Appendix 16.3: WSP Ltd, June 2014. A45 Daventry Link Road, Ground Investigation Report · 2017-02-13 · A45 Daventry Link Road Ground Investigation Report 39880 June 2014 1 INTRODUCTION

Appendix 16.3: WSP Ltd, June 2014. A45 Daventry Link Road, Ground Investigation Report

A45 Daventry Link Road

Ground Investigation Report

Northamptonshire County Council 00039880

June 2014

QUALITY MANAGEMENT

Project Title: A45 Daventry Link Road

Report Title: Ground Investigation Report

Issue/revision Issue 1

Remarks Final

Date June 2014

Prepared by J Dyke

Signature

Checked by M Neden

Signature

Authorised by R Grainger

Signature

Project number 00039880

Document Ref. 00039880/10102

This report is addressed to and may be relied upon by the following parties: MGWSP Northamptonshire County Council Riverside House John Dryden House

Riverside Way Industrial Estate 8-10 The Lakes

Northampton Northampton

NN1 5NX NN4 7YD

CONTENTS



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1 INTRODUCTION 1

2 EXISTING INFORMATION 3

3 FIELD STUDIES 6

4 GROUND SUMMARY 9

5 EARTHWORKS AND STRUCTURES 11

6 MATERIAL PROPERTIES 15

7 GEOTECHNICAL RISK REGISTER 32

8 REFERENCES 33

APPENDICES

Appendix A Drawings and Figures Appendix B Geotechnics Ltd. Factual Report Appendix C Historical Site Investigation Data Appendix D Alignment Option 6 Long Sections Appendix E Risk Register Notes on Limitations

EXECUTIVE SUMMARY


Ground Investigation Report i

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This report forms a record of geotechnical and geo-environmental works undertaken to investigate the ground and groundwater conditions underlying the preferred alignment – Route Option 6 – of the proposed A45 Daventry Link Road.

Route Option 6 is approximately 6.1km in length and designed to accommodate proposed development by forming a bypass around the villages of Flore and Weedon; this is to relieve congestion experienced on the current A45 where it passes through the two villages.

The alignment spurs from the existing A45 alignment to the northwest of Weedon, just to the south of Globe Farm. Descending in a north-easterly direction, the alignment crosses the West Coast Main Line, Grand Union Canal, A5 (Watling Street) and Wilton Brook before ascending towards Hobhill Spinney. As the route traverses the upper slopes of Hobhill it turns to the southeast, intersecting Brockhall and Brington Road, north of Flore. The route then runs parallel to the M1 crossing Hollandstone Brook and a farm access track before joining the current A45 alignment just west of Junction 16 of the M1. The route comprises both cutting and embankment earthworks and a total of nine bridge structures.

Ground conditions have been appraised based on published sources as well as recent and historical site investigation data. The geology underlying the route comprises Granular and Cohesive Glacial Till, Upper Lias deposits, Marlstone Rock Beds and Middle Lias deposits with localised accumulations of Alluvium and areas of Made Ground.

To aid detailed design the route has been divided into eleven earthworks sections and nine structures. A series of geological sections of the route are presented.

Material properties for use in the Geotechnical Design Report have been determined from in-situ testing, laboratory testing and published sources.


Ground Investigation Report 1

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1 INTRODUCTION

1.1 SCOPE AND OBJECTIVES OF THE REPORT

This report forms a record of geotechnical and geo-environmental works undertaken to investigate the ground and groundwater conditions underlying the preferred alignment – Route Option 6 – of the proposed A45 Daventry Link Road. Plan and section information of the preferred route have been presented in Appendix A (see Drawing S397/036).

The scope of the works was as follows:

Intrusive ground investigation;

Post investigation monitoring;

Laboratory analysis; and,

Reporting.

The objectives of the site investigation were to provide additional and updated information to that obtained during an earlier investigation undertaken in 1991 by Allied Exploration & Geotechnics Ltd. [1] and to provide new data on areas not previously investigated.

The objective of the report is to present site specific investigation data to facilitate earthworks design, pavement design and foundation design for structures.

This document forms a Ground Investigation Report and has been prepared in general accordance with guidance set out in British Standard EN 1997-2:2007 Eurocode 7 – Geotechnical Design [2]. As such the report provides a factual description of fieldworks and laboratory testing data, develops a conceptual ground model and presents characteristic material properties for use in detailed design.

1.2 DESCRIPTION OF THE PROJECT

Route Option 6 is approximately 6.1km in length and designed to accommodate proposed development by forming a bypass around the villages of Flore and Weedon; this is to relieve congestion experienced on the current A45 where it passes through the two villages. Plan and section drawings of the route have been presented as Drawing S397/036 in Appendix A.

The route spurs from the existing A45 alignment to the northwest of Weedon, just to the south of Globe Farm. Descending in a north-easterly direction, the alignment crosses the West Coast Main Line, Grand Union Canal, A5 (Watling Street) and Wilton Brook before ascending towards Hobhill Spinney. As the route traverses the upper slopes of Hobhill it turns to the southeast, intersecting Brockhall and Brington Road, north of Flore. The route then runs parallel to the M1 crossing Hollandstone Brook and a farm access track before joining the current A45 alignment just west of Junction 16 of the M1. The route comprises both cutting and embankment earthworks and a total of nine bridge structures.

1.3 PREVIOUS REPORTS

The following previous reports have been consulted in the preparation of this document:

‘A45(T) Weedon, Flore and Upper Heyford Bypass – Site Investigation Report’. Investigation undertaken by Allied Exploration Geotechnics. Report written by Michael D. Joyce Associates [1].

‘A45(T) Weedon, Flore and Upper Heyford Bypass – Desk Study Report’ written by Michael D. Joyce Associates [3].

This report should be read in conjunction with the Preliminary Sources Study Report [4] undertaken by WSPE in September 2013.



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1.4 LIMITATIONS

The Ground Investigation Report has been prepared as an assessment of the preferred route – Route Option 6 – and thus any discussion is limited to this alignment corridor only.

General notes on limitations have been presented at the back of this document.



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2 EXISTING INFORMATION

2.1 PREVIOUS INVESTIGATIONS

A previous site investigation was undertaken by Michael D Joyce Associates [1] along a similar alignment to that currently under consideration. Selected data from this investigation has been made available on the Highway Agency Geotechnical Data Management System (HAGDMS). The data available comprises 66 boreholes and 79 trial pits, as well as field and laboratory testing data. Given its relevance to the current route, this data has been referenced extensively throughout the project. Relevant excerpts from the available historical investigation data has been presented in Appendix C.

2.2 GEOGRAPHY AND TOPOGRAPHY

The villages of Flore and Weedon Bec are located within the Nene Valley near Junction 16 of the M1. The villages are approximately 1km apart with Flore to the east and Weedon to the west of the valley (see DWG/39880/01/01 in Appendix A).

The western end of the preferred route is at an elevation of approximately 120m AOD. The elevation immediately decreases as the route descends towards Wilton Brook, which lies at approximately 80m AOD. From here the route ascends Hobhill to a maximum elevation of approximately 104m AOD, before turning to the southeast and trending roughly parallel to the M1. This section of the route undulates but overall it descends towards a small, flat bottomed valley at approximately 77.5m AOD where it crosses Hollandstone Brook. From here the route ascends the eastern slope of the valley to around 89m AOD before crossing gently undulating ground and eventually re-joining the existing A45 alignment.

2.3 GEOLOGY

Based on published BGS geological mapping, the sequence of strata indicated to be present below the route is summarised in Table 2.1. An extract of the BGS Map Sheet 185 [5] overlain by the preferred route has been included as Figure 1 in Appendix A.

Table 2.1 – Anticipated Geological Sequence Geological Unit Material Type Indicative Thickness

Recent Alluvium Generally very soft organic rich deposits including peat, silt and clay. Superficial – variable

Granular Glacial Deposits Deposits of sand to cobble and boulder sized soils of varying density comprising various lithologies.

Superficial – variable

Cohesive Glacial Deposits Generally clays of varying strength with varying secondary fractions of sand to cobble and boulder size materials.

Superficial – variable

Upper Lias* (Whitby Mudstone Formation)

Interbedded calcareous stiff clay / silt grading to mudstone / siltstone with bands of sandstone and limestone.

47-60m

Marlstone Rock Formation Ferruginous limestone and ironstone interbedded with ferruginous sandstone and mudstone.

