Download the Institue of Engineers in Ireland Presentation Paper on the N11 Ashford

The Institution of Engineers of Ireland

Civil Division

Jointly with the Roads and Transportation Society

Design and Construction of the N11 Newtownmountkennedy to Ballynabarny Road Improvement Scheme

(The Ashford Rathnew Bypass)

John Higgins BE, CEng, FIEI, FICE, FIHT, FCIArb, Consultant, Arup Consulting Engineers Adrian Duffy, BE, MEngSc, DipConLaw, CEng, MIEI, Associate Director, Arup Consulting Engineers

Duncan Cole, BA, BAI, CEng, MIEI, MICE, Project Resident Engineer, Arup Consulting Engineers John Crowley, BE, Project Manager, Morris-Sisk Consortium

Paper presented at University College, Dublin at Earlsfort Terrace on

Wednesday 20 October 2004 Abstract : This paper discusses the recently opened N11 Newtownmountkennedy to Ballynabarny Road Scheme, also know as the Ashford-Rathnew Bypass. Particular attention is paid to the design and construction of the earthworks, including 1.5m cubic metres of rock excavation, the unique family of bridges developed for the scheme, contractual arrangements and how they changed during construction, and the management of construction.

N11 Ashford Rathnew Bypass IEI Civil Division

20 October 2004 Page 1

1.0 Introduction Planning by Wicklow County Council for the N11 improvement scheme between the end of the Newtownmountkennedy Bypass and the straight on the N11 at Ballynabarny, south of Rathnew began in 1994 in earnest. In 1995 McCarthy& Partners and RPS were appointed by the Council to carry out the route selection process and to prepare an EIS for the preferred route. Newsletters were prepared and widely circulated by the Council in March of 1995, and February & December of 1996, as part of the public consultation process.

The EIS was published in June 1999. The CPO was approved by the Minister on 28 August 2000.

Arup Consulting Engineers were appointed in March 1999 to prepare detail design and contract documentation under the standard NRA Contract process and using the IEI 3rd Edition Conditions of Contract.

Prequalification of Contractors was undertaken in 2001 and following a tender competition in 2001, the Morris-Sisk Consortium, who had submitted the lowest conforming tender, were recommended for appointment. Work commenced on site in February 2002, with a prescribed time for completion of 36 months. The project was formally opened by Mr Seamus Brennan, Minister for Transport, on 27 September 2004. Even allowing for unavoidable delays and extensions of time due to exceptionally inclement weather the opening date was more than five months ahead of schedule.

The scheme involved the construction of 13.6 kilometres of dual carriageway through undulating rocky terrain with 5 interchanges, and 15 kilometres of ancillary and side roads (see Cover - Figure 1). While much of the new route for the dual carriageway went through green fields, the new alignment overlaps the old for almost 4 kilometres. The new route also crosses the Dublin Wexford railway line, two rivers and 10 side roads, requiring 13 bridges. From a construction standpoint the scale of the Earthworks required was the most significant element of the works. About 2.55 million cubic metres of bulk excavation was required, just over half of which proved to be rock. There were also some extensive areas with very poor marshy ground, which required large-scale ground replacement. The project also originally required about 0.5 million cubic metres of import of suitable material with a

corresponding volume of unsuitable material to be disposed off site. 2.0 Structures The scheme, although only 13.6km in terms of length of mainline, included a large number of structures due to the number of interchanges, proximity to the towns of Ashford and Rathnew, and existing ‘fixed’ obstacles such as the Vartry River and the Dublin Wexford Railway Line.

• 5 road overbridges • 5 road underbridges • 1 railway underbridge • 2 river underbridges • 3 major retaining walls • 5 cattle underpasses • 22 Culverts

This gave a total of 13 significant bridges and 30 other structures. 2.1 Preliminary Design Although the preliminary design of the roadworks to CPO/EIS stage had been carried out by Wicklow County Council, the preliminary design of structures had not been addressed prior to the publication of the scheme. The preliminary design of the structures was therefore included in Arup’s appointment, and was one of the first tasks that had to be undertaken. From the start, the natural beauty of the site provided a challenge to design the bridges so that they would each fit within the landscape. It was also immediately apparent that the way in which the mainline/minor road alignment sat within the existing topography, with dramatic cuttings and spectacular views over the landscape, would make the overbridges visually important. In recognition of the visual prominence of the structures, Arup appointed Murray O’Laoire Architects as sub-consultants to advise on bridge aesthetics.

