased ground

deformation of embankments, slopes and level ground.

• The high ground water levels and the presence of artesian water pressures. High groundwater

pressures will need to be managed during pile installation, particularly for bored piles.

• The variable ground conditions at this site.

• Space, noise and vibration constraints for the construction of piles within the urban

environment.

The embankments, slopes and foundations will be designed with this knowledge to ensure their

resilience.

Some of the key issues are discussed in more detail below.

7.7.1 Groundwater

Refer to section 7.4.2.

7.7.2 Ground Subsidence

It is unlikely that groundwater drawdown and consequent ground subsidence would occur with

groundwater management associated with the piles during construction as discussed below.

Based on the ground conditions, and assuming a 5 m reduction in the groundwater pressures in the

middle aquifer, subsidence of the ground assuming long term groundwater drawdown is assessed

to be of the order of 25 mm at the Grandstand apartments, and less than 10 mm at the Basin

Reserve Grandstand, Mitsubishi Motors, the Church and the shops along Ellis Street. Such



subsidence is not expected to cause an angular distortion exceeding 1/400 sufficient to cause

damage. This assumes long term groundwater drawdown.

Short term groundwater drawdown that is required for construction of the Project is likely to give a

much smaller subsidence. These assessments are consistent with the minimum subsidence of the

ground and associated settlement of the ground observed adjacent to the trench structure at

Wellington Inner City Bypass, where the groundwater was drawn down several metres for 12- 18

months during construction. In that case, the ground was similar Holocene and Pleistocene

deposits as that present in the middle and deep aquifer in the Basin Reserve area.

Nevertheless it would be prudent to monitor settlements and groundwater pressures in the area,

and carry out pre-construction structural surveys of key buildings. This would be appropriate to

ally the perception of possible effects to the buildings due to construction activating, piling,

vibration etc, and to provide a baseline for any claims by building owners. Groundwater monitoring

in the investigation boreholes holes is ongoing and will provide more than 12 months of baseline

readings prior to construction.

7.8 Scope of geotechnical works required

There are a number of geotechnical works that are likely to be required as part of the Project

including:

• Geotechnical investigations for detailed design purposes;

• Retaining walls and reinforced earth wall abutments;

• Ground improvements;

• Earthworks, including removal of potentially contaminated land;

• Pile construction; and

• Road pavement construction.

The following sections describe the proposed works and possible methods of construction.

7.8.1 Bridge piles

The proposed piles for the bridge are 900 mm to 1200 mm diameter bored piles founded at depths

of 30 m to 36 m in Greywacke, or, where the depth to Greywacke is greater than 35 m founded in

the dense to very dense alluvium.

Unlike driven piles, bored piles have the ability to be advanced through dense gravels and the

shear, crush and fault zones in the bedrock to a suitable depth to resist vertical and lateral loads.

Vibration and noise from bored pile construction should also be less than that generated from

driving piles. Also, large diameter piles are stiffer and more able to resist deformation compared to

driven piles.

Based on the results of the investigations and previous experience with piled foundations in these

units, we recommend a geotechnical ultimate end bearing capacity for single bored piles at least 30

m deep and embedded at least 5 pile diameters into the Greywacke or dense to very dense alluvium

of 4 MPa for scheme design. Geotechnical ultimate pile skin friction capacity of 200 kPa can be

used to calculate skin friction capacity for the portion of piles below a depth of the lowest

liquefiable layer, below a depth of 23m. These geotechnical ultimate capacities have to be factored

by 0.5 for static load combinations and factored by 0.7 for seismic load combinations.



Subsidence from liquefaction will cause soil above liquefied layers to drag on the piles and may

cause settlement of the pile head. It is recommended that piles are designed to have sufficient

capacity below a depth of 23 m to support the combined bridge dead load and liquefaction down

drag force for the earthquake case using a strength reduction factor of 0.5. The drag down forces on

a single pile from soil layers above a depth of 23 m (the base of the lowest liquefiable layer) can be

calculated assuming a skin friction of 60 kPa.

The piles will need to be embedded into non - liquefiable layers and be designed to provide

sufficient lateral resistance. Large diameter bored piles will have sufficient structural moment and

shear capacity to resist the lateral loads and limit displacement.

Piles can experience damage at the interface between liquefiable and non-liquefiable ground.. This

can be addressed through suitable pile design and construction.

There are a number of possible solutions to manage groundwater during construction. The exact

method of construction will be confirmed through detailed design. Particular measures that could

be considered are:

• Use of telescopic casing for construction of the piles. A larger diameter casing could be installed

down to the aquiclude between the shallow and middle aquifers. Then a smaller diameter

casing could be installed below this depth to the required founding depth. A further reduction

of pile diameter could be considered at the interface between the middle and deep aquifers.

• Use of small temporary depressurising boreholes drilled immediately in advance of drilling the

main pile. This will allow the groundwater response to be controlled and monitored. The main

pile can then also be excavated under static or balance water conditions.

• A contingency measure if leakage occurs would be to over drill and or grout the interface

between the pile or casing and the upper ground surface down to the base of the shallow

aquiclude..

Work undertaken to date suggests that any effects are likely to be minor and the recommendation

is to monitor during construction.

Bridge abutments piles through reinforced soil abutment blocks should be sleeved to allow for

displacement of the reinforced soil wall or approach fill in earthquakes without imposing large

lateral displacements/loads on the piles. Piles would be designed for negative skin friction effects

due to construction settlement and earthquake subsidence.



7.8.2 Abutments / embankments

Geometric Constraints

The space for side slopes for the approach embankments is constrained, particularly near the

bridge abutments where embankments of up to 5.5 m high are proposed. Therefore a portion of the

embankment sides, including the end of the approach embankments at the bridge abutments, will

need to be retained or reinforced.

Fill Materials

There is little cut compared to the quantity of fill needed to construct the approach embankments

and the material that is won from cuts is unlikely to be suitable for fill. Therefore we consider that

the majority of the embankment fill will be sourced off site, and probably from the Kiwi Point

Quarry, Newlands. These materials could comprise gravelly clay won from areas of completely

weathered to residually weathered greywacke within the quarry or competent moderately strong to

strong greywacke bedrock (i.e. silty sandy gravel).

Undercut below the approaches

Soft surficial layers can cause large settlements and also reduce stability. To provide a good quality

foundation for the approach formations, we recommend soft and surficial deposits are undercut

and replaced with structural fill. Based on the site investigations, an average thickness of about 1.0

m to 2.0 m undercut of topsoil, loose fill, clay and clayey silt may need to be undercut. Some

dewatering may be needed for undercutting and replacement construction.

Liquefaction mitigation below the approaches

The liquefaction assessment indicates that some layers of soil may be susceptible to liquefaction up

to depths of 23 m. Although the potentially liquefiable layers near the surface are generally thin,

liquefaction could lead to lateral displacement of the embankment, bearing capacity failure of walls

and settlement.

