Four retail units were to be constructed on this difficult site as the area had been backfilled with Pulverised Fuel Ash (PFA) in the past and this extended to a depth of some 20 metres. Unfortunately, the water table was very high and only 1 metre below ground level which resulted in a very soft PFA material below that depth.
Rather than opting for a piled foundation, we investigated in the use of a Tensar plastic membrane within a 600mm stone subbase utilising the Tensar in both the top and bottom areas of the stone fill. This reinforced stone backfill was utilised across the entire area of the site and even beneath the roads and services to ensure that any settlement was kept to a minimum and would also be uniform across the site area. This subsequently saved some £1m pounds in terms of the development cost.