DEWATERING OF FOUNDATION

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Diaphragm Wall Construction

Long sections of the cut and cover use diaphragm walls to support the sides of the open excavation, while work on the relocation of services and the construction of the in situ horse-shoe tunnels takes place. Once cast and set, the Tunnels are completely self-supporting and are not dependent on the diaphragm walls for structural stability.

The equipment used for excavation of diaphragm wall

This type of wall, known in North America as "slurry trench", is a cutoff wall made of a mixture of bentonite (weathering of volcanic ash ) and aggregates. A fairly wide trench (commonly 5 ft) is excavated under bentonite slurry.Excavated materials (aggregates) are placed in the trench in such a way that the backfilled aggregates form a gentle slope in the opposite direction from ongoing excavation.To ensure an effective cut-off effect, slurry trenches must be rather wide so as to compensate the possible defects due to the simple dumping procedure.

Construction sequence of a slurry trench

Contiguous/Secant pilling

ˈˈ Rock foundation treatment for damsˈˈ Rock cutoff curtainsˈˈ Pressure injected anchorsˈˈ Ground treatment for tunneling applicationsˈˈ Void filling in mines

TEMPORARY METHODS OF DEWATERING