Starting out on the preliminary design, it was clear that there were a considerable range of site parameters that would have to be addressed in the design: • The 2 overbridges at either end of the

scheme would be elevated in striking rock cuttings, and would act as visual ‘book-ends’ to the project;

• The central section of the scheme is set in undulating topography, with variable ground conditions;



• Structure 4, the railway bridge, would present the usual restrictions on construction over live railways, requiring railway possessions etc.;

• Structure 3, Cuckoo Lane Underbridge, would be located where the mainline would be on a 18 m high fill embankment;

• Structures 8 and 12, Mill Road and Timmore Lane Overbridges, would have to follow the existing road alignments crossing the mainline at high skew, and in the case of Mill Road Overbridge, on a horizontal curve.

It was decided that the best approach regarding constructability and visual continuity was to come up with a family of structures that could be adapted to suit the varying skews, span arrangements and site conditions present at each bridge. The preliminary design was therefore undertaken on the basis of looking at groups of structures rather than individual bridges, so that a ‘best fit’ solution could be identified. The groups that were examined were as follows: • Structures 2, 6 and 9: These are the

overbridges at the interchanges, which would have similar spans and low skew;

• Structures 8 and 12: The high skew/curved overbridges carrying existing local roads over the mainline;

• Structures 1, 10 and 11: Three underbridges with medium skew and most likely to be single span solutions;

• Structures 4 and 5: The underbridges carrying the mainline over the railway and the directly adjacent (and busy) Glenealy Road;

• Structure 7: the Vartry River Bridge, carrying the mainline over the relative small but ‘flashy’ Vartry River;

• Structure 3: Cuckoo Lane Underbridge,

passing through a 18 high embankment as mentioned above;

• Structure 13: The Chapel River Underbridge, carrying the mainline over a steep hillside river, with the mainline on high embankment.

The following generic solutions were examined for the majority of the bridges: • Precast prestressed concrete composite

construction; • In-situ reinforced concrete construction; • In situ post-tensioned concrete construction; • Steel/concrete composite construction. Various span arrangements were also considered, including for example, 4 span overbridges. Each option was considered under the headings of general suitability, construction cost, maintenance costs, safety, constructability, foundation requirements and aesthetics. During this process, one option was developed with Murray O’Laoire which stood out over all the others. Taking the natural environment as inspiration, a concept of a set of bridges, utilising the mouldability of concrete to mimic the organic shapes found in nature, emerged. The core concept was to provide structures that would appear to grow from their supports in the manner of a flower with the curved petals supporting the deck. As a deliberate contrast, wedge shaped abutments to each bridge would act as visual counterpoints to the organic deck form, with solid wingwalls to top of parapet level to emphasise the transition from road to bridge for both traffic on the bridge and below. This solution could be used for both overbridges and underbridges and would allow any span combination or skew to be accommodated (see figures 2 to 5).

Figure 2: 2 Span Overbridge



Figure 3: Single Span Underbridge

Figure 4: 3 span underbridge

Figure 5: 4 span underbridge

As a team, we knew these looked great, and that the concept could be extended to cover 9 of the 13 bridges. There were two questions however: 1. How to make them stand up; 2. What would be the cost of all that curved

formwork? The first question was answered relatively straightforwardly: an in-situ post-tensioned concrete box girder with central spine and span/depth ratio of approximately 20 to 22 would work structurally. The typical cross section proposed for overbridges is shown in Figures 6. The formwork cost question was more complex. For an overbridge, formwork normally makes up about 10% of the construction cost per metre of deck. If the proposed shape was for a ‘once off’ structure,