It is recommended that the ground is improved under the bridge abutments and other critical

structures that may be subject to lateral spreading. The ground improvement may extend to depths

up to 16 m to mitigate the risk of lateral spreading to acceptable levels. Ground improvement will

not eliminate subsidence completely. Subsidence of 100 mm to 125 mm may occur following a

strong earthquake. This level of subsidence is not likely to cause closure of the road for access, and

the road will be able to be readily reinstated after large earthquake events. We consider the

potential for differential subsidence and effect on approach fill and ductile walls such as reinforced

soils walls to be acceptably low.

Settlement of approaches

Static settlement is estimated to be in the order of 4% of embankment height assuming soft

surficial soils are undercut and replaced with structural fill. Clay layers up to 5 m thick could be

encountered at depths of about 10 m beneath some areas of the approach embankments. These

clay layers will take the longest time to consolidate and control the time it takes for completion of

settlement. We anticipate that 75 % of settlement will occur during construction but it may take

some 3 months to 9 months for complete settlement of the approach fills.



Unreinforced slopes

Stability analyses indicate that embankment slopes of 2H: 1V (26°) are suitable for embankments

up to 3 m high assuming any soft deposits are undercut and removed.

In design earthquake events (peak ground acceleration of 0.96g), displacements of 100 mm were

assessed using methods proposed by Ambraseys and Srubulov (1995).

Walls and reinforced slopes for approach embankments

There are several options for supporting the embankment where space is limited, these include:

• Inclusion of soil reinforcement to steepen slopes up to 1H: 1V,

• Soldier pile walls,

• Concrete cantilever walls,

• Vertical reinforced earth walls.

Reinforcement using geogrid to steepen slopes or construction of vertical reinforced earth walls are

recommended for scheme design as these structures are more ductile compared to other options

and can tolerate the moderate displacements that could occur from the expected static settlements

in earthquakes. Reinforced earth is also expected to be cheaper than the other retaining options.

Reinforced soil slopes are constructed like normal embankments, but incorporating HDPE geogrid

reinforcement layers. Reinforced slopes can be constructed without the need for permanent facing

for slopes as steep as 1H:1V.

The slopes and walls have been designed to the factors of safety and performance criteria as

specified in the Bridge Manual. The proposed earthquake design philosophy is to allow controlled

displacement of the reinforced embankments without failure through the reinforced soil block.



7.8.3 Pavement Subgrade

Fill Areas

New road pavements along the elevated east-west highway (SH1) will be formed on the fill

embankments. CBR (California Bearing Ratio) of 10 is assumed for selected good imported fill.

At Grade

The pavement for widening of the State Highway and other exit/entry from the State Highway and

local roads will be at grade. CBR of 3 to 4 is assumed for at grade pavements.

The groundwater table is at ground surface. It would be prudent to incorporate some subsoil drains

along the pavement, given the potential for water from surface run-off and leakage or breaks in

services.

The ground conditions at subgrade level are medium dense silty sand which will generally provide

a good subgrade for the new pavement. Given the fill and alluvial origin of the ground, looser sand

and weaker fine grained layers or lenses may be present, and provision should be made for

undercut and replacement of such layers with compacted sandy gravel. The silt content of the

ground leads to variability in its strength-deformation properties and therefore uncertainty in

pavement performance.

Additional in situ CBR or other strength-deformation tests such as Benkelman Beam tests are

normally carried out during detailed design and construction, after the scheme alignments and

road form options have been finalised. Such tests are recommended as they would provide design

parameters for detailed design and enable the risks related to the subgrade for the pavements to be

proactively managed during construction. Based on the description and observation of the ground

in trial pits and boreholes, a subgrade CBR value of 3 to 4 is proposed for the preliminary design of

the pavement.



7.8.4 Geotechnical Risk and uncertainty for Construction

The key risks affecting cost and time for construction of the bridge include:

• Artesian pressure effects for piling - Large diameter bored piles are recommended for the

bridge foundations considering the geotechnical issues. Large piles in artesian pressures can be

constructed with deeper and or telescopic casing or temporarily reducing the groundwater

pressures by drilling adjacent boreholes.

• Effectiveness, extent and cost of ground improvement.

• Amount of undercut - The undercut to remove any soft and loose materials underneath the

approach embankments is estimated to be 1.0 – 2.0 m based on available information. This

may be deeper in localised areas and may impact the construction programming and cost.

7.8.5 Recommendations

The following recommendations are made:

• Reinforced Earth Walls are formed at abutments using selected fill materials. Ground

improvement is recommended to alleviate liquefaction issues in the areas of the abutments.

• To address site specific conditions large diameter bored piles are recommended to support the

bridge. Subgrade CBR value of 4 is used for preliminary pavement design, subject to additional

in situ CBR and / or Benkelman Beam testing during design and construction for at grade

pavements.

• During detailed design more specific investigations should be considered to refine the design of

specific elements of the project.

7.9 Figures

The figures below show a geological cross section through the Project area and a map showing the

location of site investigations.



Figure 1- 26: Geological Cross Section



Figure 1- 27: Site Investigation Locations



8 Pavement and Surfacing

A preliminary design has been undertaken to identify the cost required to construct new road

pavements and tie into the surrounding pavement systems. The design completed to date has been

conservative and will be considered in more detail through detailed design.

8.1 Traffic Assumptions

For the purposes of pavement design traffic volumes from the Basin Reserve transportation model

for 2016 were used.

Figure 1- 28: Basin Reserve 2016 Traffic Volumes

It is assumed the percentage of heavy vehicles was 5% (based on count data), with a growth rate of

4.3%.

Design equivalent standard axles (DESA) were calculated to be:

• SH1 Westbound, Approach to Bridge: 4.32 x 107

• SH1 Westbound, Bridge: 4.02 x 107

• SH1 Westbound, West of Bridge: 5.08 x 107

• SH1 Eastbound: 3.37 x 107

• Local Roads Around Basin Reserve: 2.77 x 107

SH1 Westbound: Approach

to Bridge: 31 200 vpd

SH1 Westbound: Bridge:

29 000 vpd

SH1 Westbound: West

of Bridge: 36 700 vpd

SH1 Eastbound:

24 300 vpd

Local Roads around Basin

Reserve: 20 000 vpd



8.2 Pavement Assumptions

The following subgrade CBRs have been assumed (based on the 2011 geotechnical investigations):

• SH1 Westbound, Approach to Bridge: Subgrade CBR = 4%

• SH1 Westbound, West of Bridge: Subgrade CBR = 4%

• SH1 Eastbound: Subgrade CBR = 2%

Pavements shall be designed in accordance with the Austroads Pavement Design Manual and the

New Zealand Supplement.

8.3 Pavement Design

A preliminary pavement design has been done for the purposes of preliminary costing. The current

design is expected to be conservative and will be optimised during detailed design based on more

extensive geotechnical knowledge. Any optimisation will reduce the overall cost.

The proposed pavement design is a structural asphalt pavement as illustrated below:

Figure 1- 29: SH1 Westbound Approach to Bridge

The pavement design will be developed further through detailed design (and construction) based

on further understanding of the CBR and the whole of life costs.

