A46 Coopers Hill & Green Street, Gloucestershire - Ground Investigation

Gloucestershire County Council alongside their contractor AtkinsRéalis require a contractor to undertake a ground investigation to assess ongoing slope movement of Coopers Hill, which impacts two areas of the A46 carriageway and associated piled retaining wall, located near Brockworth. The damage relates to ongoing regional slope movement that extends above and below the A46 carriageway. A ground investigation is required to characterise the ground conditions under two sites. The investigation will also install monitoring equipment to monitor ongoing ground movements and groundwater levels to identify the failure mechanism.

The ground investigation will comprise an intrusive investigation to characterise the ground conditions. Prior to intrusive works, it is imperative that the risk from buried services and overhead cables has been mitigated through, but not limited to, ascertaining the location of the services at the site, by use of cable avoidance equipment, risk assessments and any other means to mitigate potential risks. This will then inform the locations of the intrusive holes. The intrusive activities comprise:

Eight (8 No.) boreholes commencing with dynamic sampling followed by rotary coring to between 20-50m bgl, including the following instrumentation;

Three (3 No.) inclinometers to monitor ground movements;

Four (4 No.) 50mm standpipes to monitor groundwater levels.

Geotechnical sampling, in-situ and laboratory testing, and the production of a factual report, with associated AGS file, will be required.

Surveying of grid coordinates and ground levels of each of the exploratory holes to Ordnance Survey grid and datum, including the corners of service inspection pits will be required.

The works will be organised and managed by the Principal Contractor. The Principal Contractor shall appoint a trained and competent person/organisation to undertake TM design and implementation throughout the works, a detailed TM plan for review shall be issued to the Principal Designer within one week of the preferred Principal Contractor being notified of contract award. One week is required for review, and actions arising from the review will be communicated to the Contractor via the Principal Designer, it is expected that these actions (or agreed alternative action) will form part of the final TM plan. If a detailed TM plan for review has not been provided within one week of the preferred Principal Contractor being notified of contract award, the Client reserves the right to appoint an alternative Principal Contractor.

A single lane closure, operated under 2-way traffic signals, to be utilised for the works at the Green Street site and for access and storage for works below the Piled Retaining Wall. The works are planned to take place between 7th May and 4th July 2024.

It is anticipated that two rigs (2 No.) will be required to complete the work in the proposed timescale of 4 No. weeks with 2 No. Engineers.