Deep Well Dewatering - Ashby Folville Manor

Deep well dewatering to enable the construction of a residential basement

Project Overview

A comprehensive dewatering system was installed to allow the safe construction of a basement. 14no x 12m deep actively pumped pressure relief wells were installed using cable percussion drilling techniques at equidistant centres around the external perimeter of the basement.

To speed up the drawdown process and observe groundwater levels directly beneath the basement, 2no x 7m deep internal wells were installed from the lower basement slab level. Submersible borehole pumps pumped the groundwater through a settlement tank with final discharge into the adjacent brook.

Basement Detail

• Dimensions: 47.0m x 18.2m
• Excavation Depth: 5.20m below surface
• Excavation support: Secant piled wall

Objective

During the construction of a basement, Stuart Wells was contacted by the client who had stopped construction due to groundwater seepage. They needed a solution that would protect the basement from potential uplift and structural damage during construction.

Solution

A groundwater control system was implemented to reduce and control groundwater pressures below the deepest basement excavation level allowing works to proceed in safe and dry conditions.

Scope of Works

14no. x 12m deep external pressure relief wells were installed using cable percussion drilling techniques, evenly spaced around the basement perimeter. The wells penetrated the pressurised limestone beds allowing groundwater pressured to be controlled. To speed up the drawdown process and observe groundwater levels directly beneath the basement, 2no. x 7m deep internal wells were installed from the lower basement slab level.

Submersible 415v x 0.75kW borehole pumps were installed at the base of each well and controlled by water level sensor probes. Pumped groundwater was collected in a perimeter header main, passing through a settlement tank with final discharge into the adjacent brook.