Project Overview
WHL Engineering was instructed to undertake a targeted structural survey at a multi-building school site following a fuel oil spill that required removal of contaminated soil near one of the main buildings.
Concerns were raised that excavation works could undermine shallow foundations due to the sloping site and clay subsoil conditions. The inspection focused on assessing foundation depths, ground levels, and structural risks associated with soil removal, as well as reviewing surface water drainage arrangements adjacent to the affected building.
The inspected building comprises sections constructed at different periods, with stepped foundations responding to the site’s natural slope. The underlying soil is predominantly soft to medium clay. Excavation to remove contaminated material had reduced ground levels locally; however, foundation depths were confirmed to remain below the reduced levels, indicating that the structures were not at immediate risk of undermining. A compromised foundation was identified at one corner of the original building, requiring localised structural support. In addition, surface water management was found to be inadequate, with a partial French drain terminating prematurely, increasing the risk of water retention within the clay strata and potential localised flooding.
It was recommended that a new pad foundation be installed at the affected corner to provide adequate support to the masonry wall. Soil excavation works could proceed elsewhere without compromising existing foundations, provided current levels were maintained. To address long-term moisture risks, a continuous French or land drain should be installed around the building perimeter and connected to a suitable outfall, improving groundwater management and reducing the likelihood of water accumulation adjacent to the foundations.
Whether you need structural design, an appraisal of an existing building, investigation of a structural issue or civil engineering support for a development, speak to WHL Engineering about the right way forward.