Figure 6: Typical Overbridge Cross-Section

the cost of the curved and warped formwork could add as much as 30-40% to the cost over standard ‘flat’ formwork. It was clear that the only way it could make economic sense would be to maximise the reusability of the formwork. A two-pronged exercise was therefore undertaken; Firstly, the road alignments were rationalised including measures such as ‘squaring up’ the overbridges at the interchanges, and providing constant curvature/ super-elevation on bridge decks. This involved some redesign of the interchanges and minor roads. The second task was to standardise the bridge cross-sections and spans wherever possible so that the same shutter could be reused multiple times. This latter exercise reduced the number of different curved edge/soffit profiles to 3, and the number of different structural depths to 4 (1300 mm for all underbridges, and 1400 mm, 1600 mm and 1800 mm for the overbridges). Using this approach, the projected cost of the bridges at preliminary design stage ranged from €1075/m2 to €1170/m2 for the overbridges and €1100/m2 to €1430/m2 for underbridges (all figures based on 1999 construction costs, including 15% for contract preliminaries and excluding VAT). Although somewhat (10 to 15 %) more expensive than the standard precast or in-situ concrete solutions examined, these costs were considered reasonable given the visual quality of the design. The final element of the preliminary design of the family of bridges was to prepare a 1:100 scale model of the ‘standard’ overbridge to make sure that the concept worked visually in 3 dimensions. The model, with added background detail, is shown in Figures 7 and 8.



Figure 7: 1:100 scale model

Figure 8: 1:100 scale model

The ‘organic’ concept was therefore recommended to Wicklow County Council and the NRA for the 9 bridges concerned, and was subsequently approved for all 9 bridges. The remaining four bridges did not fit into the family of ‘organic’ bridges due to site constraints, and more conventional solutions were adopted: • The height of road embankment at Structure

3 dictated that a buried structure would be the best solution, hence a precast arch was recommended;

• Construction over the railway would be best achieved using prefabricated components and a single span precast beam deck was chosen. For consistency, this option was also recommended for the adjacent Glenealy Road Underbridge;

• For the 113 m long Chapel River Bridge, with the river flowing down the side of a steep hill, and in rock, it was decided to use a buried in-situ portal frame structure. The use of in-situ concrete, rather than precast, was chosen to allow maximum flexibility on site to make modifications to suit the site conditions.

2.2 Detailed Design The structural analysis for detailed design of the bridges was carried out using the ENCAD suite of programmes, LUSAS for finite element modelling and POSTTEN for the design of post-tensioning at SLS and ULS. The analysis work was split into three main parts:

• A 2D grillage for the longitudinal design of each bridge, with primary longitudinal ‘spine’ beams at the locations of the webs of the box girder decks (see figure 9);

• A 3D frame analysis for transverse design to model the loads in the inclined bottom flange of the box girder/top slab (see figure 10);

• A 3D solid finite element model to check the distribution of applied loads, and to check for any shear lag effects that might be present (see figure 11).

Figure 9: 2D Grillage Model for Longitudinal Design

Figure 10: 3D Space Frame Model for Transverse Design

Figure 11: 3D FEA Results

In general, the longitudinal post-tensioning of the



deck was placed in the central webs following a typical parabolic profile in elevation with low point at the location of the maximum sag moment and high point over intermediate supports. Additional ‘axial’ prestress was used on the overbridges by placing additional straight ducts in other areas of the cross section. 2.2.1 Substructures and Foundations The ground conditions varied throughout the site from rock at Structures 2, 4, 5, 10 and 12 to very soft ground at Structures 6 and 7. The general principle adopted in design was to use driven precast concrete piles wherever a satisfactory bearing stratum was not available reasonably close to maximum underside of foundation level, and then to keep the level of the pilecap as high as possible to minimise its size. The final design placed 29 out of 49 individual substructures on piles, and the remaining 20 on spread foundations. 2.2.2 Specification Class 50/20 concrete was generally specified for all the in-situ structural concrete in the bridge decks and substructures. For long-term durability, and to reduce initial thermal problems, the specification for the bridges included 50% cement replacement with GGBS. In addition it was specified that the exposed concrete surfaces be impregnated and coated in accordance with Cl.1709 of the NRA Specification for Roadworks. As regards the formwork, the choice of formwork type to achieve the required F3 curved profiles was left to the contractor, with a requirement to construct a number of trial panels for approval by the Engineer prior to commencement of construction.

Figure 13: Column head formwork

2.2.3 Contractor Design Structures Based on past experience, where it is considered that a proprietary system is likely to be the optimum solution for a particular structure, it is highly likely that the contractor will propose either an alternative supplier or alternative form of structure once appointed. In recognition of this, rather than designing and measuring every element traditionally, the Contract made a number of the structures ‘Contractor Designed’, including Structure 3 (Cuckoo Lane Underbridge – a precast concrete arch), the three major retaining walls (likely to be reinforced earth), the 5 cattle underpasses and 5 of the major culverts. This placed responsibility for the selection of the most appropriate product with the contractor, who would design it for checking by the Engineer. Once approved, it would be adopted as the Engineer’s design. 2.3 Construction 2.3.1 Formwork The unique soffit profiles for 9 of the 13 bridges were achieved using plywood formwork, bent to shape on a series of ribs used as templates as shown in Figure 12. Bespoke birch shutters were manufactured by Doka for the column heads (see Figure 13). The tapered bridge piers were formed using steel shutters. Other formed finishes were achieved using T&G plywood shutters.

