Case Study - Cellweb TRP - Keats Way (Extended CS)

Location:

New Development off Keats Way

Rushden

Northamptonshire

NN10 6EE

Project Description:

Overcoming Significant changes in

levels within the RPA

Technical Requirements:

• 2.4m change in levels

• Curve Design

• Vegetated embankment face

Consultant:

JPP Consulting Civil and Structural

Engineers

Merchant:

Construction Lines

Contractor:

South Midlands Homes

Fleming Road Harrowbrook Industrial Estate

Hinckley LE10 3DU

Tel. 01455 617 139 [email protected]

www.geosyn.co.uk

Case Study

Cellweb® TRP

Overcoming significant changes in levels within the Root Protection Area

New Development off Keats Way, Rushden, Northampton

Introduction

Following their recommendation in Arboricultural Practice Note 12 and BS 5837 2005 and 2012, three dimensional cellular confinement systems have been widely used as a no dig solution in the construction of new hard surfaces within root protection areas (RPA’s). The use of an open structured granular infill material offers vertical and lateral water permeation and enables continued gaseous diffusion between the rooting environment and the atmosphere. More often than not, the system is installed on relatively level sites, and there is a perception that the system is unsuitable for anything other than level terrain. In this case study we will look at how Cellweb®TRP has been used to overcome significant changes in levels within the RPA, while maintaining a healthy environment for tree roots.

Geosynthetics Limited were approached by JPP Consulting Civil and Structural Engineers regarding a new residential development on land off Keats Way, Rushden Northamptonshire. The area of land to be developed could only be accessed from Keats Way and a new access road would need to be constructed. The only feasible route for the new road would pass through the RPA of a large Beech tree. The Beech was considered to be of high amenity value and was to be retained within the new development, which meant that a ‘no dig’ tree root protection system would need to be used for the construction of the access road. Figure 1 shows the proposed route of the new access road passing through the RPA of the Beech, as out lined by the red circle. The blue hatched panels across the width of the access road denote panels of Cellweb®TRP.

Keats Way, Northamptonshire

Figure 1: Sourced JPP Consulting

FFL58.450

FFL58.450m

FFL58.325m

FFL58.025m

FFL58.025m

FFL58.900m

FFL59.350m

FFL60.425m

FFL60.725m

FFL61.025m

47.571

59.900

Title

Project

Client

Status

Scale at A1 Drawn by Checked by Date

Project ref Drawing no. Revision

S. Midlands New Homes

Proposed Development

Off Keats Way

Rushden, Northamptonshire.

Plan Showing Extents of

Geosyn Cellweb System

1:100 JRY May 2014

PRELIMINARY P5710/PP E105

NOTES

GENERAL

Do not scale from this drawing.

All dimensions are in metres unless noted otherwise.

This drawing is to be used in conjunction with all relevant drawings,specifications, details and the Ground Investigation Report.

All highway works shall be constructed in accordance with NorthamptonshireCounty Councils 'Estate Road Construction' dated June 1999 and their'Design for Residential Roads' dated January 2000 together with the currentManual for Streets and Highway Works.

Geosynthetics Limited | Fleming Road | Harrowbrook Industrial Estate | Hinckley | LE10 3DU Tel. 01455 617 139 | [email protected] | www.geosyn.co.uk

Case Study

Cellweb® TRPKeats Way, Northamptonshire

CHAINAGE

EXISTING GROUND LEVEL

ALIGNMENT LEVEL

VERTICAL ALIGNMENT

HORIZONTAL ALIGNMENT

61.0

00

60.7

07

0.00

0

60.4

17

60.3

10

11.3

17

59.1

62

58.0

48

39.2

80

R= 78.400

57.8

79

55.5

19

R= 11.600

58.0

67

58.7

31

60.7

36

77.1

08

R= 45.000

51.4

14

1.98

0

CHAINAGE

EXISTING GROUND LEVEL

ALIGNMENT LEVEL

VERTICAL ALIGNMENT

HORIZONTAL ALIGNMENT

58.0

410.

000

58.0

25

2.06

6

58.1

09

11.3

76

R= 22.375

15.5

87

61.0

44

G= -1.914%1: -52.2

5.00

060

.986

10.0

0060

.890

15.0

0060

.795

20.0

0060

.699

25.0

0060

.603

29.2

1360

.523

L= 10.000KF= -6.05939

30.0

0060

.507

35.0

0060

.384

39.2

1360

.249

58.8

98

G= -3.565%1: -28.1

40.0

0060

.221

45.0

0060

.042

50.0

0059

.864

55.0

0059

.686

60.0

0059

.508

65.0

0059

.330

70.0

0059

.151

75.0

0058

.973

60.9

2660

.926

60.8

3060

.830

60.7

3560

.735

60.6

3960

.639

60.5

4360

.543

60.4

4760

.447

60.3

2460

.324

60.1

6160

.161

59.9

8259

.982

59.8

0459

.804

59.6

2659

.626

59.4

4859

.448

59.2

7059

.270

59.0

9159

.091

58.9

1358

.913

58.8

3858

.838

LEFT HAND CHANNEL

RIGHT HAND CHANNEL

2.40

059

.754

60.2

94

G= 4.095%1: 24.4

5.00

059

.860

10.0

0060

.065

15.0

0060

.270

59.8

205.

485

60.2

34

59.9

58

60.2

34

59.9

588.

