A428 Black Cat to Caxton Gibbet Improvements
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A428 Black Cat to Caxton Gibbet improvements TR010044 Volume 6 6.3 Environmental Statement Appendix 9.1: Ground Investigation Summary Report Planning Act 2008 Regulation 5(2)(a) Infrastructure Planning (Applications: Prescribed Forms and Procedure) Regulations 2009 26 February 2021 A428 Black Cat to Caxton Gibbet improvements Environmental Statement – Appendix 9.1 Ground Investigation Summary Report Infrastructure Planning Planning Act 2008 The Infrastructure Planning (Applications: Prescribed Forms and Procedure) Regulations 2009 A428 Black Cat to Caxton Gibbet improvements Development Consent Order 202[ ] Appendix 9.1: Ground Investigation Summary Report Regulation Reference: Regulation 5(2)(a) Planning Inspectorate Scheme TR010044 Reference Application Document Reference TR010044/APP/6.3) Author A428 Black Cat to Caxton Gibbet improvements Project Team, Highways England Version Date Status of Version Rev 1 26 February 2021 DCO Application Planning Inspectorate Scheme Ref: TR010044 Application Document Ref: TR010044/APP/6.3 A428 Black Cat to Caxton Gibbet improvements Environmental Statement – Appendix 9.1 Ground Investigation Summary Report Table of contents Chapter 1. Introduction 1 1.1 Introduction 1 1.2 Description of the Scheme 1 1.3 Overview of Scheme location 2 1.4 Details of the ground investigation 2 1.5 The results of the ground investigation 4 1.6 References 15 Annex A: Drawings 20 Table of Tables Table 1-1: Summary of Geology .......................................................................................... 5 Table 1-2 Historical land uses within the Geology Study Area (From Envirocheck Report) ........................................................................................................................................... 11 Table 1-3: Contemporary potentially contaminative land uses within the Order Limit ........ 16 Table 1-4: Soil contaminant testing results ........................................................................ 18 Planning Inspectorate Scheme Ref: TR010044 Application Document Ref: TR010044/APP/6.3 A428 Black Cat to Caxton Gibbet improvements Environmental Statement – Appendix 9.1 Ground Investigation Summary Report 1. Introduction 1.1 Introduction Due to the limited availability of existing geological and geotechnical data along the Scheme route and the need for a comprehensive ground investigation to inform the design of the Scheme was identified. The purpose of the ground investigation was to provide additional geological, geotechnical and hydrogeological information to facilitate the design and construction of the new road and associated earthworks and structures, including overbridges, underbridges, cuttings, culverts, footbridges and embankments. Appendix 9.1 provides a summary of the findings of the ground investigation completed on the Scheme between September 2019 and April 2020 and has been informed by the Ground Investigation Report (Ref 1-1) and findings of the Preliminary Sources Study Report (PSSR) (Ref 1-2). The appendix concentrates on the geological and ground contamination aspects of this reporting. 1.2 Description of the Scheme The A428 Black Cat to Caxton Gibbet Improvements Scheme (the Scheme) has been developed by Highways England to address problems of congestion, poor journey times and poor resilience against incidents between the existing Black Cat and Caxton Gibbet roundabouts. The Scheme proposes the construction of a new 16 kilometre (10 mile)) dual 2-lane carriageway from the Black Cat roundabout to Caxton Gibbet roundabout, to be known as the A421 (hereafter referred to as the ‘new dual carriageway’) and in addition approximately 3 kilometres (1.8 miles) of tie-in works. The Scheme includes the following components: a. A new three-level grade separated junction at Black Cat roundabout, with the A1 at the lower level, the new dual carriageway on the upper level and a roundabout between the two at approximately existing ground level. In addition to slip roads, a new free flowing link between the A421 eastbound carriageway and the A1 northbound carriageway will also be provided. b. A new grade separated all movements junction will be constructed to the east of the existing Cambridge Road roundabout to provide access to the new dual carriageway and maintain access to the existing A428. c. At the Caxton Gibbet roundabout, a new grade separated all movements junction will be constructed, incorporating the existing roundabout on the south side of the new dual carriageway and a new roundabout on the north side. The new dual carriageway will then tie-in to the existing A428 dual carriageway to the east of the new Caxton Gibbet junction. Planning Inspectorate Scheme Ref: TR010044 1 Application