Figure 12: Typical curved formwork.



Figure 14: Soffit before impregnation and coating

2.3.2 Constraints Construction of many of the bridges and other structures had significant site constraints:

• As the N11 scheme is partly on the line of

the old N11, there were several areas where the construction of structures had to take place in close proximity to live traffic. Figure 15 shows temporary support to the existing N11 carriageway at Structure 1.

• The erection of precast elements, including beams and parapets, for the railway bridge took place during railway possessions (see Figure 22).

• A temporary bridge crossing of the River Vartry was used to facilitate construction of Structure 7 and movement through the site.

Figure 15: Construction adjacent to live N11 traffic at Structure 1

2.3.3 Chapel River Bridge One of the more difficult structures turned out to be Structure 13, the Chapel River Bridge, but for unexpected reasons.

The details of the treatment of the watercourse had been agreed with the Eastern Regional Fisheries Board during the detailed design stage. Once construction started, the ERFB placed increased importance on the salmonid status of the river, resulting in more stringent requirements on construction. The end result was the construction of an internal fishpass as shown in Figure 16, as opposed to the original ‘as excavated’ treatment.

Figure 16: Fish pass at Chapel River Bridge

2.3.4 Contractor Designed Structures In practice, the contractual approach of making structures that were likely to become proprietary solutions worked well, although, as would be expected, there was some discussion on the design methods and details for some of the structures. Interestingly, the 3 contractor designed retaining walls were constructed as reinforced slopes, with a face angle of 70 degrees. These were constructed very efficiently using stainless steel mesh reinforcement. The only area of contention was the inclusion of measures for dealing with existing soft ground at Structure 3, where the Contractor eventually chose a ground replacement solution.



Figure 17: Structure 3 (Precast Arch) Cuckoo Lane

2.4 Bridge Costs The preliminary estimates and tender costs excluding VAT for the bridges on the scheme are shown in the following table (Note that the ‘final’ figures are included in the buyout, which did not itemise the structures costs, hence exact figures are not available). Phase Preliminary

1999 Tender

2001 Total €13.484m €14.112m

(+2.2% p.a.)

Table 1: Bridge Costs

Construction Complete September 2004 Photographs of completed structures are shown in Figures 18 to 23.

Figure 18: Structure 2 (Typical Overbridge) Ballynabarny

Figure 19: Structure 12 Timmore Lane

Figure 20: Typical Pier

Figure 21: Typical Underbridge



Figure 22: Structure 4 Railway Bridge (precast U beams and precast parapets)

Figure 23: Structure 8 Mill Road

3.0 Earthworks Substantial earthworks operations have been undertaken in this project, primarily concentrated in the areas of cut and fill and at the structural features such as bridges and off ramps. There are six main areas of cut along the route. All but one required rock excavation. 3.1 Preliminary Site Investigation A geophysical investigation was undertaken in 1998 as part of the geological report for the EIS. 2D resistivity and seismic refraction techniques were employed in a geophysical walkover survey of the route. 2D resistivity provided interpretative information on overburden characteristics and depth to bedrock. Seismic surveys provided interpretative information on the quality of the bedrock. A select number of overburden and rock boreholes were also undertaken. 3.2 Main Site Investigation The main site investigation for the Newtownmountkennedy to Ballynabarny Road Improvement Scheme, as specified by Arup Consulting Engineers was undertaken by IGSL in accordance with the British Standard BS5930: 1999 Code of Practice for Site Investigations. The site investigation factual report was used as the basis for

the design of the scheme and subsequently provided as part of the tender documentation.

