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Excavation Box Leak Sealing

In November 2013, Soil Engineering were asked to produce a solution to ensure the watertightness of a sheet piled cofferdam in East London.

Due to the constraints of a Section 61 Notice, the Sheet Piles could not be driven through granular strata using a hammer, and were vibrated into place. Several piles failed to fully penetrate very dense River Terrace Deposits and seal into the London Clay below. The resulting gaps had to be “plugged” in order to ensure the safety of operations within the cofferdam, and to prevent free running material flowing into the excavation.

Soil Engineering designed a solution utilising pressurized microfine cementitious grout to both densify and consolidate the Terrace Gravel material. The Microfine Cement allowed the grout to permeate more effectively at low pressure further than OPC based Grout, ensuring that the grout could form an extended envelope beyond the area of densification, providing a seal across the gaps in the sheet piles. Grout was also injected into the upper 1m of the underlying London Clay, to ensure the seal tied into the fissured clay, and shut off the water pathway.

On acceptance of SEGL’s design by the client, the site crew were able to mobilise a Soilmech SM-8 drilling Rig, and Bauer hydraulic colloidal mixer/pump assembly in 1 week, to undertake the works under the supervision of a Soil Engineering Senior Engineering Geologist.

• Soil Engineering were able to work with the Client’s engineers to produce not only a solution which was cost effective and efficient to install, but a programme of works which had minimal impact on other works ongoing on the very tight site
• The grout design was derived to produce a highly penetrative and rapid setting grout which would allow the ground to be both stabilized and decreased in permeability in a short space of time, cutting impact on key site activities, and allowing excavation works to proceed without significant delay.
• The works were completed in less than 2 weeks utilising in house drilling plant and resources