The challenge
Borehole tests on the ground showed it was made entirely of silt and sand, which along with a high water table would require extra attention and monitoring during the whole project.
Tight trench sheeting was essential on this project and our M12 Overlapping Trench Sheets were the perfect option to combat this problem. With the difficult ground conditions on this site, it was essential that the lapped sheets were installed accurately, ensuring a good bite on the lap to prevent the ingress of fines with any groundwater. With the groundwater level at -2600mm in the 3400mm deep excavation, base stability problems were still possible.
Our solution
Ninety M12 Overlapping Trench Sheets were driven into the ground first, with Mabey Hire engineers identifying the push and dig method as the best option. The trench sheets were pushed into the ground with the toe-in depth of 3.4m required to combat the ground conditions.
Excavations with the 45 tonne plant then began, first digging to 1m below the surface, allowing the first Super Shaftbrace to be installed at 0.75m and pressurised. Excavations then continued down to 2.75m below the ground where the second frame could be installed and pressurised at 2.5m.