Rotary Core holes were drilled in the winter months of November 1999 to March 2000. Due to the poor weather during these months, ground conditions were significantly wet. Some landowners imposed land access restrictions, and the location of some boreholes had to be repositioned, with occasional positions being abandoned. Consequentially, a number of areas yielded sparse information about rock quality. In general, the route alignment investigation had a reasonable frequency of rock core locations. However, the significant intrusions of hard, igneous rock encountered during construction were not intersected by any of the rotary core holes undertaken in the site investigation. Rock cores were logged in accordance with BS5930: 1999 by a geologist. A timeframe of two months elapsed before rock cores were logged. During this period the rock cores would have experienced a stress relief, stored in unconfined core boxes. While this conventional but delayed rock core recovery and storage may be expected to create minor fracturing, evidence from bulk excavations during construction has clearly shown this phenomenon of rock fracturing due to stress release to be extreme on this site, particularly in Cut 5 at Inchinappa Hill. The effective stress release combined with movement during transportation appears to have led to a breakdown of the rock core. Consequently, the rock in the core appeared to be more fractured than that which was encountered on site. 3.3 Rock Excavation and Reuse At an early stage in the earthworks programme, it became apparent that the Contractor was having difficulty with excavation of some of the rock cuttings using rippers and breakers. Production levels were seen to decrease and larger and greater numbers of plant were brought in to maintain the planned production output. As cuts were deepened, the rock mass was seen in many instances to be more difficult to excavate than had been anticipated by the Contractor. Under Clause 12 (1) of the IEI Conditions of Contract, “Adverse Physical Conditions and Artificial Obstructions”, the Contractor can claim to recover costs, if unforeseen physical conditions have been encountered. The nature and extent of fresh chrystalline igneous dolerite, its manner of intrusion, massive nature and high strength combined with the local metamorphic alteration of the surrounding rock by the igneous intrusions, were the overriding



factors that resulted in Clause 12 terms of contract being applied.

When the first Clause 12 claim was submitted by the Contractor, a joint approach was taken by Arup and the Contractor’s representative, to identify the quantity of rock which might fall into the category of ‘unforeseen ground conditions’. This process involved the compilation of data sets from exposed rock surfaces throughout the excavation of each cutting. Additionally, random rock samples were collected, classified and tested for rock strength. Comparisons were then made between the new information obtained and that of the original site investigation information provided at the time of tender.

Data collected was also cross-referenced with horsepower hours expended over the course of the excavation. The difference between what the Contractor might reasonably have been expected to foresee and actual ground conditions encountered was then derived. The grounds for the Clause 12 claims and the method adopted for their quantification were independently verified. The Clause 12 claims were carried into the negotiations undertaken to reach a financial settlement for the Contract as a whole. There were beneficial aspects to the occurrence of harder rock, in that an additional volume of granular fill material was recovered from rock excavations within the site. Approximately 1.35 million cubic metres of broken rock material was recovered from site as opposed to the one million cubic metres predicted from the results of the original site investigation. This additional rock saved costs on importing fill from local quarries and also reduced potential traffic volumes on county roads. An estimated saving of approximately 22,700 lorry-loads, equivalent to 45,400 lorry roads journeys was achieved.

An equivalent volume of natural resource was also preserved, as this granular fill was not required from any source outside the site.

If the identification of the presence of harder rock had been established at the time of tender, in all likelihood the cost of its excavation would have been reflected in the tender price. 4.0 Planning the Project – The Contractor’s

Approach While the customary pre-tender planning exercises were carried out during the tender period of May to July 2001, planning the project in earnest did not commence until September 2001 when it became apparent that the Morris Sisk Consortium were likely to be the successful tenderer.

A detailed draft programme and earthworks mass haul study was prepared. An intensive study to identify prospective borrow pits was carried out, leading to the selection of five possible sites, which, following more detailed ground investigation was reduced to four preferred sites. Earlier enquiries for earthworks resources were followed up and staff from the two parent companies were earmarked for the project as recruitment of other staff commenced. As a result when the Contractor’s tender was formally accepted in mid-December 2001, agreements in principle were already in place with a major earthworks sub-contractor and with three of the four preferred borrow pit owners. Following formal acceptance of his tender the Contractor moved to finalise agreements with sub-contractors and landowners and initiated the formal Planning and Waste Permitting processes for the borrow pits.