1-3m

Middle Lias* (Dyrham Formation)

Stiff and very stiff silt / clay grading to siltstone / mudstone with occasional tabular or nodular beds of limestone and units of sandstone.

16-30m

* It should be noted that the currently available 1:50,000 geological mapping for the area describes the underlying geology as comprising Middle and Upper Lias Deposits. However, the BGS has reclassified these deposits as the Dyrham and Whitby Formations respectively. To tie in with previous site investigation data, the now obsolete BGS names have been used.

This sequence is in general agreement with the findings of the original site investigation carried out by Michael D. Joyce Associates [1] in 1991.



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2.3.1 Ground Stability

The geology in the area is likely to have been affected by intense periglacial activity and weathering. It is possible that hill slopes greater than 8° may have undergone periglacial solifluction (see section 6.2.6 of PSSR [4]). Evidence of relict shear surfaces are indicated in the historical exploratory holes on the western slopes of Hobhill.

2.4 HYDROLOGY

2.4.1 General

Significant hydrological features encountered along the route include:

The Grand Union Canal encountered at chainage 700m;

Wilton Brook encountered at chainage 990m; and,

Hollandstone Brook encountered at chainage 4220m.

The published BGS 1:10,560 geological map SP66SW [6] indicates a number of natural springs on either side of Wilton Brook around the proposed crossing point.

2.4.2 Flood Risk

The Environment Agency website, accessed on 11 August 2013, indicates that there are two areas prone to flooding which affect the preferred route. These are summarised as follows:

Wilton Brook is considered to be at risk of flooding a considerable distance to the north and south of the area of intersection. The flood risk map indicates that the brook benefits from some flood defences in this area.

Hollandstone Brook is considered at risk of flooding around its intersection with the route. The tributary is culverted below the M1 in the same area.

The Environment Agency indicates a low ( 0.5% or 1 in 200 years) to moderate (1.3-0.5% or 1 in 75-200 years) likelihood of flooding for the above watercourses.

2.5 HYDROGEOLOGY

According to the Environment Agency, aquifer designation for the solid geology along the route is either Secondary Undifferentiated or Secondary A. Aquifer designation for the superficial deposits is Secondary A. Groundwater levels are likely to reflect topography and flow in relation to the nearby surface water courses of Wilton Brook and Hollandstone Brook.

2.6 HISTORICAL DEVELOPMENT

A review of historical ordnance survey mapping obtained via Landmark, indicates very little has changed over the last 130 years along the preferred route. Agriculture has dominated the land usage since the earliest available map (1884) to the present day. Historical development worth noting has been summarised in Table 2.2.

Table 2.2 – Summary of historical development along the proposed route Feature Location Details

Royal Ordnance depot 600m southeast of Ch0m

Present on historical OS maps between 1884 and 1958

Petrol filling station Ch52-93m Present on historical OS maps between 1971 and 1996

West Coast Main Line Ch585m Present on the earliest historical OS map (1884)

Grand Union Canal Ch700m Present on the earliest historical OS map (1884)



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Feature Location Details

Historical landfill - Dodmoor Farm / Dodford Landfill

Ch716-900m Licenced to take inert, household, commercial and industrial waste.

Possibly present at formation level under the northern embankment between Ch725m and Ch900m.

Historical landfill Ch5750-5900m Licenced to receive inert waste.

Expected to be outwith the alignment corridor.

A separate archaeological survey has been undertaken by Northamptonshire Archaeology to assess areas of archaeological significance along the preferred route. The findings of the survey are not detailed in this document and the reader is referred to the report by Northamptonshire Archaeology [7].

2.7 SERVICES AND STATUTORY BODIES

Composite service plans have been provided for the entire route and have been summarised based on their intersection with the route in Table 2.3.

Table 2.3 – Services along the route Approximate Chainage Details

30m Services within the carriageway / verge of the existing A45 alignment.

225m Overhead 11kV electricity cable

500m Water main from Dodford pumping station


585m Network Rail overhead line equipment


700m Telecommunication services within the tow path of the Grand Union Canal

915m Services within A5 carriageway / verge

1610-1640m Two water mains heading southwest towards Dodford pumping station.

1780m Oil pipeline


3100-4210m Water main crosses the alignment then runs parallel to the alignment.

4060m Overhead high voltage electricity cables supported on pylons

5415m Water main

5500-6100m Services within the carriageway / verge of the existing A45 alignment.

It should be noted that this summary is based on third party data that has been taken in good faith. However, WSP cannot accept liability for the content or accuracy of the plans provided.



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3 FIELD STUDIES

3.1 WALKOVER

A site walkover was undertaken by geotechnical engineers from WSP on 24 March 2013, the findings of which are discussed in the PSSR [4].

3.2 GROUND INVESTIGATION

3.2.1 Fieldwork

Fieldwork was undertaken by Geotechnics Limited under the supervision of WSP. Due to access constraints, the ground investigation was undertaken in phases. To date, three phases have been completed. The initial phase was undertaken between 4 November and 2 December 2013. The second phase was undertaken between 6 January and 17 January 2014 and the third phase was undertaken between 10 May and 17 May 2014. All works have been undertaken in general accordance with BS EN: 1997-2:2007 [2].

Site investigation works undertaken to date are presented in a Factual Report prepared by Geotechnics Limited [8] which is presented as Appendix B of this document. The report includes an exploratory hole drawing, exploratory hole records, photographs and in-situ and laboratory tests results. For ease of reference, an exploratory hole location plan has been presented as Drawing GEO-PC135450-01(1) in Appendix A.

The three phases of ground investigation completed to date have comprised the following:

27 No. cable percussive boreholes to depths of between 4.82m and 25m bgl;

13 No. cable percussive boreholes with rotary core follow-on to 15m bgl;

10 No. cone penetration tests (CPTs) to between 5m and 20m bgl;

64 No. machine excavated trial pits;

11 No. plate load tests;

13 No. soakaway tests;

7 No. road cores;

23 No. Dynamic Cone Penetrometer (DCP) tests;

Groundwater and surface water sampling; and,

Groundwater monitoring.

3.2.2 In Situ Testing

Standard Penetration Testing

Standard Penetration Tests (SPTs) were performed within the cable percussive boreholes. The results are presented on the exploratory hole records provided in Appendix 4 of the Geotechnics Factual Report.

Dynamic Cone Penetrometer

Thirteen DCP tests were undertaken at the locations shown on Drawing Geo-PC135450-001(1) in Appendix 8 of the Geotechnics Factual Report [8].

California Bearing Ratio (CBR) values were derived from the DCP data using the following relationship presented by the Highways Agency IAN 73/06 [9];

Log10 (CBR) = 2.48 - 1.057 (Log10) (mm/blow).



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Plots of cumulative blow count versus depth are presented in Appendix 10 of the Geotechnics Factual Report [8].

Hand Shear Vane

Hand Shear Vane (HSV) tests were undertaken, where possible, in the trial pits. The results of HSV testing are presented on the exploratory hole records in Appendix 6 of the Geotechnics Factual Report [8].

3.2.3 Laboratory Testing

Geotechnical Testing

A programme of geotechnical laboratory testing of soils was undertaken on selected samples recovered during the investigation described in Section 3.2.1. Soil testing was undertaken by Geotechnics Limited and Structural Soils in UKCAS accredited laboratories in accordance with the requirements of BS 1377:1990 parts 2-5, 7 and 8 [10, 11, 12, 13, 14, 15].

Rock testing was undertaken by Geotechnics Limited and MAT Testing Limited in a UKAS accredited laboratory in general accordance with ISRM Suggested Methods.

The following geotechnical laboratory tests were undertaken:

Moisture content;

Atterberg Limit;

Particle Size Distribution – by sieving and sedimentation;

Particle density;

Compaction – 2.5kg, 4.5kg and vibro compactive effort;

California bearing ratio;

Moisture condition value;

One dimensional consolidation;

Unconsolidated undrained triaxial;

Direct shear (using small shear box);

Consolidated undrained triaxial;

Point Load Strength; and,

Uniaxial Compressive Strength.

Soil Chemical Testing

A programme of chemical laboratory testing was undertaken on selected samples of soil recovered during the investigation described in Section 3.2.1. Chemical testing was undertaken by ALcontrol Laboratories and Derwentside Environmental Testing Services Limited in UKAS and MCERTS accredited laboratories.