8.4 Road Surfacing

The existing and proposed surfacing types are shown on the drawings included in Appendix A.

The NZTA have advised that any surfacing type that complies with the NZTA’s specifications for

friction will be acceptable. The Road Safety Audit in February 2012 highlighted that a high friction

surface might be required on the bridge curves to meet the standards assumed in Section 3.3.

Noise modelling and mitigation workshops have highlighted that the use of OGPA is strongly

desired from a noise mitigation perspective compared with the potential alternatives of noise walls

and building retrofit. As a result OGPA has been specified for all areas of SH1, with standard OGPA

35mm Mix 15

300mm Structural Asphalt

E = 3000 Mpa, v = 0.35

200mm Subbase

E = 250 Mpa, v = 0.35

Surfacing



in some areas and high stress OGPA on the bridge and the tight radii curves between Kent Terrace

and Paterson Street.

In areas of road that will be returned to WCC and surfacing works are required, a Mix15 AC is

proposed to tie in with the surrounding surfacing.

It should be noted that there will be a lag between the first coat seal and the application of OGPA

on Kent Terrace and on Ellice Street. The lag may be between 6-12 months, but given that this part

of the Project will be undertaken in the first phases then the final layer of OGPA will be applied well

before construction completion date. This delay will prevent premature cracking of OGPA

(through settlement) of the surfacing that would result in increased cost and disruption during

repairs.



9 Stormwater

A Stormwater Design Philosophy was prepared during the Scheme Assessment phase of the

Project. It defines the proposed standards, assumptions and outlines the background behind the

stormwater design concept. The following information has been taken from that report and

summarises the proposed level of service and design parameters.

9.1 General Philosophy

The overall area of road surface within the Project will increase with the construction of the new

westbound bridge. The change to the area of road surface for the eastbound alignment is expected

to be negligible.

The extent of permeable surfaces will be increased significantly in the area between the Buckle

Street Underpass and Cambridge Terrace, and between Ellice Street and Paterson Street as a result

of the proposed landscaping works.

All of the stormwater runoff from the new sections of road (or equivalent) will be attenuated and

treated in the proposed rain-gardens. Rain gardens are an urban stormwater treatment measure

and also offer the potential to provide a number of other landscape and cultural outcomes. The

area around the Basin Reserve has historically been wet, and used to be a food gathering site for

local iwi. A stream still exists below ground (now in a pipe) running down the Kent/Cambridge

corridor. The rain gardens will provide a reference to this stream, a link to similar devices used in

Waitangi Park and an opportunity for a reference to the historic use of the area.

The rain gardens will be located at either end of the bridge before being piped into the existing

stormwater system running along Kent and Cambridge Terraces.

9.2 Design Standards

The detailed design of the stormwater system will comply with the Stormwater Treatment Standard

for State Highway Infrastructure, the NZTA (2010).

9.3 Proposed Level of Service

On application of the design standards the following outcomes will be achieved:

New State Highway/Local

Arterial Road

Alterations to other roads

Road drainage2

Minimum of 2m width of road to be

passable3 in a 1% AEP storm event.

Minimum of 2m width of road to be

passable3 in a 5% AEP storm event.

2 These are aspirational levels of service. It should be noted that this project’s influence on the City’s drainage system is limited to a very local area and the overland flow path for a large part of the City (including Newtown and Brooklyn) drains through the site of this project. Without increasing the scope of the project to include upgrading the pipework from the Basin Reserve to Wellington Harbor, these aspirational levels of service may be compromised. 3 Highway surface Drainage, the NZTA, 1977



New State Highway/Local

Arterial Road

Alterations to other roads

Treatment of road

runoff

It is proposed to treat a road surface area, equivalent to the increase in

impermeable road surface. However where the opportunity exists,

additional road surfaces will be treated where practicable. In summary

there will be a net decrease in untreated road runoff entering the WCC

stormwater system.

Attenuation (storm

peak discharge

control)

For the critical duration storm event for the whole catchment; 50%, 10%

and 1% flows to be attenuated to 80% of pre road construction flows for an

area equivalent to the increase in impermeable surfaces.

9.4 Design Parameters / Assumptions

The following parameters / assumptions have been used for the preliminary design undertaken:

Climate change As the midrange of the MfE guidance to the year 2090, this is an additional

16.8% of rainfall for the 1%AEP storm event.

Stream channel

erosion control

Discharge is to a piped system, which is not prone to erosion. No erosion

control is necessary.

Attenuation (storm

peak discharge

control)

There are flooding issues downstream in the piped system; and the Project

location is in the upper half of the whole catchment when considering time

of concentration.

Climate change provision to be incorporated in post construction flow

estimates.

Treatment of road

runoff

Treatment to the NZTA requirements (which are an evolution of the TP104

treatment requirements, referred to in NZWERF’s “On-Site stormwater

management guide” which is referred to in WCC COP for “alternative

solutions”). This is a Best Practicable Option approach. The NZTA

treatment requirements are defined in their Stormwater Standard5.

From the NZTA Stormwater Standard6, the water quality event is defined

between 17.5 and 20mm over 24 hours (before allowing for climate change).

We propose 19mm for this stage of design.

Road surface

(Road drainage)

Maximum pavement water depth

4mm in a 10 minute, 50% AEP

storm event

No specific objective

Kerb and channel The site is highly constrained so there will be no significant shoulders

4 TP10, Stormwater Management Devices: Design Guidelines, Auckland Regional Council (ARC), 2003 5 Stormwater Treatment Standard for State Highway Infrastructure, the NZTA, May 2010 6 The NZTA stormwater guidance document defines the Water quality event as the 90th percentile rainfall event. From Appendix A of the NZTA stormwater guidance document the 90th percentile rainfall event along the project length varies between 17.5 and 20mm over 24 hours; we have adopted 19mm throughout (not including climate change)



with catchpits

(Road drainage)

Keep water channel flow, to a

maximum of 4mm at the edge of the

trafficked lanes in a 10% AEP storm

event

No specific objective to keep channel

flow out of trafficked lanes

In a 10 minute 1% AEP storm event, at least one lane is to remain passable.7

Where possible, stormwater flows are to be kept on the bridge deck and

discharged above the rain gardens.

Where the on deck channel capacity is exceeded, consideration should be

given to the use of an Envirodeck type system rather than grates and hanging

pipes under the bridge deck. In determining the best solution consideration

of operational impacts will be assessed.

Pipework

(Road drainage)

Catchpit leads and mainline pipework designed for the 10 minute, 10% AEP

storm event flows.

Pipe work to be designed for the 10 minute, 1% AEP storm event flows where

no secondary overflow path exists.

Climate change to be applied to all flows.

Pipework to have a design life of 100 years and designed to HN-HO-72

loadings

Raingardens The raingardens will provide the attenuation and treatment for the Project.

Physical parameters:

The attenuated volume is generally restricted to 300mm deep.

