This was a new building designed to store grain for long periods, that would impose heavy, sustained loads over a large area. The ground conditions comprised soft peaty, clayey silts to about 6m, graduating into sands and gravels.

The initial foundation design based on a standard site investigation offered a completely piled building, which would have made the project unviable. When the client approached us we undertook a detailed geotechnical analysis of the ground conditions including effective stress testing. This predicted that if a non-suspended floor slab was to be used there would be a high risk of catastrophic failure of the building by side squeezing owing to the build-up of excess pore pressures during filling; and that consolidation settlement at the centre of the slab would reach 450mm.

With the benefit of the detailed analysis we designed a solution using a floating flexible floor slab. A geotechnical monitoring system was designed and installed. This used hydraulic piezometers and a variety of settlement gauges. Harrison Geotechnical then took on the responsibility of controlling the grain filling operation by monitoring the pore pressure profiles. This exercise resulted in a grain store that was full and a structure that performed safely, and within the predicted movement tolerances. The client was pleased as the exercise resulted in a 90% reduction in the original foundation budget.