The following laboratory tests were undertaken:

pH;

Metals – arsenic, cadmium, copper, chromium, chromium(VI), Mercury, Nickel, Lead, Selenium, Zinc (on a total and leachable basis);

Water soluble sulphate;

Total petroleum hydrocarbons (criteria working group) with benzene, toluene, ethylbenzene, xylenes;

Poly aromatic hydrocarbons (speciated);

Ammonium;



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Nitrate;

Nitrite;

Organochloride pesticides;

Organophosphorous pesticides;

Organic Matter Content;

SVOC and VOC;

Speciated Phenols; and,

Asbestos.

Water Chemical Testing

A programme of chemical laboratory testing was undertaken on selected samples of groundwater and surface water recovered during the investigation described in Section 3.2. Chemical testing was undertaken by ALcontrol Laboratories in a UKAS and MCERTS accredited laboratory.

The following laboratory tests were undertaken:

pH;

Metals – arsenic, cadmium, copper, chromium, chromium(VI), Mercury, Nickel, Lead, Selenium, Zinc;

Water soluble sulphate;

Total petroleum hydrocarbons (criteria working group) with benzene, toluene, ethylbenzene, xylenes;

Poly aromatic hydrocarbons (speciated);

Ammonium;

Nitrate;

Nitrite;

Semi volatile organic compounds and volatile organic compounds; and,

Hardness (surface water only).

The results of the laboratory testing have been presented in Appendix 14-16 of the Geotechnics Factual Report [8].



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4 GROUND SUMMARY

4.1 GENERAL

The following section summarises the ground conditions encountered along the preferred route.

An extract of the BGS Map Sheet 185 [5] overlain by the preferred route has been included as Figure 1 in Appendix A. In addition, long sections annotated with geological observations have been presented as Drawings ENV/39880/01/S1-S3 in Appendix D.

4.2 GROUND SUMMARY

The recent ground investigation has confirmed the general geological sequence outlined in Section 2.3. Table 4.1 provides a ground summary based on all the site investigation data available.

Given the similarities between the Upper Lias and the Marlstone Rock Beds and their proximity to one another in the lithological sequence, for the purposes of an engineering assessment any soil has been considered to represent the Upper Lias and any rock to represent the Marlstone Rock Beds.

Table 4.1 – Summary of Strata Stratum Code Typical Description Occurrence*

Made Ground – Historical Landfill

MG Soft and firm sandy/gravelly clay. Fine to coarse sand and fine to coarse gravel of brick, concrete and road planings. With cobbles and boulders (600-1200mm) of concrete.

Associated with Dodmoor Farm Landfill between Ch725 and Ch900m.

Made Ground - General

MG Clayey sandy fine to coarse gravel with occasional cobbles of flint. Soft to stiff, sandy/gravelly clay. Very soft and soft organic clay containing charcoal and ash.

Encountered only in historical exploratory holes.

Topsoil TS Soft, brown, sandy / gravelly clay. Fine to coarse, angular to rounded gravels. Occasionally with a low cobble content.

Almost all exploratory boreholes and trial pits.

Alluvium Al Very soft to firm, sandy, peaty in places, clay with some shells and decomposed organic remains. Clayey fine to coarse sand with subangular to subrounded gravel. Angular to rounded gravel of flint, shale, sandstone, mudstone and limestone.

Encountered in recent exploratory holes adjacent to Wilton Brook. Localised deposits encountered in historical exploratory holes between the West Coast Main Line and Wilton Brook (Ch610-Ch990m).

Granular Glacial Deposits

GGT Loose to very dense, silty/clayey sand/gravel predominantly comprising angular to rounded flint, chalk, sandstone, ironstone and limestone. With cobbles and boulders of limestone and flint. Localised bands/lenses of clay.

Encountered as localised bands in exploratory holes between Ch55m and Ch840m. Encountered in exploratory holes north of Upper Heyford between Ch4880m and 5380m.

Cohesive Glacial Deposits

CGT Soft to stiff, sandy/gravelly clay with fine to coarse subangular to rounded gravel of flint, limestone, chalk, sandstone and ironstone. Some cobbles and boulders of flint. Soft to firm silt. Some partings/lenses of sand.

Encountered in exploratory holes between Ch0m and Ch1710m. Encountered in exploratory holes north of Upper Heyford between Ch4880m and 6100m.



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Stratum Code Typical Description Occurrence*

Upper Lias (Whitby Formation)

UL Firm and stiff, grey, orangish brown, yellowish brown and light brown mottled, sandy / gravelly in places, micaceous, calcareous, silt / clay occasionally grading to siltstone / mudstone and occasionally containing bands of limestone. Occasionally described as friable, containing trace fossils and fissured. Shear surfaces described in five exploratory holes over the recent and historical site investigations.

At surface between Ch1940m and Ch3785m. Thickness is variable from <1.0m to 10m. Shear surfaces are described in historical exploratory holes BH51, BH53, BH57, BH62 and TP84.

Marlstone Rock Beds

MRB Medium strong and strong, fossiliferous or bioclastic, ferruginous limestone interbedded with extremely weak to weak mudstone, siltstone and sandstone.

Encountered at surface or underlying the Upper Lias between Ch1920m and Ch3875m.

Middle Lias (Dyram Formation)

ML Soft to very stiff, bluish grey, dark grey, orangish brown, sandy / gravelly in places, calcareous, silt / clay grading to siltstone / mudstone and containing bands of limestone. Frequently described as laminated and fissured. Shear surfaces described in seven exploratory holes over the recent and historical site investigations.

Underlying the entire route. At surface or underlying drift soils between Ch0m and Ch1920m, Ch3875m and Ch6100m. Shear surfaces are described in SATP03, SATP06A and historical exploratory holes BH32, BH39, BH43, BH129 and TP95.

* - Chainages given are approximate and based on available site investigation data.

Shear surfaces have been described in the Upper and Middle Lias deposits in a number of the recent and historical exploratory boreholes and trial pits at depths of between 0.75m and 29.25m bgl. The main areas in which these features have been described are between chainages 700-1100m and chainages 1400-2000m.



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5 EARTHWORKS AND STRUCTURES

For ease of assessment the route has been divided into a series of Earthworks Sections and Structures. Tables 5.1 and 5.2 provide a summary of ground conditions encountered at each Earthworks Section and Structure. These tables should be reference in conjunction with the long section information annotated with geological observations presented as Drawings ENV/39880/01/S1-S3 in Appendix D.



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Table 5.1 – Earthworks summary

EW Section Proposed Elevations (m AOD) Ground Conditions

Reference Chainage Proposed Earthworks Min Max Stratum Code Max Proven Depth to Base (m)

Max Thickness (m) Comments

EW1 0-160m At grade and low 1.5m) embankment

117.5 122.5 TS 0.25 0.25 Deeper Made Ground may be encountered closer to the former Petrol Filling Station.

MG 0.3* 0.3*

CGT / GGT 10 9.7

EW2 160-440m Maximum 6.5m high embankment

105 117.5 TS 0.3 0.3

CGT 7.9 7.6

ML +15 +7.1


85 105 TS 0.5 0.5

MG 4.2 4.1

Al 4.3 4.1

CGT / GGT 8.5 8.2

ML +24.5 +23.3

EW4 440-1248m 3-5m high embankment - - TS 0.4 0.4

MG 4.2 4.1

CGT 4.1 3.7

ML +15.45 +15.35

EW5 1248-1580m Maximum 6.0m deep cutting

88.5 98 TS 0.3 0.3

CGT 8.7 8.4

ML +15 +6.3


98 103.5 TS 0.3 0.3 MRB not proven in this section. Presence extrapolated from EW Section7.

