Our projects

Supporting tank installation in difficult ground conditions

Horsey, Somerset

A tank installation at the Sydenham Farm development in Horsey, near Somerset was quite the challenge with bad ground providing an obstacle for developers. We were contacted by subcontractor Highfield Tunnelling Ltd, acting on behalf of contractor John Sisk & Son Ltd, for our help on this six month-long project.

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90

M12 Overlapping Trench Sheets used to combat the high water table

2

Levels of Super Shaftbrace used to support the excavation

12m

long tanks installed

Overview

Early testing identified the site having difficult ground conditions and a high water table
We engineered a sheet & bracing frame solution to combat the issues
Installation of 4x 12m long tanks

Products used on this project

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.

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