The process of finalising an overall plan and works programme also commenced at this stage. It was considered that optimisation of efficiency in earthworks and the necessity of using expensive plant efficiently should be the dominant programme determinants and were carefully considered and planned. In general terms this was done by looking at the ‘Employers Earthworks Schedule’ provided as part of the tender documents together with the potential borrow pit scenarios, identifying the shortest hauls and developing an optimum earthworks movement schedule. This schedule was then reviewed and refined in the context of the draft programme, the various constraints and restraints on the work, and the available resources, and was developed into an earthworks programme. After some further adjustment to ensure compatibility with the developing programme, the earthworks programme was incorporated into the Contractors overall programme (the Clause 14 Programme).

In parallel with the development of the earthworks programme the various other works were also planned. In particular, the programming of the structures was finalised by aiming to achieve the most efficient use of resources within the overall programme requirements. Five similar overbridges with similar decks were sequenced to facilitate reuse of a pre-manufactured deck formwork system. Four similar underbridges were also planned to facilitate maximum reuse of formwork with other more stand-



alone structures being slotted in to suit an overall programme. In this way the sub-programmes for the various works activities were consolidated into the overall programme and plan for the works, which was finalised in mid-February 2002 just as works were commencing on site.

4.1 Progress Phase 1 (Feb 2002 to Jan 2003) Works commenced on site in mid-February 2002 with site clearance and fencing. The early season start was dictated by the requirement to get the bulk of the site clearance done before March to satisfy the requirements of the Wildlife Acts. Work commenced on stripping of topsoil in mid-March, on structures at the beginning of April and on bulk earthworks by mid-April.

However, by the end of April some serious impediments to achieving the planned progress were becoming apparent and were having an increasingly disruptive effect on the progress of the works. The contract provided for the supervision of topsoil stripping by the Employer’s archaeologist but because of the necessary follow on archaeological investigations of potential discoveries and sites, a significant number of areas both large and small was effectively fenced off to all contractor access.

Difficulties were also encountered in obtaining possession of a number of key parts of the site. Some of these severed access along the site completely and, taken together with the archaeological sites severely disrupted the planned movements and programming of earthworks.

One of the key objectives of the earthworks programme had been to substantially complete the bulk excavation of soft material in the first earthworks season and follow through and substantially complete the rock excavation in the following Winter and Spring. This objective was not achieved leading to further delays in accessing some of the rock heads. It also became apparent in the Autumn of 2002 in the rock areas available that the rock was proving significantly more difficult to excavate than anticipated. This resulted in much reduced outputs, a requirement for additional and larger plant and a greater reliance on blasting of rock.

On the Structures side progress was reasonable throughout the first year but a later than expected start, combined with a slower than anticipated learning curve assembling the complicated deck formwork meant that by late 2002 the structures as a whole were about two and a half months behind. A decision was made at this stage to fabricate a second set of formwork for the overbridge decks allowing this delay to be recovered fully over the following

months. Additionally the disruption of the earthworks operation required a re-sequencing of the structures.

Fig 24: Archaeology prevents progress on bulk earthworks

Fig 25: Typical rock excavation on site

4.2 Progress Phase 2 (February 2003 to December 2003)

By the beginning of 2003, the works were generally five months behind programme with some activities further behind. While the programme was revised and updated at various stages throughout 2002, the basic logic underlying the programme had been so undermined by the difficulties encountered that the programme’s usefulness as a management tool was highly questionable. It was also at this stage that the extent of the difficulties being encountered on site was becoming fully apparent.

In consequence at this point a new plan and programme to completion was prepared from first principles so as to take account of the revised circumstances and the actual progress position on site. This new programme was ambitious in its approach and resourcing, and envisaged completion in September 2004, about two months later than the original programme.

While the contractor struggled initially to meet some of the deliberately ambitious targets set in the new programme to completion, progress was generally



back in line with the new programme within three months and notwithstanding some modifications to the detail of the programme, progress remained on line until completion in September 2004.

It should be acknowledged that a number of influencing factors, which had hindered progress in 2002, assisted progress in 2003. The extremely wet and inclement weather between May 2002 and January 2003 gave way to an almost unprecedented dry spell which stretched from February 2003 to June 2004. As a result, topsoiling operations, which had been scheduled to be suspended during the 2003/2004 winter, continued throughout the winter and the main surfacing operation, which commenced in June 2003 continued without interruption until it was completed shortly before opening in September 2004. Possession of the last significant section of the site was received from the Employer in early 2003. The earthworks sub-contractor had by February 2003 assembled sufficient additional resources to deal with the rock difficulties. In parallel with all this there was significant progress being made in the resolution of the contract and commercial issues associated with the various difficulties that had been encountered. All of these factors contributed to an increasing momentum on the project which was not diminished by other difficulties which arose and which continued right up until completion.