CGT 2.6 2.3

UL +1.2 +0.9

MRB - -

ML +15 +14.7



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EW Section Proposed Elevations (m AOD) Ground Conditions

Reference Chainage Proposed Earthworks Min Max Stratum Code Max Proven Depth to Base (m)

Max Thickness (m) Comments

EW7 2010-3995m Maximum 10m deep cutting

87 103.5 TS 0.4 0.4

GT 1.0 0.6

UL 10 9.6

MRB 11 10.8

ML +15 +14.9


78 88 TS 0.8 0.8

CGT 2.0 1.9

ML +20 +19.95

EW9 4520-4750m At grade and low ( 2m) embankment

88 90 TS 0.3 0.3

ML +10 +9.7

EW10 4750-5515m Maximum 7.1m deep cutting

78.5 90 TS 0.4 0.4

CGT / GGT 29.25 28.85

ML +36.7 +8.5

EW11 5515-6100m At grade, shallow 1.5m) cutting and

maximum 3.0m high embankment

80 86 TS 0.4 0.4

CGT +4.0 +3.7

ML +10 +8.5



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Table 5.2 – Structure summary

Structure Ground Conditions

Reference Chainage Structure Details Adjacent Earthworks Stratum Code Max Proven Depth to Base (m)

Maximum Thickness (m)

Comments

STR7001 585m Bridge over the West Coast Main Line Approx. 32m span

EW3 Proposed elevation c.100m AOD

TS 0.4 0.4

CGT 8.5 8.2

ML +25 +23

STR7002 700m Bridge over the Grand Union Canal Approx. 36m span


TS 0.5 0.5

CGT 3.5 3.1

ML +25 +23.8

STR7003 990m Bridge over Wilton Brook Approx. 23m span


TS 0.25 0.25 Require completion of site investigation for confirmation of ground conditions

Al 4.3 4.05

ML +20 +19.5

STR7004 2740m Brockhall Road overbridge Approx. 34m span


TS 0.4 0.4

UL 1.5 1.2

MRB 8.2 6.7

ML +15 +6.8

STR7005 3510m Brington Road overbridge Approx. 34m span


TS 0.3 0.3

UL 2.9 2.85

MRB 9.1 8.8

ML +15 +6

STR7006 4220m Bridge over Hollandstone Brook and Hollandstone Farm access track

EW8 Proposed elevation c.82.5m AOD

TS 0.4 0.4

ML +20 +19.95

STR7007 5240m Upper Heyford Farm over bridge

EW10 TS 0.4 0.4

CGT / GGT 29.25 28.85

ML +25 +8.5

STR7008 4220m Hollandstone Farm access bridge

None TS 0.45 0.45

ML +20 +19.95



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6 MATERIAL PROPERTIES

6.1 GENERAL

The various strata underlying the route have been summarised in Section 4. The following section discusses the material properties for the different strata based on data from the various phases of field investigation and laboratory testing described in Sections 2 and 3.

6.2 CHARACTERISTIC PARAMETERS

Where necessary, determination of characteristic parameters has been based on a cautious estimate of results derived from laboratory testing, published correlations and field tests, complemented with engineering judgement. Where material parameters are assumed, derived by calculation, or taken from published sources, further details are provided as to their derivation.

The following is a list of correlations used to support the derivation of characteristic parameters.

Undrained cohesion (cu) has been estimated based on SPT N60 and plasticity data using relationships set out by Stroud [16].

= … ( / ) where: ƒ1 is unitless and based on the soil’s plasticity

Effective angle of shearing resistance ( ’) for granular soils has been estimated based on SPT (N1)60 using relationships set out by Peck [17]

Effective angle of shearing resistance for cohesive soils has been estimated based on plasticity data as set out in BS 8002:1994 [18].

Residual angle of shearing resistance ( r’) has been estimated based on plasticity data using relationships set out by Skempton et al. [19].

Vertical drained Young’s Modulus (E’) for cohesive soils has either been estimated based on cu, using relationships set out by Stroud et al. [16], or SPT N60 and plasticity data using relationships set out in CIRIA 143 [20].

= × … ( / )

Vertical drained Young’s Modulus for granular soils has been estimated based on SPT N60 as set out in CIRIA 143 [20].

= × … ( / )

Vertical drained Young’s Modulus for the Marlstone Rock Beds has been estimated based on a conservative assessment of the unconfined compressive strength as set out in CIRIA 181 [24].

= ( ) . … ( / )

California Bearing Ratio (CBR) for cohesive soils has been estimated based on plasticity, as set out in HA IAN 73/06 [21], and undrained shear strength as set out by Black et al. [22].

= × … ( / )

Unconfined compressive strength (UCS) has been estimated based on SPT N60 using relationships set out in CIRIA 143 [20].

6.3 EARTHWORKS TESTING

To appropriately assess materials suitability for reuse, moisture content/dry density relationship, California Bearing Ratio (CBR) and Moisture Condition Value tests were undertaken on recompacted samples from



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the field. These tests were undertaken at varying moisture contents such that moisture content limits, defining a suitable material, could be determined. These limits were based on achieving the following:

An air voids content of <10%;

A dry density of 90-95% (depending upon the compactive effort used);

A minimum CBR of 3%; and,

An MCV of 8.

General material classification has been assessed based on characteristic properties and guidance set out in SHW Volume 1 Series 600 [23].

6.4 TOPSOIL

Topsoil was encountered in the majority of exploratory boreholes and trial pits to a maximum depth of 0.5m. Topsoil stripped from site is likely to be suitable for reuse as a Class 5 material on cutting and embankment side slopes. Topsoil materials stockpiled for reuse should be stored in accordance with Appendix 6/8 of SHW Volume 1 Series 600 [23].

Chemical analysis undertaken on selected samples of Topsoil recovered from the site investigation reveal water soluble sulphate concentrations of <1.5mg/l to 40mg/l and pH values of between 6.35 and 8.45.

6.5 MADE GROUND

6.5.1 Occurrence and Description

The recent investigation encountered Made Ground associated with Dodmoor Farm Landfill; a historical landfill site thought to have been used for the disposal of wastes during the construction of the M1. Borehole BH07 suggests that the Made Ground extends to a maximum of 4.2m bgl. The material encountered ranged from low to high shear strength cohesive and medium dense to very dense granular materials containing cobbles and boulders of concrete. Under current proposals it is likely that this Made Ground would be encountered at formation level under the northern embankment of the route between Ch725m and Ch900m within Earthworks Section 3.

Historical investigation data indicates;

Localised Made Ground between Ch725m and Ch825m and south of the Dodmoor Farm landfill. Exploratory hole records describe soft and firm cohesive and granular soils, with no anthropogenic materials, extending to a maximum of 1.8m bgl. Under current proposals it is likely that these materials would be encountered as localised features at formation level below the southern embankment within these chainages.

Localised Made Ground between Ch925m and Ch1250m. Exploratory hole records describe very soft organic soils containing charcoal and ash up to 2.9m deep. Under current proposals these materials may be encountered around the Wilton Brook crossing.

Given the variable nature of the Made Ground soils the derivation of characteristic values of shear strength and stiffness is not considered appropriate.

6.6 ALLUVIUM


Alluvium was encountered locally in the historical site investigation between chainages 611m and 1200m, associated with the Grand Union Canal and Wilton Brook. These deposits extended to a maximum depth of 4m bgl and consisted of both cohesive (very soft to firm sandy, peaty in places, clay) and granular (angular to rounded gravels) materials.



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To date, Alluvium has not been encountered during the recent investigation and given the general lack of data, the derivation of characteristic values of shear strength and stiffness is not considered appropriate. This will be reviewed once the outstanding investigation is completed.

6.7 COHESIVE GLACIAL TILL


Cohesive Glacial Till was encountered mantling the valley slopes at the western end of the route between Ch0m and Ch1710m. These deposits extend to a maximum depth of 9.5m bgl and tend to thin towards the valley base around Wilton Brook.

Towards the eastern end of the route, Cohesive Glacial Till was also encountered in a deep glacial channel which extends to a maximum proven depth of 29.25m bgl.

The Cohesive Glacial Till generally comprises brown, soft to stiff clay / silt of intermediate and high plasticity (CI, CH, MI, MH) with secondary fractions of sand and gravel. The gravel element generally comprises subangular to rounded flint, limestone, chalk, sandstone and ironstone. Figure 6.1 presents natural moisture content (NMC), liquid limit (LL) and plasticity index (PI) versus depth. A characteristic plasticity index for the Cohesive Glacial Till of 25% is suggested.

6.7.2 Shear Strength

Total Stress

The undrained shear strength (cu) of the Cohesive Glacial Till has been assessed using a combination of field and laboratory testing. A total of one hundred and five hand shear vane tests were undertaken during the recent investigation, giving a range of cu values between 20kN/m2 and 120kN/m2.

Twenty five SPTs were undertaken during the recent investigation. Tests returned N60 values of between 5 and 27 which indicate cu values of between 25kN/m2 and 135kN/m2.