Document Ref: TR010044/APP/6.3 A428 Black Cat to Caxton Gibbet improvements Environmental Statement – Appendix 9.1 Ground Investigation Summary Report d. In the vicinity of the new Black Cat junction, direct access onto the A1 from some local side roads and private premises will be closed for safety reasons. A new local road will provide an alternative Scheme route. The existing Roxton Road bridge will be demolished and replaced with a new structure to the west to accommodate the realigned A421. e. New crossings will be constructed to enable the new dual carriageway to cross the River Great Ouse, East Coast Main Line railway, Barford Road, the B1046/Potton Road, Toseland Road and the existing A428 at Eltisley. f. The existing A428 between St Neots and Caxton Gibbet will be de-trunked and retained for local traffic and public transport with maintenance responsibility transferred to the local highway authorities. g. An alternative access will be provided to side roads at Chawston, Wyboston and Eltisley. h. There will be safer Scheme routes for walkers, cyclists, and horse riders. A detailed description of the Scheme is set out in Chapter 2, The Scheme of the Environmental Statement [TR010044/APP/6.1]. 1.3 Overview of Scheme location From the existing Black Cat Roundabout to the East Coast Main Line the area is characterised by the low-lying floodplain of the River Great Ouse, which is dissected by drainage ditches and hedgerows, with an elevation of approximately 17m AOD (Metres Above Ordnance Datum), rising to a maximum of around 25m AOD at Barford Road. From the East Coast Main Line railway moving north easterly through undulating open fields the ground level rises to around 50m AOD before dropping to approximately 20m AOD at Hen Brook. At the Cambridge Road junction, the Scheme route is at a level of approximately 35m AOD. Progressing east the land is less undulating and gradually rises to an elevation of around 66m AOD at the Caxton Gibbet junction at the eastern end of the Scheme. The Scheme route passes through predominantly undulating agricultural land, with embankments along the Scheme route up to 9.5m high and cuttings up to 8m deep. The Scheme route will also include the construction of 55 structures (culverts) over watercourses across the Scheme 1.4 Details of the ground investigation A review of the existing geological, hydrogeological and geotechnical information for the Scheme route, contained in the Preliminary Sources Study Report (PSSR) (Ref 1-2), identified the shortage of suitable ground conditions information for large sections of the Scheme route. Information was predominantly available from previous shallow investigations at the existing Black Cat and Caxton Gibbet roundabouts. The PSSR (Ref 1-2) identified the need for a full intrusive ground investigation along the Scheme route to enable a detailed geotechnical design to be undertaken. Planning Inspectorate Scheme Ref: TR010044 2 Application Document Ref: TR010044/APP/6.3 A428 Black Cat to Caxton Gibbet improvements Environmental Statement – Appendix 9.1 Ground Investigation Summary Report The fieldwork comprised of the following activities: a. 83 no. Boreholes constructed using Cable Percussion rigs to depths between 2.9m and 30.45m. b. 195 no. Trial pits excavated to depths between 0.8m and 4.3m. c. 102 no. Windowless sample (WS) boreholes to depths between 1.0m and 10.45m. d. 76 no. TRL Dynamic Penetrometer test holes to a maximum depth of 2.22m e. 7 no. packer tests. f. 3 no. Falling head tests. g. Groundwater monitoring installations. h. In-situ testing comprising standard penetration tests, hand penetrometer tests and hand shear vane tests. i. Sampling and laboratory analysis for geotechnical and geo-environmental purposes. The exploratory hole logs are included in the Factual Report. Laboratory testing of representative samples of the materials recovered from the exploratory holes was carried out to enable the determination of characteristic soil parameters for use in the design of the geotechnical elements of the Scheme. Geotechnical laboratory testing was carried out on representative samples of the soils recovered from the exploratory holes. Geotechnical laboratory testing comprised the following tests: a. 521 no. Water Content tests. b. 345 no. Atterberg Limit Determinations. c. 155 no. Particle Size Distribution tests by wet sieving. d. 118 no. Particle Size Distribution tests by hydrometer/pipette. e. 97 no. Unconsolidated undrained single stage triaxial compression tests. f. 4 no. Consolidated undrained single stage triaxial compression tests. g. 15 no. Consolidated undrained multistage triaxial compression tests. h. 39 no. One-dimensional consolidation tests. i. 31 no. Compaction Tests using 4.5kg rammer. j. 4 no. Compaction Tests using vibrating rammer. k. 27 no. Moisture