Effect of concreting pressure on ground response caused by installation of diaphragm wall panels

The ground response during diaphragm wall panel installation is strongly affected by the support slurry pressure, and by the subsequent lateral pressures during the tremie placement and set-up of wet concrete. The support slurry pressure can be reliably assumed as hydrostatic within the excavated trench, whereas the lateral concreting pressure is much more complex due to the stiffening effect of wet concrete. This paper reviews the measurements of wet concrete pressures from a series of instrumented diaphragm wall panels which show that lateral pressures in the concrete slurry increase as the tremie displaces bentonite slurry and reach a maximum condition about 1 h after placement, while conditions over the longer term closely approximate the hydrostatic pressure of the bentonite-filled trench. The maximum increase of pressure varies at different heights of the same trench, and also varies for two separate panels in the same project, reflecting the varying velocity of concreting. Model tests of concreting pressure on formwork also demonstrate that the lateral pressure reduces from hydrostatic wet concrete pressure a few hours after casting. A time-dependent lateral concreting pressure model is developed to represent these measurements more realistically. This proposed model is implemented into a finite-element program to investigate its effects on the ground response due to the concreting process. Computed results from a reference case can capture the progressive variations of ground movement, earth and pore water pressure in the soil adjacent to the trench during and shortly after the concreting process, which is consistent with the reported measurements.