Fig 26: Reuse of rock excavated in the works

Fig 27: Assembling curved formwork

4.3 Progress Phase 3 (Jan 2004 to Sept 2004) The primary focus of the programme for 2004 was the removal of the remaining plug areas (areas where works were not possible due to traffic routes or other constraints). Although a number of these were eliminated in 2003, there were still seven significant plugs on the new N11 route at the beginning of 2004, one at each tie-in and five where N11 traffic crossed the new route at various points. These plugs were eliminated by diversion of N11 traffic onto completed sections of the new road on a staged basis.

A notable aspect of the management of the project during 2004 was the particular focus given to finishes and snagging. A separate plan was put into place in January 2004 to complete the finishes and snagging in a sequenced and organised manner in tandem with the various traffic diversions leading to a staged effective sign-off of large sections of the works.

While the plan gave rise to some tensions on site, it has proved to be a great success. When the project was formally opened on the 27th September 2004 all the main areas of the works were finished and snagged out. All post completion works will be finished within a month of the opening allowing a full demobilisation of resources at that stage. This is not the norm for projects of this scale and no remobilisation is envisaged until any defects are addressed near the end of the Maintenance Period.



Fig 28: Ballynabarny Interchange Fig 29: Mill Road Overbridge

Fig 30: Earthworks at Interchange Fig 31: Farm Accommodation works at Ballynabarny

5.0 Archaeology 5.1 Archaeological Findings Prior to construction of the Newtownmountkennedy to Ballynabarny Road Improvement Scheme Project, County Wicklow already had a known heritage rich in archaeological monuments and sites ranging from the prehistoric to the post-medieval. However, as a result of construction of the scheme, records were provided of an astonishing array of over 50 additional sites of archaeological interest. Many were large hilltop ritual enclosures with cremations dating from the late Neolithic to the Early Bronze Age. Others ranged from typical Bronze Age sites such as fulachta fiadh to possible settlements of the early Christian to late medieval period: It is clear that a wealth of new archaeological evidence arose out of the scheme. Whilst the significance of the findings is still being assessed, the overall conclusion which must be reached is that there once was a much higher density of prehistoric settlement throughout County Wicklow than was hitherto believed. 5.2 Impact of Archaeology on Construction Archaeology encountered on the scheme had a major impact on cost and programme.

The strategy employed at the outset was to pre-empt as far as was practical, disruption to the earthworks that might occur during stripping of topsoil under the Main Contract.

To this end, a “Pre-Contract” phase of archaeological investigation was initiated. Areas of the site were selected for this treatment on the following basis:-

a) those which were known to be accessible from

landowners’ points of view,

b) those presenting visible topographical or other features adjudged likely to indicate the presence of archaeological sites, and

c) those thought likely to be prioritised in a roadworks contractor’s earthworks programme.

At the earliest possible juncture, a pre-award liaison was set up with the likely successful tenderer in order to establish priorities in his programme.

As it turned out, the pre-contract archaeological phase lasted over a year, and as such, overlapped the Main Contract by about 6 months. Despite this, some 25% of the total number of archaeological sites discovered on the project was “resolved” archaeologically before they could interfere with the



Main Contract.

On a sequential number basis, the project archaeologist identified some 85 active sites grouped as follows:

Table 2

The effects of archaeological activities on the Contractor’s construction operations included:

a) lack of access to areas of the site on programmed start dates;

b) necessity to abandon or circumvent spontaneously sterilised parts of the site;

c) unplanned demobilisations from and remobilisations to sterilised areas of the site;

d) interference with haul routes and cut/fill balances;

e) double handling of earthworks materials;

f) multiple knock-on effects.

Given the variability in type and severity of causes and effects it is impractical to assess and calculate the actual cost of disruption attributable to each archaeological site.

With a view to assessing the overall cost impact on the Contract, however, using their records, experience and knowledge of what actually occurred on site, Arup carried out an exercise involving categorisation of sites using criteria such as size, spontaneity of occurrence, duration of interference and severity of impact.

For each category of site, additional resources that it would have been reasonable to deploy in response to disruption were estimated. Costing norms were then used to arrive at the cumulative cost of disruption as a whole.