Twenty nine quick undrained triaxials were carried out on ‘undisturbed’ U100 samples taken over both the recent and historical investigations. Tests gave a range of cu values of between 16kN/m2 and 265kN/m2.

A composite plot of the field and laboratory testing data has been presented as Figure 6.2. Based on this plot, a characteristic cu of 45kN/m2 has been estimated between 0.5m and 1.5m bgl. From 1.5m bgl the cu is considered to increase linearly from 65kN/m2 to 170kN/m2 at 14m bgl and then remaining at 170kN/m2 thereafter.

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7

8

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Dep

th (m

)

(%)

Figure 6.1MC versus Depth (CGT)

NMC LL PI



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Effective Stress

The drained shear strength of the Cohesive Glacial Till has been appraised based on laboratory consolidated undrained triaxial (CUT) tests and direct shear tests. A total of eighteen CUTs have been undertaken on the Cohesive Glacial Till over the recent and historical investigations. Analysis of the results, assuming plane strain conditions, reveals a peak angle of shearing resistance ( ’p) of 27° and an effective cohesion (c’) of 5kN/m2. The results of these tests are presented on Figure 6.3.

Ten direct shear tests have been undertaken over the recent and historical investigation. Analysis of the results suggests ’p = 32° and c’ = 7.5kN/m2. Constant volume shear strength parameters of ’cv = 26° and c’ = 5kN/m2 are suggested (see Figure 6.4).

Guidance given in BS 8002:1994 [18] suggests a ’cv = 26° for a material with a PI of 24%.

Based on the above, a characteristic ’cv of 26° and c’ of 0.5kN/m2 are suggested for design purposes.

6.7.3 Stiffness and Compressibility

Stiffness parameters for the Cohesive Glacial Till have been assessed based on both field and laboratory testing data. Nine one dimensional consolidation tests have been undertaken on the Cohesive Glacial Till

0

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16

0 50 100 150 200 250 300

Dep

th (m

)

cu (kN/m2)

Figure 6.2Undrained Shear Strength versus Depth (CGT)

QUT SPT N60 HSV

0

50

100

150

200

250

300

0 100 200 300 400 500

t'(k

N/m

2 )

s' (kN/m2)

Figure 6.3Stress Path Parameters s' versus t' (CGT)

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200

250

300

350

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450

0 50 100 150 200 250 300

(kN

/m2 )

N (kN/m2)

Figure 6.4Normal Stress versus Shear Stress (CGT)

Constant Volume Peak



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over the recent and historical investigations. The results give coefficient of volume compressibility (mv) values between 0.03m2/MN and 0.14m2/MN for a stress range of between 20kN/m2 and 240kN/m2. Based on E’ = 1/mv, values of drained Young’s Modulus (E’) of between 7MN/m2 and 33MN/m2 are calculated.

Correlations with SPT N60 suggest a range of E’ values from 3.5MN/m2 to 23MN/m2.

A composite plot of the field and selected laboratory testing data is presented as Figure 6.5. Based on this a characteristic drained modulus of 11MN/m2 is proposed at 1m bgl, increasing linearly to 23MN/m2 at 5m bgl and then remaining at 23MN/m2 thereafter.

6.7.4 Earthworks

California Bearing Ratio at Grade

Three dynamic cone penetration (DCP) tests were undertaken in the Cohesive Glacial Till around chainage 0m. The tests returned equivalent CBR values of between 2.5% and 8.5%.

Plate load tests were undertaken in trial pits TP61, TP62 and TP64 at depths of between 0.5m and 1.0m bgl. The results of the tests indicate equivalent CBR values of between 1.9% and 2.6%.

Laboratory CBR tests undertaken on samples at natural moisture content (NMC) returned values of between 0.5% and 13%.

Based on the suggested characteristic undrained shear strength, a CBR value of around 1.3% is indicated. At this stage it may be prudent to assume a CBR of <2.5% for the Cohesive Glacial Till where anticipated at Grade (i.e. approximate chainages Ch30-160m, Ch1260, Ch1580 and Ch5700m).

Use as Fill Material

Based on the grading, plasticity and moisture content of the Cohesive Glacial Till, it is considered that the majority of the samples would be classified as Class 2 in accordance with SHW Volume 1 Series 600 [24].

Laboratory compaction, CBR and MCV testing is summarised on Figures 6.6 and 6.7.

To achieve the performance criteria outlined in Section 6.3, upper and lower bound moisture contents of 13% and 21% are suggested.

NMC data (Figure 6.1) shows that a proportion of the Cohesive Glacial Till samples tested exceed the upper bound limit and will, therefore, require conditioning prior to reuse.

0

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14

0 10 20 30 40 50 60 70

Dep

th (m

)

E' (MN/m2

Figure 6.5Undrained Stiffness versus Depth (CGT)

SPT N60 Oed



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6.7.5 Sulphate Analysis

Chemical analysis undertaken on selected samples of Topsoil recovered from the site investigation reveal water soluble sulphate concentrations of <1.5mg/l to 64mg/l and pH values of between 6.5 and 8.5.

6.8 GRANULAR GLACIAL TILL


Granular Glacial Till was encountered as localised lenses within the Cohesive Glacial Till mantling the valley slopes at the western end of the route, between Ch0m and Ch1710m.

Towards the eastern end of the route, Granular Glacial Till was also encountered in a deep glacial channel which extends to a maximum proven depth of 29.25m bgl.

Granular materials generally comprise loose to very dense sand / gravel with secondary fractions of silt and clay. Coarser materials predominantly comprise angular to rounded flint, chalk, sandstone, ironstone and limestone. The recorded natural moisture content of the Granular Glacial Till ranges from 8% to 24% and is presented as a plot of NMC versus depth on Figure 6.8.

1.4

1.5

1.6

1.7

1.8

1.9

2

0 5 10 15 20 25 30 35

d(M

g/m

3 )

Moisture Content (%)

Figure 6.6Dry Density versus Moisture Content (CGT)

Dry Density Dry Density at NMC Maximum Dry Density

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0 5 10 15 20 25 30 35

MCV

CBR

(%)


Figure 6.7CBR & MCV versus Moisture Content (CGT)

CBR Top CBR Base MCV

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8

9

0 5 10 15 20 25 30

Dep

th (m

)

MC (%)

Figure 6.8Moisture Content versus Depth (GGT)



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The effective angle of shearing resistance of the Granular Glacial Till has been appraised based on SPT tests and laboratory direct shear tests. A total of ninety SPTs were undertaken as part of the recent and historical investigations which produced results ranging from 5 to >100 between depths of 1.5m and 28m bgl. A plot of SPT N versus depth for both the recent and historical investigations has been presented as Figure 6.9.

Five direct shear tests were undertaken over the recent and historical investigations. Analysis of the results suggests ’p = 35° (Figure 6.10).

Based on this data a ’p of 33° is proposed between 1.5m bgl and 25m bgl.


Drained Young’s Modulus (E’) has been assessed based on SPTs undertaken in the recent and historical investigations. Based on this, a characteristic modulus of 36MN/m2 is proposed between 1.5m bgl and 25m bgl, increasing to 50MN/m2 below this depth.

6.8.4 Earthworks


Based on a total of seventeen particle size distribution tests, approximately 25% of the Granular Glacial Till samples would be classified as Class 1A/1B, 50% as Class 2A/2B and 25% as Class 2C in accordance with SHW Volume 1 Series 600 [24]. Whilst the material is classed as a granular soil in terms of the geotechnical model, the significant proportion of fine material defines it as a predominantly cohesive fill in terms the SHW Volume 1 Series 600 [24].

Laboratory compaction, CBR and MCV testing are summarised on Figures 6.11 and 6.12.

In order to achieve the performance criteria outlined in Section 6.3, upper and lower bound moisture contents of 8% and 13% are suggested.

Natural moisture content (NMC) data (Figure 6.8) shows that a proportion of the Granular Glacial Till samples tested exceed the upper bound limit and will, therefore, require conditioning prior to reuse. The material appears to be very sensitive to moisture content with CBR values falling markedly once the OMC has been exceeded. The reason for this may be related to the relatively high silt fractions in the samples tested (12-32%).

