BASEMENT DEWATERING IN GREATER LONDON
CHELSEA
Introduction:
THis project involves a basement excavation for a housing development in London. The project includes underpinning and has encountered shallow groundwater during excavations.
The works:
To address the groundwater issue, PDL designed and implemented a solution consisting of four deepwells strategically placed within the basement footprint. These deepwells extend to a depth of 6m below the existing ground level and penetrate through sands and gravels to reach the underlying clay. Despite the tight site having limited access, a cutdown cable percussion drill was utilized to drill the deepwells effectively.
MOLESEY
Introduction:
The project involved the excavation of a new proposed basement as part of the redevelopment of a domestic property. The project encountered delays due to rapid groundwater ingress. Project Dewatering worked to overcome significant risks and challenges to provide the client with a dewatering system.
The works:
The company employed specialized drillers and a cutdown rig to drill six deepwells around the basement footprint. The wells were drilled to a depth of 10m, utilizing a bore size of 250mm and an internal diameter of 126mm. The wells were cased with 1mm slot pipe and surrounded by 2mm to 4mm filter sands. The dewatering system successfully produced clean water, allowing for safe and dry excavation conditions.
WANDSWORTH
Introduction:
This project involves the extension of an existing basement. The 70m perimeter basement extends to 4.5mbgl. The site investigation report indicated the presence of made ground over gravelly clayey sands (Lynch Hill Gravel Member), and groundwater levels were encountered at 2.7mbgl.
The works:
To facilitate the extension of the basement, PDL proposed a deepwell dewatering system consisting of five deepwells. This approach was chosen due to its practicality, requiring less space compared to a full perimeter wellpoint system. The deepwells were strategically placed, with two wells located in the front garden extending to a depth of 8m and three wells internal to the excavation footprint reaching 5mbgl. This system effectively manages groundwater levels, allowing for the safe progress of the basement extension
