Lyon Way, Frimley Flood Alleviation Scheme

Clients: J Murphy & Sons and Thames Water

Duration: 12 weeks

Location: Lyon Way, Frimley

Description of works:

Michael Roarty, working for J Murphy & Sons completed a 15m diameter caisson concrete segmental shaft, 13.5m deep, at Lyon Way. The shaft included a 2m x 3m collar and a 3m deep plug, which formed part of the permanent works for anti-flotation.

A driven sheet piled wall was installed to allow excavation of the collar, without the requirement for secondary walling systems for either the excavation itself or to support the adjacent crane pads.

Two stage dewatering was required. The upper aquifer within the river terrace gravels deposits was dewatered using a conventional system with well-points installed within the pans of the sheet piles.

The lower level within the Camberley Sands Windlesham formations was dewatered using an ejector system, installed to 28m deep.

Dewatering was used in preference to sinking the shaft under wet conditions, to remove the risk of settlement to the adjacent rail lines or highway structures.

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