0

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25

30

0 10 20 30 40 50 60 70 80 90 100

Dep

th (m

)

SPT (N1)60 (values >100 omitted for clarity)

Figure 6.9SPT N60 versus Depth (GGT)

SPT N160 SPT N1

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80

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120

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0 50 100 150 200

(kN

/m2 )

N (kN/m2)

Figure 6.10Normal Stress versus Shear Stress (GGT)



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6.9 UPPER LIAS (WHITBY MUDSTONE FORMATION)


The Upper Lias is considered to underlie the alignment between chainages 1940m and 3785m and will be in cutting slopes and at formation level within Earthworks Section 7.

Where encountered, the Upper Lias predominantly comprises firm and stiff grey, orangish brown and yellowish brown, sandy / gravelly in places, micaceous, calcareous silt / clay of intermediate and high plasticity (CI, CH, MH), occasionally grading to siltstone / mudstone and with localised horizons of limestone and sandstone. Gravels generally comprise mudstone lithorelicts. Figure 6.13 presents a plot of NMC, liquid limit and plasticity index versus depth. A characteristic PI for the Upper Lias of 26% is suggested.

During the historical investigation, shear surfaces have been described in the Upper Lias generally between Ch1400m and Ch2200m to the south and outwith the proposed alignment corridor. Based on the recent investigation, Upper Lias deposits are not considered to be present within the above chainages.

1.5

1.6

1.7

1.8

1.9

2

2.1

2.2

2.3

0 5 10 15 20 25

d(M

g/m

3 )


Figure 6.11Dry Density versus Moisture Content (GGT)


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0 5 10 15 20 25

MCV

CBR

(%)


Figure 6.12CBR & MCV versus Moisture Content (GGT)


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Dep

th (m

)

%

Figure 6.13NMC, LL and PI versus Depth (UL)

NMC LL PI



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Total Stress The undrained cohesion of the Upper Lias has been assessed using a combination of field and laboratory testing. However, the gravelly and fissured nature of the Upper Lias made it difficult to recover ‘undisturbed’ samples for laboratory testing.

A total of twenty nine hand shear vane tests have been undertaken during the recent investigation. Tests were undertaken on samples taken from between 0.3m and 3.0m bgl and record a range of cu values between 40kN/m2 and 109kN/m2.

Twenty four SPTs have been undertaken during the recent investigation. Tests were carried out at depths of between 1.2m and 5.7m bgl and returned N60 values of between 9 and >100 which indicate cu values of between 42kN/m2 and >300kN/m2. An upper limit of 300kN/m2 has been placed on the cu to account for discrete bands of rock within the stratum.

Three quick undrained triaxials were carried out on ‘undisturbed’ U100 samples taken over both the recent and historical investigations. Tests were carried out on samples taken at depths of between 1.2m and 3.85m bgl and give a range of cu values of between 68kN/m2 and 190kN/m2. A composite plot of the field and laboratory testing data is presented as Figure 6.14.

Based on this plot, a characteristic cu of 55kN/m2 is proposed for the Upper Lias at 0.5m bgl, increasing linearly to 110kN/m2 at 3.0m bgl and then remaining at 110kN/m2 thereafter.

Effective Stress

The drained shear strength of the Upper Lias has been appraised based on laboratory consolidated undrained triaxial (CUT) tests and direct shear tests. A total of four CUTs were undertaken on the Upper Lias over the recent and historical investigations. Analysis of the results, assuming plane strain conditions, indicate a peak angle of shearing resistance ( ’p) of 27°. The results of these tests were presented on Figure 6.15.

Five direct shear tests were undertaken over the recent and historical investigation and are shown on Figure 6.16. Analysis of the results suggests ’p/ ’cv = 27°, c’ = 10kN/m2 and ’r = 14°.

Guidance given in BS 8002:1994 [18] suggests ’cv = 26° for a material with a plasticity of 26%. Relationships set out by Skempton, et al. [19] suggests ’r = 14° for a material with a plasticity of 24%.

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6

0 50 100 150 200 250 300

Dep

th (m

)

cu (kN/m2)

Figure 6.14Undrained Shear Strength versus Depth (UL)

HSV SPT QUT



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Based on the above the following effective shear strength parameters are suggested for design purposes:

A characteristic ’cv of 26° and c’ of 0.5kN/m2

A characteristic ’r of 14° and c’ of 0kN/m2


The stiffness of the Upper Lias has been assessed based on cu and Ip. A characteristic E’ of 13MN/m2 is proposed at 0.5m bgl, increasing linearly to 25MN/m2 at 3.0m bgl and then remaining at 25MN/m2 thereafter.

6.9.4 Earthworks


Four dynamic cone penetration (DCP) tests were undertaken in the Upper Lias between chainages 4100m and 4200m. These tests returned equivalent CBR values of between 4.8% and 11.8%.

Plate load tests were undertaken in trial pits TP30, TP31, TP32, TP46 and TP47 at depths of between 0.5m and 1.0m bgl. The results of the tests indicate equivalent CBR values of between 1.2% and 2.3%.

Laboratory CBR tests undertaken on samples at natural moisture content (NMC) returned values of between 5.4% and 17%.

Based on the suggested characteristic undrained shear strength, a CBR value of around 1.7% would be suggested. At this stage it may be prudent to assume a CBR of <2.5% for the Upper Lias at Grade (i.e. approximate chainages Ch2011m and Ch3940-4011m).


Based on the grading, plasticity and moisture content of the Upper Lias, the samples tested would be classified as Class 2 in accordance with SHW Volume 1 Series 600 [24].

Laboratory compaction, CBR and MCV testing is summarised on Figure 6.17 and Figure 6.18.


Natural moisture content (NMC) data (Figure 6.13) shows that a proportion of the Upper Lias samples tested exceed the upper bound limit and will, therefore, require conditioning prior to reuse.

0

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0 20 40 60 80 100 120 140 160 180

t' (k

N/m

2)

s' (kN/m2)

Figure 6.15Stress Path Parameters s' versus t' (UL)

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0 20 40 60 80 100 120

(kN

/m2)

N (kN/m2)

Figure 6.16Normal Stress versus Shear Stress (UL)

Peak Data Residual Data



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Chemical analysis undertaken on selected samples of Topsoil recovered from the site investigation record water soluble sulphate concentrations of <1.5mg/l to 1315mg/l and pH values of between 7 and 8.7.

6.10 MARLSTONE ROCK BEDS


The Marlstone Rock Beds underlie the Upper Lias deposits and it is anticipated that that these deposits will be encountered in cutting slopes and at formation level between chainages 1920m to 3875m.

Where encountered, the Marlstone Rock Beds predominantly comprise medium strong and strong ferruginous limestone inter-bedded with extremely weak to weak mudstone, siltstone and fine and medium grained sandstone. Any soils which may represent weathered strata of the Marlstone Rock Beds have been considered as part of the Upper Lias for the purposes of this assessment.

6.10.2 Unconfined Compressive Strength

The unconfined compressive strength (quc) of the Marlstone Rock Beds has been assessed based on both field and laboratory testing data. Twenty nine SPTs were undertaken during the recent investigation. Tests were carried out at depths of between 1.2m and 7.5m bgl and returned N60 values of between 22 and 868, which suggest quc values of between 0.2MN/m2 and 8.7MN/m2.

Ten direct unconfined compressive strength tests were undertaken on core samples recovered from exploratory boreholes at depths of between 3.9m and 8.7m bgl with recorded quc values of between 0.2MN/m2 and 28MN/m2.

A total of forty nine axial point load tests were undertaken on samples recovered from exploratory boreholes at depths of between 3.3m and 9.0m bgl with recorded point load index (Is(50)) values of between 0.007 and 2.3, which suggest quc values of between 0.1MN/m2 and 33.5MN/m2. A cumulative plot of quc versus depth is presented as Figure 6.19.

Due to the variable strength and interbedded nature of the Marlstone Rock Beds, it would not be appropriate to assign a characteristic strength to the rock mass. Table 6.1 summarises the quc values for each lithology.

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d(M

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Figure 6.17Dry Density versus Moisture Content (UL)


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MCV

CBR

(%)


Figure 6.18CRB & MCV versus Moisture Content (UL)




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6.10.3 Stiffness

Estimates of drained Young’s Modulus (E’) for the various lithologies comprising the Marlstone Rock Beds have been made based a conservative view of the quc. Characteristic E’ values have been presented in Table 6.1.