854

60.0

0560

.005

60.2

1060

.210

60.2

3460

.234

LEFT HAND CHANNEL

RIGHT HAND CHANNEL

DATUM 55.000

60.000

Proposed Long Section Through Road 1(Scale 1:200 Horizontal, 1:50 Vertical)

Road

Lev

el (K

eats

Way

)

Cent

re L

ine

of R

oad

2

Proposed centreline level

Proposed channel level

Existing ground level

Cent

re L

ine

of R

oad

1

DATUM 55.000

60.000

Existing ground level

Proposed centreline level

Proposed channel level

Proposed Long Section Through Road 2(Scale 1:200 Horizontal, 1:50 Vertical)

Hatching indicate approximate extent of retaining wall.

Half batter kerb type HB2

1:40 camber

4.8m wide carriageway1.0m Service Strip

1:33

1.8m footway

1:33


1:40 camber

Precast concrete footwayedging type EF Precast concrete

footway edging type EF

Typical Cross Section Through Road 1(Scale 1:50)


1:40 camber

4.8m wide carriageway1.0m Service Strip

1:33


1:40 camber

Precast concrete footwayedging type EF

Typical Cross Section Through Road 2(Scale 1:50)

1.0m Service Strip

1:33

Precast concrete footwayedging type EF

Title

Project

Client

Status

Scale at A1 Drawn by Checked by Date

Project ref Drawing no. Revision

S. Midlands Developments

Proposed DevelopmentOff Keats WayRushden, Northamptonshire

Proposed Long Sections

As Stated DL PAB October 2011

PRELIMINARY P5710/PP E112

NOTES

GENERAL

Do not scale from this drawing.

All dimensions are in metres unless noted otherwise.

This drawing is to be used in conjunction with all relevant drawings, specifications, details and theGround Investigation Report.

All highway works shall be constructed in accordance with Northamptonshire County Councils'Estate Road Construction' dated June 1999 and their 'Design for Residential Roads' dated January2000 together with the current Manual for Streets and Highway Works.

The site posed a second challenge in the form of its terrain. Over the length of the access road there was a fall in levels of 2.4m from the southern end of the road at Keats Way to the Northern end of the road in the new development. Figure 2 below shows a longitudinal section showing how the existing ground level changes along the route of the proposed new access road. The hatched area represents the area where the ground level needed to be built up inside the RPA.

Any increase in levels within the RPA should be carried out and constructed to ensure continued water permeation and gaseous exchange to and from the rooting environment and the atmosphere. If this is not maintained and anaerobic conditions are created, it can result in root death and ultimately bring about the demise of the tree. To overcome this change in levels it required a build-up of 2.4m above the existing ground level at the most southern end of the RPA, reducing to 1.2m above the existing ground at the most northern point.

The Engineering department at Geosynthetics Limited calculated a site specific technical recommendation and proposed the solution that can be seen in figure 3. The solution shows how layers of 200mm depth Cellweb®TRP can be stacked on top of each other to increase levels. The system can then be terraced to create a gradual reduction in levels as the route progresses north towards the new development. This solution was adopted and a full design was carried out by JPP Consulting Civil and Structural Engineers.

Figure 2: Changes in existing ground level

Figure 3: Stacked 200mm depth Cellweb® TRP


Case Study


Photo 1, shows the first layer of Cellweb®TRP being installed, with the retained Beech tree on the left. Minimal excavation was carried out on the far southern extremity of the RPA, at the entrance from Keats Way. This was carried out to create a flat surface to which 2.4m of Cellweb®TRP would need to abut. The Cellweb®TRP system is pegged out over the top of one layer of Treetex™ Geotextile. This acts as a separation layer, preventing the infill aggregate from migrating into the subgrade below. This also acts as a pollution control measure in accordance with BS 5837 2012.

Photo 2, shows the progression of the installation and the layering of the Cellweb®TRP. To the right in the photo and next to the tree we can see the beginnings of the formation of a Cellweb®TRP embankment. This batter is designed to have a gradient of one in three and is infilled with the same 4-20mm clean angular stone used to infill the rest of the system. The end cells of each layer of Cellweb®TRP are left empty and are later filled with topsoil and are planted to create a vegetated embankment.

Photo 1: First Layer of Cellweb®TRP being installed

Photo 2: Layering of the Cellweb®TRP


Case Study


ConclusionIt can be seen from this case study that with thoughtful design Cellweb®TRP can be utilised on far more challenging sites than previously thought. This is particularly poignant at a time where we see increasing demand for development land, which places ever increasing pressure on our national tree stock. The benefits of trees are becoming increasingly recognised and it is important that we utilise engineered solutions to enable us to retain healthy trees as part of future developments.

The Beech tree in this case study now forms part of an ongoing programme to assess the health and vitality of trees which are subject to the construction of Cellweb®TRP systems. More information on this programme is available by contacting Geosynthetics Tree Root Protection team on 01455 617139.

Photos three and four below, show the completed access road and development eighteen months later. In photo three it can be seen that the Cellweb®TRP section of the new access road is surfaced using permeable blocks, allowing continued water permeation and gaseous exchange. The remaining road outside of the RPA is constructed using a conventional subbase with an asphalt surface. In photo four we can see the completed batter which passes around the main stem of the retained Beech, allowing enough space for the future incremental growth of the buttress roots. The end cells of each layer of Cellweb®TRP have been infilled with topsoil and are now planted to create an attractive vegetated bank.

Photo 3: Finished development Photo 4: Close up of the finished development

Case Study - Cellweb TRP - Keats Way (Extended CS)

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