Central Alliance Delivers Ground Investigation Solution for Proposed A628 Drainage System
The A628 is a major road in the north of England connecting Greater Manchester and South Yorkshire by crossing the Pennine chain of hills by way of the Woodhead Pass through the Peak District National Park.
The road’s altitude and its exposure to bad weather create problems in winter and the road is sometimes closed due to snow or high winds. As part the A628’s on-going maintenance, it is proposed to install significant new drainage systems into the existing eastbound cut slope at Longside, a busy stretch of the road that traverses the Pennines. Specifically, works will result in a steepened slope, which will need to be stabilised. In order for the appropriate drainage solution to be designed, Highways England needed to understand ground conditions and therefore required a Ground Investigation solution, which would provide data such as material parameters for the design of the reprofiled cutting slope and stabilisation measures. In addition, the GI would establish the ground and groundwater conditions of the eastbound cutting slope.
Central Alliance was awarded the contract to provide the Ground Investigation works for the project, which involved the mobilisation of its in-house specialist slope access rotary coring and dynamic sampling rigs, simultaneously at multiple borehole locations at the toe, crest and mid-slope of the embankment.
The project was not without its challenges; detailed planning and logistics were required due to small site access and the need for multiple rigs to work simultaneously. In addition, Central Alliance had also to continually report, update and communicate with A-one+, the Main Contractor, to ensure it met the working time restrictions. There were also the challenging technical requirements of works, such as having to deal with slopes that are notoriously difficult to work on. A single lane carriageway, and as one of the main transport links across the Pennine, access times were also understandably restricted, requiring rigs to be mobilised and removed within a 6-hour window.
As a result, it was essential to implement a programme of thorough planning, communication and working with the Client to ensure that full utilisation of the time available was exploited and to provide the necessary data to inform the Designers within the available short working windows.
The site was split into 7 sections along the 1.5km section of the slopes, with each section being completed in order, requiring multiple rigs to work simultaneously. Again, planning and site layout of equipment, tooling, and rig access was essential to ensure efficient mobilisation, on-site activity and moreover the preservation of safety and welfare of operational staff.
Central Alliance’s Ground Investigation Solution comprised:
- 10No. dynamic sample boreholes with rotary cored follow-on located on the eastbound cutting slope and verge
- 9No. dynamic sample holes located on the eastbound cutting slope and verge using MIP-18 slope climbing rig
- In-situ testing comprising hand shear vanes and SPTs
- Instrumentation and monitoring
- Geotechnical laboratory testing
- Geoenvironmental testing
- Provision of data in AGS format and factual reporting
Work commenced in August 2018 and was completed on-time and to budget, and sees Central alliance extend its already dominant position working on TransPennine on Rail, to the many highway routes across the Pennine regions.