Table 6.1 – Summary of laboratory strength testing on the Marlstone Rock Beds

Lithology Min quc (MN/m2)

Max quc (MN/m2)

Characteristic quc (MN/m2)

Characteristic E’ (MN/m2)

Comments

Limestone 3 33.5 7 480 Is(50) correction factor (k) = 14.6

Mudstone 0.2 11 0.4 95 Is(50) correction factor (k) = 12.4

Siltstone 0.1 1.3 0.4 95 Is(50) correction factor (k) = 5

Sandstone 0.2 8.7 0.75 150 Based on SPT data only

6.10.4 Earthworks

Based on the sample size from the cored boreholes, earthworks testing was not undertaken. However, it is reasonable to assume that appropriately processed limestone and sandstone could be suitable for reuse as a Class 1 material. Should durability criteria be met, as set out in SHW Volume 1 Series 600 [23], the limestone may also be suitable for reuse as a Class 6 material.

It is likely that the majority of the mudstone and siltstone would be suitable for reuse as a Class 2 material following any appropriate processing and conditioning. Further testing at source is recommended to validate the above comments.

6.11 MIDDLE LIAS (DYRHAM FORMATION)


Middle Lias deposits are considered to underlie the entire alignment. This formation has been encountered at surface or directly underlying Made Ground and drift soils between Ch0-1920m and Ch3875-6100m.

Where encountered the Middle Lias predominantly comprises soft to very stiff bluish grey, dark grey and orangish brown, sandy / gravelly in places, calcareous, fissured and micaceous, silt / clay of low to high plasticity (CL, CI, CH), grading to extremely weak to weak mudstone / siltstone. Mudstone lithorelicts/inclusions were frequently described, along with horizons of strong limestone and occasional

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Dep

th (m

)UCS (MN/m2)

Figure 6.19UCS versus Depth (MRB)

Equivalent UCS Siltstone Equivalent UCS MudstoneUCS Mudstone SPTEquivalent UCS Limestone UCS LimestoneUCS Siltstone



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horizons of sandstone. Figure 6.20 presents a plot of NMC, liquid limit and plasticity index versus depth. A characteristic plasticity index for the Middle Lias of 21% is suggested.

During the recent and historical investigations, shear surfaces were described in the Middle Lias between chainages 700m and 1100m at depths of between 0.75m and 2.1m bgl.


Total Stress The undrained cohesion of the Middle Lias has been assessed using a combination of field and laboratory testing. A total of twenty nine hand shear vane tests were undertaken during the recent investigation. Tests were undertaken on samples from between 0.45m and 3.5m bgl with a recorded range of cu values between 17kN/m2 and 116kN/m2.

One hundred and sixty eight SPTs were undertaken during the recent investigation. Tests were carried out at depths of between 1.2m and 24.5m bgl and returned N60 values of between 7 and >100 which indicate cu values of between 37kN/m2 and >300kN/m2. An upper limit of 300kN/m2 has been placed on the cu to account for discrete bands of rock within the stratum.

Ninety one quick undrained triaxials were carried out on ‘undisturbed’ U100 samples taken during the recent and site investigation. Tests were carried out on samples taken at depths of between 0.9m and 29.8m bgl and give a range of cu values of between 32kN/m2 and >300kN/m2.

A composite plot of the field and laboratory testing data is presented as Figure 6.21. Based on this plot, a characteristic cu of 45kN/m2 has been estimated at 1.0m bgl, increasing linearly to 140kN/m2 at 12.0m bgl and then remaining at 140kN/m2 thereafter.

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0 10 20 30 40 50 60 70

Dep

th (m

)

(%)

Figure 6.20NMC, LL and PI versus Depth (ML)

NMC PI LL



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Effective Stress

The drained shear strength of the Middle Lias has been appraised based on laboratory consolidated undrained triaxial (CUT) tests and direct shear tests. A total of eight CUTs were undertaken on samples from the Middle Lias over the recent and historical investigations. Analysis of the results, assuming plane strain conditions, indicates a peak angle of shearing resistance ( ’p) of 30° and an effective cohesion (c’) of 10kN/m2. The results of these tests are presented on Figure 6.22.

Nine direct shear tests were undertaken over the recent and historical investigation and the results are shown on Figure 6.23. Analysis of the results suggests a ’p = 27° and c’ = 15kN/m2. Constant volume shear strength parameters of ’cv = 25° and c’ = 5kN/m2 are suggested, together with a residual angle of shearing resistance ( ’r) of 16°.

Guidance given in BS 8002:1994 [18] suggests ’cv = 28° for a material with a plasticity of 21%. Relationships set out by Skempton, et al. [19] suggests ’r = 16° for a material with a plasticity of 21%.

Based on the above the following effective shear strength parameters are suggested for design purposes:

0

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8

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14

16

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20

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Dep

th (m

)

cu (kN/m2)

Figure 6.21Undrained Shear Strength versus Depth (ML)

QUT SPT N60 HSV

0

100

200

300

400

500

600

0 200 400 600 800 1000

t' (k

N/m

2)

s' (kN/m2)

Figure 6.22Stress Path Parameters s' versus t' (ML)

0

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200

250

0 50 100 150 200 250 300

kN/m

2)

(kN/m2)

Figure 6.23Normal Stress versus Shear Stress (ML)

Constant Volume Peak Residual



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A characteristic ’cv of 25° and c’ of 0.5kN/m2

A charactersitic ’r of 16° and c’ of 0kN/m2


Stiffness parameters for the Middle Lias have been assessed based on both field and laboratory testing data. Twenty, one dimensional consolidation tests have been undertaken on samples of the Middle Lias over the recent and historical investigations. The results record coefficient of volume compressibility (mv) values between 0.01m2/MN and 0.18m2/MN which indicate drained stiffness (E’) values of between 6MN/m2 and 110MN/m2.

Correlations with SPT N60 suggest a range of E’ values from 7MN/m2 to >500MN/m2. A composite plot of the field and selected laboratory testing data is presented as Figure 6.24. Based on this, a characteristic drained modulus of 12.5MN/m2 is proposed between 1.0m and 4.0m bgl, increasing to 22.5MN/m2 between 4.0m and 10.0m bgl, then increasing linearly to 75MN/m2 at 16.0m bgl and remaining at 75MN/m2 with increasing depth thereafter.

6.11.4 Earthworks


Four dynamic cone penetration (DCP) tests were undertaken in the Middle Lias between chainages 4600m and 4900m. These tests returned equivalent CBR values of between 4.9% and 10.9%.

Plate load tests were undertaken in trial pits TP52, TP53 and TP54 at depths of between 0.5m and 1.0m bgl. The results of the tests indicate equivalent CBR values of between 1.7 and 2.0.

Laboratory CBR tests undertaken on samples at natural moisture content (NMC) returned values of between 5.5% and 16%, though it should be noted that the dataset was small.

Based on suggested characteristic undrained shear strength, a CBR value of around 1.7% would be suggested. At this stage it may be prudent to assume a CBR of <2.5% for the Middle Lias at Grade (i.e. approximate chainages Ch4500-4600m and Ch4700-4760m).


Based on the grading, plasticity and moisture content of the Middle Lias, it is considered that the majority of the samples would be classified as Class 2 in accordance with SHW Volume 1 Series 600 [24].

Laboratory compaction, CBR and MCV testing is summarised on Figure 6.25 and Figure 6.26.

0

2

4

6

8

10

12

14

16

18

20

0 20 40 60 80 100 120 140 160 180 200

Dep

th (m

)

E' (MN/m2) (values >200 omitted for clarity)

Figure 6.24Drained Stiffness versus Depth (ML)

Oed SPT



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Natural moisture content (NMC) data (Figure 6.20) shows that a proportion of the Middle Lias samples tested exceed the upper bound limit and will, therefore, require conditioning prior to reuse.


Chemical analysis undertaken on selected samples of Topsoil recovered from the site investigation reveal water soluble sulphate concentrations of 14mg/l to 1140mg/l and pH values of between 5.9 and 8.4.