9.5 Construction Stormwater Treatment

Sediment and Erosion Control (E&SC) activities carried out during construction will comply with

the GWRC’s Erosion and Sediment Control Guidelines for the Wellington Region and the NZTA’s

Draft Erosion and Control Standard for State Highway Infrastructure and Draft Field Guide for

Contractors. The E&SC plans are live documents intended to be updated by the Contractor to

become part of the Contractor’s Environmental Management Plan (CEMP).

7 “Passable” is defined as 100mm of water depth (the NZTA 1977) with a velocity not exceeding 2m/s.



10 Structures

10.1 Bridge

10.1.1 General

The Project will provide the desired grade separation of the SH1 westbound traffic from the other

traffic. The bridge involves construction of a multi-span structure within the urban environment

and in close proximity to the historic cricket ground of the Basin Reserve.

The design statement during the Scheme Assessment phase sets out the design standards, and

factors which influenced the design. The following is a summary of the key design requirements.

10.1.2 Design Standards

The NZTA Bridge Manual, Second Edition 2003 and the material design standards specified

therein define the general design criteria to be adopted for the structure. This includes the June

and September 2004 amendments and the Provisional Amendment dated December 2004. Where

the Bridge Manual or the associated material standards do not cover the specific design issues the

appropriate Australian Standard or a British version of the Eurocodes are referenced.

10.1.3 Design Constraints

The design constraints identified for the bridge are as follows:

• The structure is located within close proximity to of the sea (within 1 km) and will require

appropriate precautions to achieve the required durability.

• The location has high seismicity and is within close proximity to the Wellington Fault.

• The bridge is categorized as an Importance Level 3 structure for which the design earthquake

return period at the ultimate limit state is 2500 years.

• The design life will be 100 years.

• Numerous existing underground and above ground utilities will need to be preserved or

diverted. The design is to be developed to ensure that the existing stormwater culverts

running along Kent and Cambridge Terrace will not need to be modified or disturbed as part of

the Project.

• Urban design requirements which will influence the form, materials and finishes of bridge

structures given the urban environment (further information on the urban design

requirements can be found in Technical Report 3: Urban and landscape Design Framework).

• Construction of the bridge close to residential areas that will place restrictions on construction

noise and vibration limits.

• Construction over existing roads requiring construction methods that minimise/avoid road

closures.

10.1.3.1 Vertical Clearances

The minimum required vertical clearances are as the following:

• 6.1m headroom over all crossed roads with an exception of the Hania Street and Ellice Street,

which provide local access only and where the minimum headroom should be at least 4.9m,



• 2.4m at any bridge location to allow for pedestrians/cyclist routes and access.

• The 6.1m minimum will provide sufficient clearance for overhead trolley cables and any light

rail components that may be required in the future.

10.1.3.2 Horizontal Clearances

The proposed bridge is required to provide clear spans over the following routes:

• Pedestrian/cyclist routes between City / Mount Victoria and Adelaide Road,

• Realigned Paterson Street (eastbound heading to Mount Victoria Tunnel),

• Hania Street and Ellice Street,

• Kent and Cambridge Terraces,

• Buckle Street turn into Cambridge Terrace.

The position of bridge piers has been designed to allow for clear spans over the above mentioned

routes as well as the sightlines required along these routes. In particular, sightlines along the inner

side of the corners from Buckle Street to Cambridge and Ellice Street to Paterson Streets impinge

on available positions for the substructure.

10.1.4 Bridge Form

Based on the road alignment and topography, the most appropriate form of structure is a low-lying multi-span structure. From an urban design, structural, geometric and WCC perspective a continuous structure of near constant depth was preferred.

The Project team decided early in the design process that a “feature bridge” was not appropriate as it would distract from other significant landmarks in the vicinity. Structural types where the bridge deck is supported from above (i.e. cable –supported, truss-supported or tied arch) were also not appropriate for this location and span arrangement. It was therefore decided that for this location the bridge should seek to be as slender as possible to reduce the visual impact.

Precast concrete beams were deemed to be unsuitable due to the size of the spans, tight curvature, substantial torsional demand, poor aesthetics and poor provisions for a continuous structure.

Working with the urban designer, architect, visual effects specialist and other members of the

Project team it was identified that a concrete single box girder was the most appropriate form of

bridge. The design has been developed on this basis with a particular focus given to those who

walk, cycle and drive under and around the bridge.

The bridge design and proposed architectural treatments are illustrated in Volume 5: Plan Set.

10.1.5 Design Requirements

10.1.5.1 Edge Protection

The barriers along the roadway are required to be Performance Level TL-5 with minimum 1.1m

high (0.82m solid concrete with metal rail to 1.1m) in accordance with the Bridge Manual. The

barriers along the outer edge of the walking/cycling facility are required to be 1.4m high for cyclist

protection.



10.1.5.2 Vehicle Impact Loads

All unprotected bridge supports located within 5.0m clear distance from the edge of the nearest

carriageway are required to resist a nominal equivalent static load of 1000kN applied at an angle of

ten degrees from the direction of the centreline road passing under the bridge. The load shall be

applied 1.2m above ground level.

10.1.5.3 Materials and finishes

The choice of materials and finishes for bridges and retaining walls is being developed in

conjunction with the urban design team and takes account of whole of life costs. The current

proposal is to use concrete for all bridge components as this provides desired appearance quality

with good durability for the range of spans required. It may be possible to utilise other materials

providing the overall appearance of the structure does not differ significantly from that shown as

part of the AEE submission. Appropriate measures will be considered and incorporated in the

design to prevent or discourage graffiti on surfaces which are accessible by members of the public.

10.1.5.4 Drainage

The drainage design needs to ensure that surface water will not be able to fall freely from the bridge

deck. The bridge deck needs to have sufficient transverse and longitudinal falls to enable its

dewatering. Where the design requires a surface water drainage system, the system is to be

provided with access chambers for inspection and rodding of drainage runs. The drainage system is

to be sufficiently robust to withstand damage during cleaning and to be resistant to commonly

occurring spillage.

It is desired that storm water drains are not visible from below the bridge. As far as practicable the

openings through the bridge deck and drains located under the bridge soffit should be avoided due

to negative visual and durability impacts.

Drainage water from the bridge deck is not to be discharged into the drainage layer behind

abutments. All bridge abutments and earth retaining structures will be provided with a positive

drainage system (one with adequate fall to enable water to flow away) to the earth faces. Such

drainage systems design shall include provision for future access and cleaning through rodding.

10.1.5.5 Bridge Retaining Walls

Retaining walls will generally be mechanically stabilised earth walls as described in the

Geotechnical section. Walls will be designed in accordance with the NZTA Bridge Manual.

10.1.5.6 Provision for Services

Through meetings with the NZTA, two 100mm diameter ducts for Active Traffic Management

System cables and one 100mm diameter duct for the street lighting have been identified to be

carried on the bridge. No other services have been identified to be carried on the bridge at this

stage.

Wherever possible, service ducts should be accommodated within the footways/raised verges of the

bridge deck. Service ducts should not be integrated into structural concrete members.



