A residential care home together with associated car parking, gardens and soft landscaping was required in Edinburgh. In order to construct the care home, a retaining wall up to 5m high was required, surrounding the northern perimeter of the development.
With existing water table levels above the proposed excavation formation, a temporary dewatering system was required to reach formation level. Following excavation to formation level, a permanent groundwater control system was required to maintain water levels across the development below ground level.
OGI was engaged to provide a preliminary design of the temporary and permanent groundwater control systems, to quantify potential seepage volumes through the retaining wall and to ascertain potential settlements under surrounding properties due to lowering the water table.
The final dewatering design comprised dewatering wells, installed at 4m centres around the inside of the contiguous pile wall, to a level of 41.4m OD and connected to a vacuum suction pumping system.
To provide permanent works pressure relief within the building footprint and behind the contiguous pile retaining wall, a system of wick drains was installed between individual piles, tied into a drainage layer below and around the building which leads to a passive drainage system.