Derived in this way the total cost of interference by archaeology with the earthworks activities was of the order of €1.5 m.

Adding this to the €4.5m projected cost of the Project Archaeologists services gives a total cost of archaeology associated with the project of the order of €6 m. 6.0 Supervision and Working Relationships

At the outset on the Newtownmountkennedy to Ballynabarny scheme, some brainstorming by the Contractor led to his proposal to accommodate both his own staff and the Resident Engineer’s staff in a disused former hotel premises.

Only after considerable deliberation did the Engineer decide to approve of his staff being accommodated in such close proximity to the Contractor’s staff. However, in the early months of the project it was clear that the good relations developing between the parties were being enhanced in no small way by them having to share facilities and rub shoulders with one another on a daily basis.

A good working relationship was very soon consolidated, and one typical manifestation of this was the successful combining of the Engineer’s and the Contractor’s resources in a shared laboratory.

The laboratory was run jointly by a representative from each party. To their credit, a code of procedure developed by these representatives, ensured that the possibility of a “theirs and ours” syndrome never arose.

The Contractor established the services of offsite independent accredited laboratories where such was required under the Contract. However, independent testing that did not require specific accreditation was carried out in the joint site laboratory.

This was not the scenario envisaged in the Contract, but distinct advantages for both parties were realised:

No. of Archaeological Sites

Phase Total Identified

Minimal Interference

Significant Disruption

Pre-contract

Contract (Spontaneous)

22

63

10

10

12

53

Totals 85 20 65

1. The expense of duplicating laboratory personnel, facilities, equipment and vehicles was spared.

2. Due to the magnitude of the earthworks operations in particular, the testing regimes had to be extremely fast track. From the Resident Engineer’s perspective, because he had hands-on instant access to compliance testing procedures required under the Contract, he had much better control of the materials being used in the permanent works.

3. The potential for dispute between the Contractor and the R.E. over two different sets of results was eliminated, as all the testing was carried out or observed jointly.

4. Problems with materials that were out of specification could be highlighted, addressed and rectified expediently with singular focus.



For a time in the middle phase of the Contract, the harmony of the early days became somewhat frayed at the edges on account of differences of opinion arising over contractual issues. However, this turned out to be only a temporary wobble as, following successful negotiation of the buyout, the adversarial approach vanished and peace was restored.

In the following months, the Contractor sponsored a series of presentations for the Engineer’s and Contractor’s supervisory staffs. As part of these presentations, both parties joined in promoting their respective roles for the completion of the project as being complementary. The need for continued focus on joint measures necessary to assure quality of workmanship, and for early attention to the process of completing, snagging and formally handing over of work, were emphasised.

With these motivations in place, the parties joined forces to tackle the task of securing early completion of the project to the highest standards and within the newly established fixed price budgetary constraints.

8.0 Conclusion This is an example of a job where cooperation between a Contractor, the designer, the resident staff, the NRA and the Local Authority allowed a potentially protracted and dispute afflicted contract to be amicably brought to an early completion within an agreed final outturn cost, without any compromise on quality.

9.0 Acknowledgements

7.0 Accommodation Works To facilitate the scheme,144 hectares of land were compulsorily acquired from a total of 95 landowners at a cost expected to exceed €26 m.

In addition to this, some €4 m was billed under the Main Contract for accommodation works. In the final analysis, this amount is expected to exceed €5 m by a considerable amount.

With hindsight, the magnitude of the increase can be attributed to the following:-

• Interpretations by the designers of plan drawings and contracts drawn up by the Client for individual landowners appear to have been too literal, and failed to embrace wider associated engineering needs.

• Due to time and resource constraints, negotiations between Client and Landowner were incomplete when the Contract documents went to tender. In consequence, variations continued to arise well into the Contract period. A considerable percentage of these were seen to arise after much of the work was complete, when the landowner himself was in a position to appreciate fully exactly what he was getting on the ground and how it would affect his home or his livelihood.

The authors wish to thank Wicklow County Council and the NRA for permission to prepare this paper, and, in particular Tom Gorman, Marc Devereux and Tony Harte for their assistance in its preparation. Our thanks also go to our colleagues in Arup, Morris Sisk Consortium and Wicklow County Council without whose help the project could not have been delivered in such a successful and cost effective way.

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