Separate access chambers should be provided in the design at each end of the structure for service

ducts and should be designed to curtail the passage of water along ducts.

There is a large number of existing under/over ground services in close proximity to the bridge site.

The service providers have been requested to confirm the exact number and positions of the

services and to provide limits for the construction activities when working in proximity to the

services. This consultation is on-going. The design and construction methods will need to take this

into account.

10.1.5.7 Expansion Joints and Bearings

The bridge structure is designed to minimise the use of expansion joints and bearings in order to

reduce long term maintenance requirements and road noise. The current design has bridge joints

located at each bridge abutment only. As a minimum, joints on the vehicle lanes should not be used

within the 50m section of the bridge spanning between Kent Terrace and Ellice Street. Where

appropriate a monolithic connection between the super-structure and sub-structure will be

adopted.

The form of joints used at either abutment will be chosen to meet the required expansion of the

structure whilst minimising potential for adverse noise and maintenance. Noise effects of bridge

joints are considered in TR5.

10.1.5.8 Bridge Foundations

Bridge foundations will be designed in accordance with the Bridge Manual to provide stability and

control settlements. Piled foundations will be provided for all bridge supports. Unsuitable

soft/loose soils that occur below bridge abutments and approach embankments will be removed

and replaced with granular material to mitigate differential settlement between the bridge and the

approach.

10.1.6 Future Design Development

There are a number of design areas that need to be considered further through detailed design and

construction:

• Through detailed design (and construction) the piers are expected to move between 0-3m as

the detailed design develops to take into account more information about existing services etc.

In some locations the piers can only move a very small amount (if any) due to other constraints

on their location.

• The exact form of the piers will be developed through detailed design. The current proposed

pier shapes are based on a number of drivers that are identified in Technical Report 3: Urban

and landscape Design Framework.

• The use of kerbs on the bridge adjacent to the barrier.

10.2 Building under the Bridge

The preferred treatment of the space under the bridge between Kent Terrace and Hania Street is a

building integrated with the bridge which provides a positive street edge. A number of options



were considered including a park space, vehicle parking and other sizes of structures. This is

discussed further within Technical Report 3: Urban and landscape Design Framework.

Work has been undertaken to assess the feasibility and technical requirements for the construction

and use of such a building. The following is a summary of the key factors that need to be

considered:

• Fire Risks;

• Noise and Movement;

• Inspection and Maintenance;

• Earthquake Performance;

• Structural Capacity;

• Drainage and;

• Falling Objects.

Appendix A contains a proposed specification that will inform the construction and operation of

the building to mitigate the risks raised in the list above.

10.3 Basin Reserve Northern Gateway Building

Mitigation is required to screen the visual effect of the Bridge within the Basin Reserve. The

preferred mitigation is the construction of a new Northern Gateway Building. A number of

different structural forms were considered before this form of mitigation was arrived at, including a

screen element and buildings of differing scales. This is discussed further within Technical Report

3: Urban and landscape Design Framework.

As part of the cost estimate of the preferred option for the building the following points were

identified:

• Shallow foundations would not be suitable and the building should be piled to mitigate the

variable conditions and possible differential settlement.

• The piling options suit larger diameter bored cast in place (>600mm) piles rather than precast

driven piles.

• Free water and aquifers inferred are at shallow and mid depths depending on location.

• The ground conditions are better closer to the RA Vance Stand on the west and piles are

needed to be about 15m depth in this area (under the main part of the building).

• The conditions get less favourable as you move toward the east embankment. The bedrock

dips gradually with piles needing to be up to 20-25m depth in this location.



11 Urban and Landscape Design

The design principles for urban design are discussed within Technical Report 3: Urban and

Landscape Design Framework (ULDF). The ULDF also provides a summary of factors that have

influenced the design development.



12 Lighting

12.1 Street Lighting

The section of SH1 from the Basin Reserve to Willis Street is classified as a high volume National

State Highway in an urban area. Pole heights, spacing and locations will be designed to comply

with Australian/New Zealand Standard – AS/NZS 1158.0:1997: Assessment of the standard

suggests the requirement for Road Lighting Category V2 with a possibility of dimming to V3 at

times of low vehicle counts. This lighting category assessment considers the following factors:

• Vehicle numbers;

• Road designation (e.g. Major arterial)

• Traffic composition (motorised and non-motorised users)

• Pedestrian and cyclist numbers

• Vehicle speed

• On street parking

• Traffic generation from adjacent properties; and

• Ambient lighting.

12.2 Design Options Considered

A number of different options of pole heights and spacing were considered. Figure 1- 30 provides

an example of two of the options considered.

Figure 1- 30: Example of comparison of different light pole spacings

Low-level lighting on the bridge was considered in order to improve the bridge aesthetics by

removing the need for the light poles. However these lights would not provide adequate

illumination for the pedestrians on the bridge and would require supplementary lighting for the

pedestrian/cycle path. The low level lights may also have been a potential target for vandals.

Based on feedback from the urban design and visual impact specialist it was decided to provide

regular spaced poles that were lower in height. The lanterns are lower (8m) than a typical 10-12m

light pole to minimise the visual impact of the poles on top of the bridge. The spacings are also

closer than typical street lights due to the reduced height and are set out to respond to the rhythm

of some of the structural elements of the bridge such as the cantilever ribs and span lengths.



12.3 Current Design Proposal

The proposed layout of lighting is shown on the drawings.

The layout has been developed on the assumption that LED lighting is used. A decision on whether

to use LED lighting or more conventional lighting will be made based on a value engineering

assessment at the detailed design stage. LED lighting is more efficient to run and results in reduced

spill lighting and lower running costs; however the capital costs are higher.

The proposed street lighting arrangement includes:

SH1 Westbound: 8m poles at 21m centres from the start of the tunnel portal to where the

pedestrian/cycle bridge separates from the main structure (layout offset

from pole on central pier between Kent and Cambridge Terrace).

8m poles at 21m centres from where the pedestrian/cycle bridge separates

from the main structure through to Mount Victoria Tunnel portal.

8m poles at 15m centres on the pedestrian/cycle bridge / path from the main

bridge to Saint Joseph’s Church.

SH1 Eastbound: 8m poles at 21m centres from Kent Terrace to Mount Victoria Tunnel portal.

Paterson Street: Existing Street Lighting Retained.

Dufferin Street: Existing Street Lighting Retained.

Rugby Street: Existing Street Lighting Retained.

Sussex Street: Existing Street Lighting Retained.

Sussex Street: Existing Street Lighting Retained.

Cambridge Terrace: Existing Street Lighting Retained.

This design is based on the use of 36 Watt lights (20 LEDs) for the pedestrian / cycle path with 104

& 154 Watt lights (60 & 90 LEDs) proposed for the roads.

12.4 Design Outcomes

The preliminary design modelling indicates that the spill light will only exceed 10 lux on two

buildings; Saint Joseph’s Church and one of the Saint Marks School buildings. 10 lux is a rule of

thumb lighting value that generally should not spill over onto private property. Cowls could be

attached to lanterns in those areas to reduce the spill light; this will be investigated further at

detailed design. The WCC District Plan rules for the Central Area provide rules for permissible light

spill, and will be considered at detailed design.

