THE LATERAL PRESSURE OF WET CONCRETE IN DIAPHRAGM WALL PANELS CAST UNDER BENTONITE.

Abstract

The lateral pressure exerted by wet concrete in diaphragm wall panels cast under bentonite is examined in the light of current methods of predicting concrete pressures on formwork. This leads to a prediction of critical depth, above which the full fluid concrete pressures apply, and below which pressures increase with depth following the slope of the bentonite line. A new case record of wet concrete pressures is presented for a diaphragm wall in Cambridge, and two previous case records are reviewed. All three sites clearly demonstrate the existence of a critical depth, and the data fit within the predicted bilinear envelope of maximum concrete pressure. Current methods give a reasonable prediction of the magnitude of the critical depth for walls up to 20m deep, but probably under-predict for deeper walls. It is suggested that wet concrete pressure diagrams adopted in analyses of wall installation effects should use the bilinear shape, with a critical depth at one-third of the wall depth. Concrete placing temperature appears to be a major factor in the development of wet concrete pressures, and may affect horizontal stresses at the end of wall installation. © 1994, Thomas Telford and ICE. All rights reserved.