Numerical modelling of installation effects for diaphragm walls in sand

The scope of this work is to study the mechanisms of load transfer and the deformations of the ground during slurry trenching and concreting in dry sand and to evaluate their effects on service structural loads, wall deflections and ground displacements behind the wall caused by subsequent excavation. A series of threedimensional finite element analyses were carried out modelling the installation of diaphragm walls consisting of panels of different length. The soil was modelled as either linear elastic perfectly plastic or incrementally non linear hypoplastic with elastic strain range. Plain strain analyses of diaphragm walls of identical cross section were also carried out in which wall installation was either modelled or the wall was wished in place. The analyses predict ground movements consistent with the experimental observations both in magnitude and trend. The results also show that maximum horizontal wall deflections and structural loads reduce with increasing panel aspect ratio towards a minimum which is about twice the value computed for wished in place analyses. Panel aspect ratios should be larger than about three to take advantage of three-dimensional effects. The pattern and magnitude of surface vertical displacements obtained from linear elastic perfectly plastic analyses, no matter whether three- or two-dimensional, are unrealistic.