The urban design and visual assessment specialists have raised concerns about the number of

lighting poles in the area around the corner of Kent Terrace and Ellice Street. All of those shown in

the Scheme Drawings below are required to adequately light the road and surrounds.

Consideration should be given at the detailed design phase to ensuring that these poles are not



additional to the poles required for the trolley bus wires and where possible the; light poles are

located onto the bridge soffit or similar to minimise visual clutter.

12.5 Architectural Lighting

The drawings propose a lighting strategy for the Project and include the following aspects of

architectural lighting:

• Lighting within the building under the bridge.

• Low level feature / element lighting between the Buckle Street Underpass portal and

Cambridge Terrace.

• Feature lighting to piers and abutments.

• Feature lighting to lower soffit of bridge structure.

• Feature lighting to sides and cantilevered ribs of bridge superstructure.



13 Services and Utilities

Information on utilities within the study area has been supplied by the utility owners and sourced

from a GIS database. Plans are indicative only and exact locations will be confirmed at a later stage.

The study area is in an urban environment and hence coverage of utilities is high. As the

investigations progress a better understanding of the utilities in the area and the extent of impact

will be gained. Discussions with utility owners are on-going.

Table 1- 3: Existing Utilities and Services Identified

Road

Over

Head

(OH)

Power

Under

Ground

(UG)

Power

Comms Water Sewer Storm

Water Gas

Trolley

Bus

Adelaide Road Y Y Y Y Y Y Y Y

Buckle St Y Y Y Y Y Y Y Y

Brougham

Street

Y - Y Y Y Y - -

Cambridge

Terrace

Y Y Y Y Y Y Y Y

Dufferin Street Y Y Y Y Y Y Y Y

Ellice Street Y Y Y Y Y Y Y Y

Hania Street Y Y Y Y Y Y Y -

Kent Terrace Y Y Y Y Y Y Y Y

Paterson Street Y Y Y Y Y Y - -

Rugby Street Y Y Y Y Y Y Y Y

Sussex Street Y Y Y Y Y Y Y Y

Tasman Street Y Y Y Y Y Y Y -

Tory Street Y Y Y Y Y Y Y -

Basin Northern

Gateway

- Y - Y Y Y Y Y

At this stage, the following services have been identified as having potential conflict with the

proposed works:

13.1.1 Telecommunications Services to be relocated - Telecom

• Large capacity Fibre middle of Kent / Cambridge

• Large capacity Fibre Dufferin / Ellice St



13.1.2 Telecommunications Services to be relocated - TelstraClear

• None Expected

13.1.3 Telecommunications Services to be relocated - CityLink

• 24 Fibre Aerial (12mm)



13.1.4 Power Services to be relocated - Wellington Electrical

• 2 x UG 33kV on Paterson St

• 400kV OH to UG Kent/Ellice

• 400kV OH to UG Buckle/Cambridge

• 400kV OH to UG Dufferin/Paterson

• UG LV (400V) cables Dufferin / Ellice St

• UG HV (11kV) cables Dufferin / Ellice St

• UG DC Cables Ellice / Hania St

• Public Light Poles Kent/Ellice/Dufferin St

• Public Light Poles Buckle / Cambridge

• UG DC Cables Basin Northern Gateway

13.1.5 Power Services to be relocated - Wellington Cable Car Ltd (WCCL)

• OH lines & pole relocations, WCCL have provided a CAD drawing of the OH lines on a copy of

the Project drawing which indicates that the position of the OH lines will not need to be

adjusted from what is currently in place. However, new poles will be required in a number of

locations.

13.1.6 Gas Services to be relocated - PowerCo

• 24" Dia Cambridge / Ellice

• 50mm Polyethylene Dufferin / Ellice

• 100mm Polyethylene Dufferin / Ellice

• 50mm Basin Northern Gateway

• 100mm Basin Northern Gateway

13.1.7 Water Services to be relocated - WCC

• Rising Water Main Buckle / Cambridge (unknown dia)

• Rising Water Main Basin Northern Gateway (unknown dia)

• Water Main Dufferin / Ellice (unknown dia)

• Water Main Kent/ Ellice (unknown dia)

13.1.8 Stormwater Services to be relocated - WCC

• 1.8m Ø Storm water pipe Cambridge Terrace

• 1.0m Ø Storm water pipe Cambridge Terrace



• (unknown dia) Paterson St South side

• (unknown dia) Ellice / Dufferin St

13.1.9 Sewer Services to be relocated -WCC

• Sewer from church (unknown dia) Ellice / Dufferin St

• 200mm Ø Sewer Basin Northern Gateway

The known existing services are shown on the Volume 5: Plan Set. Services will not be relocated

other than those that come into conflict with the design. The places to which the services are to be

relocated will be agreed with the NZTA, WCC and the asset owner.



14 Noise

The design of the bridge and other road network alterations has been an iterative process that has

been informed by noise assessment and the potential to mitigate noise effects. Therefore the

current design incorporates the viable noise-mitigating features.

Further discussion on the options considered is included in Technical Report 5: Assessment of

noise effects.

The key outcome through collaboration between the design team and noise specialist has been to

meet the required standards through treatment at the source (through quieter road surfacing)

rather than using visually intrusive noise barriers.



15 Wind

A wind assessment has been undertaken to consider the effects of the proposed Basin Bridge on

wind conditions for different users on and around the structure. The following sections consider

the potential effects on:

• Pedestrians and cyclists on the bridge

• Vehicles on the bridge

• Pedestrians under the bridge

• The Basin Reserve itself.

15.1 Existing Wind Conditions

Strong winds over Wellington City are dominated by wind flows from the north to north-westerly

and south to south westerly sectors. Although northerly winds occur more frequently than

southerly winds for light to moderate winds, the highest wind speeds occur with about the same

frequency for both direction sectors. Strong southerly winds tend to be noticed more by

pedestrians than strong northerlies because it is often also raining and cold.

Pedestrian level wind conditions during strong winds in the area around the Basin Reserve,

particularly around the northern end where the bridge is planned, are determined by the

combination of effects created by (1) the surrounding topography, (2) the alignment of the streets

and open areas to the prevailing wind flows, and (3) the sizes, heights and locations of the

surrounding buildings.

The Basin Reserve sits in a valley, which tends to channel wind flows along it. This effect is

increased by the alignment of the relatively wide open spaces of Adelaide Rd and Kent and

Cambridge Terraces to the prevailing winds, and the open area of the Basin Reserve itself. The

buildings in the immediate area which can channel or deflect wind flows are mostly low-rise blocks,

with a scattering of taller buildings. One of these taller buildings sits on the corner of Kent Terrace

and Ellice Street (Grandstand Apartments), recently being more exposed to southerly winds by the

removal of the neighbouring buildings to the south.