1.4

1.5

1.6

1.7

1.8

1.9

2

0 5 10 15 20 25 30 35

d(M

g/m

3 )


Figure 6.25Dry Density versus Moisture Content (ML)


0

2

4

6

8

10

12

14

16

18

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35

MCV

CBR

(%)


Figure 6.26CBR & MCV versus Moisture Content (ML)




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6.12 SUMMARY TABLE

Stratum Shear Strength Drained Stiffness, E’

(MN/m2) Earthworks

cu (kN/m2) c’ (kN/m2) cv’ (°) r’ (°) MC Bounds (%) CBR (%) EW Class

Made Ground - - - - - - - -

Alluvium - - - - - - - -

Cohesive Glacial Till 45kN/m2 between 0.5m and 1.5m

Increasing linearly from 65-170kN/m2 between 1.5-14m

170kN/m2 below 14m

0.5 26° - Increasing linearly from 11-23MN/m2 between 1.0-5.0m

23MN/m2 below 5.0m

13-21% At grade: <2.5%

Reworked: 3%

2A/2B

Granular Glacial Till - 0 33° from 1.5-25m

- 36MN/m2 from 1.5-25m 8-13% 3% 23% - 1A/1B

54% - 2A/2B

23% - 2C

Upper Lias Increasing linearly from 55-110kN/m2 between 0.5-3.0m

110kN/m from 3.0m

0.5 26° 14° Increasing linearly from 13-25kN/m2 between 0.5-3.0m

25kN/m from 3.0m

14-25% At grade: <2.5%

Reworked: 3%

2A/2B

Mar

lsto

ne R

ock

Bed

s

Limestone 7MN/m2 480 - - 1

Mudstone 0.4MN/m2 95 - - 2

Siltstone 0.4MN/m2 95 - - 2

Sandstone 0.75MN/m2 150 - - 1

Middle Lias Increasing linearly from 45-140kN/m2 between 1.0-12m

140kN/m2 from 12m

0.5 25° 16° 12.5MN/m2 from 1.0-4.0m

22.5MN/m2 from 4.0-10.0m

Increasing linearly from 22.5-75MN/m2 between 10.0-16.0m

75MN/m2 from 16.0m

13-25% At grade: <2.5%

Reworked: 3%

2A/2B

A45 Daventry Link Road Ground Investigation Report

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7 GEOTECHNICAL RISK REGISTER

7.1 GEOTECHNICAL RISK CLASSIFICATION

Chart 2 in Appendix C, Part 2 of Highways Agency document HD22/08 ‘Managing Geotechnical Risk’ describes the methodology to review a proposed scheme, identify the project complexity, assess the risks and thereby determine its Geotechnical Classification. The following table defines the different geotechnical categories.

Table 7.1 - Geotechnical Category Descriptions Geotechnical

Category Description

1 Involves minor geotechnical activities and/or risk and where the ground conditions are known from comparable experience to be sufficiently straightforward, such that simple or basic methods may be used for design and construction

2

Involves conventional types of earthworks structures and foundations with no abnormal risks or unusual or exceptionally difficult ground conditions; requires quantitative geotechnical data and analysis to ensure that fundamental requirements are satisfied, but routine procedures for field and laboratory testing and for design and construction may be used.

3 Involves very large or unusual structures, activities involving abnormal risks or unusual or exceptionally difficult ground or loading conditions; generally includes projects affected by contaminated land.

Taking into consideration the objectives of the assessment process, the available ground investigation and geotechnical information, and the envisaged construction requirements, this project is considered as falling into Geotechnical Category 2.

The Geotechnical Risk Register for the envisaged works is presented in Appendix E. The Risk Register includes aspects that, at this stage of the project, have been identified as having some relevance with respect to cost and Health and Safety. As the project progresses and more becomes known about the ground conditions and any design works that are proposed, the Risk Register should be updated. The Risk Register identifies geotechnical hazards/risks associated with proposed works and should be considered as a live document.

A simple rating of probability (1-5) has been included within the assessment of the original hazards and risks involved. A rating of (1) represents a negligible chance of the risk being realised, whereas 5 would indicate a very high chance. A rating of impact (1-5) is also included in the assessment, with a rating of (1) very low to (5) very high.

It should be noted that the Construction (Design and Management) Regulations 2007 make it clear that information concerning significant residual risks and details of any critical design issues should be passed to others who may need it to construct, use, maintain or de-construct a structure or facility being designed. The risk register is generic for this project. It will need to be refined and developed for each element of works completed at the site.

The initial risk refers to the perceived risk before the implementation of control measures. The residual risk refers to that after implementation of risk mitigation measures. The risks are for isolated solutions, and should be considered on the basis of all things being equal. Combinations of the various solutions may be required.


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8 REFERENCES

1 Michael D. Joyce Associates “A45(T) Weedon, Flore and Upper Heyford Bypass – Site Investigation Report”, December 1990. HAGDMS Report No. 10009. Document reference No. 446B.

2 British Standard EN 1997-2:2007 “Eurocode 7 - Geotechnical Design. Ground Investigation and

Testing”. UK.

3 Michael D. Joyce Associates ”A45(T) Weedon, Flore and Upper Heyford Bypass – Desk Study

Report”, December 1990. HAGDMS Report No. 10009. Document reference No. 446B.

4 WSPE “A45 Daventry Link Road – Preliminary Sources Study Report”, September 2013.

5 British Geological Survey Geological Map “Northampton - Sheet 185 (Solid and Drift Edition)”,

1:50,000 scale.

6 British Geological Survey Geological Map Sheet SP66SW (Solid Edition) 1:10,560 scale.

7 Brown, J., “Archaeological geophysical survey and trial trench evaluation of the A45

Northampton to Daventry Link Road, Northamptonshire, 2013-2014” MOLA Northampton,

report 14/5.

8 Geotechnics Limited Factual Report “Ground Investigation at A45 Daventry Link Road”,

February 2014.

9 Highways Agency “Interim Advice Note 73/06 – Design Guidance for Road Pavement

Foundation (Draft HD25)”, 2009. UK.

10 British Standard 1377-2:1990 “Soils for Civil Engineering Purposes – Classification Tests”. UK

11 British Standard 1377-3:1990 “Soils for Civil Engineering Purposes – Chemical and

Electrochemical Tests”. UK

12 British Standard 1377-4:1990 “Soils for Civil Engineering Purposes – Compaction Related

Tests”. UK

13 British Standard 1377-5:1990 “Soils for Civil Engineering Purposes – Compressibility,

Permeability and Durability Tests”. UK

14 British Standard 1377-6:1990 “Soils for Civil Engineering Purposes – Shear Strength Tests

(Total Stress)”. UK

15 British Standard 1377-7:1990 “Soils for Civil Engineering Purposes – Shear Strength Tests

(Effective Stress)”. UK

16 Stroud, M. A., “The Standard Penetration Test in Insensitive Clays and Soft Rocks,

Proceedings of the European Symposium on Penetration Testing” 1975.

17 Peck, R. B., Hanson, W. E. and Thornburn, T. H., “Foundation Engineering” 2nd Edition 1967.


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18 British Standard 8002:1994 “Code of Practice for Earth Retaining Structures”. UK

19 Skempton, A. W., Leadbetter, A. P. and Chandler, R. J. “The Mam Tor Landslide, North

Derbyshire” 1985.

20 CIRIA Report 143 “Standard Penetration Tests (SPT): Methods and Use” 1995.

21 Highways Agency Interim Advice Note 73/06 “Design Guidance for Road Pavement

Foundations” 2009.

22 Black, W. and Lister, N. W., “The Strength of Clay Fill Subgrades: Its Prediction and Relation to

Performance”. Institute of Civil Engineers 1978.

23 Manual of Contract Documents for Highways Works “Volume 1 Specification for Highways

Works - Series 600”, 2009.

24 CIRIA Report 181 “Piled Foundations in Weak Rock” 1999.


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Appendix A – Drawings and Figures

S397/036 Alignment Option 6 – Base Plan and Longitudinal Sections GEO-PC135450-001(1) Exploratory Hole Location Plan Figure 1 Geological Extract

See Sheet 1

See Sheet 2

Key

Borehole

CPT

Soakaway Trial Pit

Trial Pit

TRRL

Water Sam

ple

Surface Water Level

Y:\#Soil And G

roundwater\D

ELTEK Projects\00

03

98

80

- A45

Daventry Link R

oad - Flore Weed

on\(09

) Draw

ings\Geo B

H Location Plan\G

eo-PC135450-0

01.dw

gD

yke, Jack

Meters

0150

300

A45 Daventry Link RoadGround Investigation Report

39880April 2013

C12/013-CCSL British Geological Survey. ©NERC. All rights reserved

FIGURE 1Extract from BGS Geological Map Sheet 185


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Appendix B – Geotechnics Ltd. Factual Report

Geotechnics Ltd. Factual Report “Ground Investigation at A45 Daventry Link Road” February 2014.