15.2 Effects of the Proposed Scheme on Local Wind Conditions

Changes in urban situations, including the addition or removal of buildings or structures,

significant changes to existing buildings or structures, or significant landscaping, typically have the

greatest impact on wind conditions by changing the areas that are exposed to direct wind flows, or

by forcing wind flows to take other paths. In this case the major physical changes relating to effects

on wind are the bridge, the adjoining pedestrian/cycle bridge, the landscaping, the proposed

building under the bridge on the corner of Kent Terrace and Ellice Street and the proposed new

Northern Gateway Building. The following sections discuss the impact of these changes on the

areas described earlier, and suggest potential options for mitigation where these are considered

appropriate.

15.2.1 Wind Effects – Pedestrians and Cyclists on the Bridge

Wind conditions on the bridge will vary along its length. At either end, where the bridge lands,

wind conditions will be similar to those described above, i.e. determined by the surrounding



topography, buildings and landscaping. Wind gust speeds in the central section of the bridge are

likely to range up to extremely high levels (greater than 25m/s). The orientation of the bridge to

the prevailing winds means that pedestrians and cyclists will be exposed to wind flows from side-

on, for which they are less prepared.

Given the expected wind conditions on the bridge, two alternative approaches have been suggested

that would help to avoid pedestrians and cyclists experiencing wind conditions that are unpleasant

or dangerous at times. The first of these would be to incorporate higher barriers along the northern

edge of the pedestrian/cycle bridge, particularly in the central area over Kent/Cambridge Terrace.

Typically, these would need to be either solid or porous (20% to 40% porosity) barriers around 2m

or more high. Solid barriers provide greater shelter in the areas immediately downstream, while

porous barriers are generally more effective over a greater distance downstream.

The second approach is to ensure alternative routes for pedestrians and cyclists are available, and

that signage is used to alert users to these routes, and to their suggested use in windy conditions.

The Project team following wider consideration of the possible effects of these two solutions has

chosen the latter option (signage to alert users to alternate routes, and recommend their use in

windy conditions). The primary reason for this is the negative visual effects associated with a tall

screen structure on the bridge. Consideration may be given (at detailed design) to providing

electronic warning signs for pedestrians at either end of the bridge using a wind measurement

device.

15.2.2 Wind Effects – Vehicles on the Bridge

The main risks to vehicles from wind typically occur in strong cross winds. The risks are greater for

high-sided vehicles (e.g. light trucks that are lightly loaded) and motorcycles. Effects can range

from causing tracking variations to complete overturning. The more at risk vehicles can experience

these effects when gust wind speeds range up to 25m/s or higher, and these wind speeds do occur

from time to time in Wellington (though not often). Accordingly, vehicles crossing the bridge will

experience these conditions at times during any typical year. However, the level of risk is

considered to be relatively minor, given the fairly short distance of greater exposure towards the

centre of the bridge, the posted 50km/h speed limit, and the relatively infrequent occurrence of

such wind conditions. Variable Message Signage (VMS) can be used to mitigate this potential risk.

15.2.3 Wind Effects – Pedestrians under the Bridge

There are four aspects of the design that need to be considered in terms of their potential to affect

pedestrian wind conditions under the bridge. These are the bridge itself, the landscaping that is

proposed, the Northern Gateway Building and the new building for the corner of Kent Terrace and

Ellice Street.

The bridge is elevated, and the current design has a relatively slim vertical profile. Accordingly, the

area that is exposed to direct wind flows is quite modest, and being elevated, is well away from

pedestrian areas. Accordingly, the bridge will have little effect on wind conditions in the area under

the bridge apart from the potential for small localised increases in wind velocity around the bridge

support columns.

A mix of vegetation landscaping is currently proposed, in the form of trees and smaller shrubs and

plants. Landscaping will not make wind conditions worse at any locations in this area. Once the



landscaping is established and reasonably dense there is the potential for it to be beneficial for

wind conditions, by breaking up wind flows and providing shelter.

The area immediately adjacent to the intersection of Kent Terrace and Ellice Street is currently

vacant, where the earthquake prone buildings were removed. This has increased the exposure of

the neighbouring multi-storey building to direct southerly wind flows, making the southwest

corner of this building a windy location. The proposal to include a building under the bridge on this

corner site would help to significantly improve wind conditions around this corner, breaking up

vertical wind flows off the neighbouring building, providing shelter and a better transition around

the corner for pedestrians. The inclusion of additional porous screening for visual reasons on top of

this building would also be beneficial. The inclusion of these elements in the design is viewed as a

positive outcome for reasons of wind effects.

15.2.4 Wind Effects – The Basin Reserve

In southerly wind conditions the bulk of the proposed Scheme Design, including the bridge, is

downwind of the Basin Reserve. Accordingly, it will have no impact on wind conditions in the Basin

Reserve in southerly winds. However, the proposed new Northern Gateway Building sits on the

perimeter of the Basin Reserve. While the height, bulk and general design of the new stand will

have little impact on wind conditions, the building does also incorporate significant openings at

pedestrian level, in the form of entrance gates. The current open design of these gates will allow

southerly wind flows to impact on the immediately adjacent pavement area in Buckle Street. Wind

speeds are likely to increase in this relatively localised area. While the resulting wind speeds will be

typical of other locations in the surrounding area, there will be noticeable changes from what is

currently a sheltered region. One option to mitigate these effects would be to reduce the porosity of

the gates. They could either be made solid, or some degree of porosity could be retained to

maintain a visual connection. Typically, porosities of around 30-35% are considered to provide the

most overall effective shelter for areas downwind.

In northerly winds, the bulk of the design is only a short distance upstream. The only two elements

in the proposed scheme that could have an impact on the Basin Reserve are the elevated bridge and

the proposed new Northern Gateway Building. The only way the elevated bridge could impact on

wind conditions in the Basin Reserve is if significant additional wind flows are deflected down into

this area by the bridge. As the bridge is a minimum of 7.3m in the air (to base of soffit), and is

relatively slim in its vertical profile, the likelihood of this occurring is expected to be very small.

The height, bulk and general design of the new building will have little impact on northerly wind

conditions. However, the open design of the entrance gates underneath this new building will allow

northerly wind flows to penetrate through into the ground over this localised area. Spectators will

not notice any change in the amenity of this area as there is no seating that is affected. However,

players will be exposed to some increased wind flows in the area close to the gates, although the

wind speeds will be similar to many other parts of the ground. As is the case for southerly winds,

the effects could be mitigated by reducing the porosity of the gates.



16 Future Proofing

16.1 Wider Strategy

The Project is an integral part of both the RoNS and Ngauranga to Airport Corridor Plan. The

Project has been designed to provide a scheme which complements and operates effectively with all

of the other related projects identified in the RoNS, Corridor Plan and the Regional Land Transport

Strategy / Plan (RLTS & RLTP). Further details of the future proofing requirements for the

immediately adjacent projects are provided below.

16.2 Passenger Transportation Spine

One of the key objectives of the Basin Bridge Project is to facilitate the development of an improved

passenger transportation spine between Adelaide Road and Kent / Cambridge Terraces. The

current scheme removes a significant amount of traffic from the road network around the Basin

Reserve which allows for existing road space to be set aside for passenger transport usage. The

scheme drawings show a layout of bus lanes and priority which will operate effectively using the

current infrastructure and vehicles available (more detail on how this will work is provided in

Section 6.3, Transportation Design).

The project team for the Passenger Transport Spine Study have been provided with CAD drawings

of the project for tracking and clearances purposes and have confirmed that the options that they

are currently considering all fit through and around the bridge, i.e. the bridge does not constrain

public transport options being considered.

16.3 Inner City Bypass (Karo Drive and Vivian Street)

The NZTA has plans to upgrade / optimise the Inner City Bypass (ICB) to improve travel times and

reduce congestion. As of March 2012 a Project Feasibility Report (PFR) was being prepared for this

work. The PFR assesses a number of different intervention levels from minor lane widening to

three laning of SH1 in both directions with significant intersection improvements. The Basin Bridge

Project and the improvements to the ICB have been developed simultaneously and are

complementary.

16.4 Mount Victoria Tunnel Duplication

The design for the Basin Reserve has been closely coordinated with the proposed scheme to

duplicate the Mount Victoria Tunnel. The proposed posted speed limit through the duplicate

Mount Victoria Tunnel will be 50 km/h which will tie in with the 50km/h posted speed proposed

through the Basin Reserve.

The current design as shown on the scheme drawings connects to the existing Mount Victoria

Tunnel and as such connects into the existing sub-standard lane and footpath widths. Because of

width restrictions the second westbound lane travelling on the new bridge does not develop until

part way onto the eastern abutment. Following the duplication of the Mount Victoria Tunnel the

two eastbound and two westbound lanes will be amended from outside the church similar to the

indicative diagram below.



Figure 1- 31: Future connection to a duplicate Mount Victoria Tunnel

The latest information available on the tunnel duplication should be considered at detailed design.

16.5 Intelligent Traffic Systems (ITS)

Future proofing for ITS has been allowed for and two 100mm ducts with appropriate pull-pits and

associated infrastructure will be provided as part of the bridge structure as detailed in Section 4

Signs and Markings. New fibre optic cable will be provided in the bridge as part of the Project and

will connect to the fibre optic cable which currently runs through the Inner City Bypass to

Cambridge Terrace.



Appendix A – Proposed Design Requirements for the Building under the Bridge

It has been assumed that the two buildings that form part of the Project (the building under the

bridge, and the Northern Gateway Building) will be designed, operated and maintained to satisfy

all of requirements of the district plan, and the Building Code.

The following sections outline the specific requirements for each of the key risk areas in relation to

design, operation and maintenance of the building under the bridge. These requirements will be

considered further during the detailed design and construction.

Fire Risk

Ref Type Specification

OP1 Operational No storage of flammable materials / supplies (car showroom would

be acceptable).

OP2 Operational Any building use should have a minimum fire hazard category of 1

(as per Compliance Document for New Zealand Building Code

Clauses C1, C2, C3, C4Fire Safety).

DE1 Design A high-spec automatic fire suppressant system shall be installed

both inside the building and on the bridge soffit above the building.

DE2 Design The design of the roof of the building shall achieve a minimum Fire

Resistance Rating (FRR) of FRR 60/60/60.

(As per Compliance Document for New Zealand Building Code

Clauses C1, C2, C3, C4 Fire Safety).

DE3 Design Any of the bridge piers (and associated flashings) within close

proximity of the building shall achieve a minimum FRR of

60/60/60.

(As per Compliance Document for New Zealand Building Code

Clauses C1, C2, C3, C4 Fire Safety).

MA1 Maintenance Any maintenance work on either the bridge or building using

flammable materials in the vicinity of the building and bridge will

require a specific fire risk safety assessment prior to work

commencing and be approved by the NZTA.

Noise and Vibration


OP3 Operational Noise and vibration from the bridge and at-grade roads will be

identified as a base effect in any lease.

OP4 Operational The building shall not be used for the purpose of residential

habitation (e.g. sleeping).



DE4 Design No bridge expansion joints shall be placed within 50m of the nearest

edge of the building under the bridge.

DE5 Design The supports for the bridge and the building shall be designed to be

independent and allow for appropriate differential movement and

vibration.

MA2 Maintenance Any noisy maintenance and re-surfacing works on the bridge shall

comply with WCC’s Noise Policy and the NZTA’s Environmental

Policy Manual.

Inspection and Maintenance


OP5 Operational Access inside the building to inspect any piers within the building

shall be a requirement of any lease. Five working days’ notice will be

required prior to any non-urgent inspection works.

Short notice for access into the building will be required for any

urgent inspection works.

OP6 Operational Access inside the building to maintain any piers within the building

shall be a requirement of any lease. Twenty working days’ notice will

be required prior to any non-urgent maintenance works.

Short notice for access into the building will be required for any

urgent maintenance works.

DE6 Design A minimum of 1.2m vertical separation shall be provided between

the building roof (excluding parapets) and the bridge soffit to allow a

space for inspections and maintenance to take place.

DE7 Design The roof of the building would have to be relatively flat (and free-

draining) and designed to support loading that would be required

for inspections and maintenance (5KPa) at a minimum.

DE8 Design Independent secure access to the roof of the building would be

required (lockable permanent ladder would suffice).

2 No IP65 rated single phase power sockets shall be provided on the

roof of the building for maintenance purposes.

MA3 Maintenance Any tenants of the building shall be notified of any impending

maintenance work on the bridge or access to the roof of the building.

Earthquake Performance


DE9 Design The bridge shall be designed to the requirements of the NZTA bridge

manual (see Section 10.1).

DE10 Design Seismic separation shall be provided between the building and the

bridge to cater for design displacements for a design level return



period event.

DE11 Design The building shall be designed for a design return period event the

same as the bridge unless;

• The bridge piers are designed to resist any loading from the

building in the event of its collapse; or

• A detailed seismic assessment of both structures (bridge and

building) shows that the failure mechanism of the building will

place no additional load on the bridge structure.

Structural Capacity


OP7 Operational No structural modifications shall be permitted to the building

without the NZTA’s consent.

DE12 Design The building shall be designed to the requirements of AS/NZS 1170

except where otherwise required by this report.

DE13 Design The design of the building shall be approved by the NZTA prior to a

building consent being sought.

Drainage


DE14 Design The roof drainage shall be fitted with an appropriate filter to screen

any contaminants from the bridge structure.

DE15 Design All drainage on the bridge (above the building) shall be collected in

deck drains diverted to a collection point (sump or similar)

independent of the building.

The barrier and edge detail shall be appropriately detailed such that

there are no gaps for drainage from the bridge deck to permeate

through to drip on the building roof.

Opus International Consultants Ltd L7, Majestic Centre, 100 Willis St PO Box 12 003, Wellington 6144 New Zealand t: +64 4 471 7000 f: +64 4 471 1397 w: www.opus.co.nz

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