A Study On Spheric Cavity Expansion And Static Piling In Soils

Spheric cavity expansion, static piling in subsoils and its application have been studied in this paper.Soil is assumed to be a homogeneous, isotropic and elastic-perfectly plastic material, and a dilational angle is used to consider soil dilatancy. By using the principle of the elasto-plastic theory, the analytical solution of the spherical cavity expansion including the ultimate pressure, the stress field and displacement field, plastic scope, the total volumetric increase, plastic and elastic volumetric increase was obtained. The effect of flow rule, the variations of the soil parameters and the drainage conditions of subsoils on the calculated results have been discussed and several conclusions are presented.On the study of the mechanism of static piling, a model of spherical cavity expansion at the pile toe while piling is introduced. The problem of static piling in half-space medium has been creatively solved by a source-source imaging technique and Boussinesq's solution. The solutions of a stress field, a displacement field, a pore pressure field and the variation of soil strength for pile installing have also been proposed. The resistance, displacement field, variation of soil strength caused by pile installation and the end bearing of static sounding have been calculated for six cases. It has been founded that the calculated results are approached to those of the observation in site.In practical application, the analytical solutions can be used to assess the resistance while piling and to select efficiently the piling equipment. Moreover, the formulas of calculating the "Critical Depth" and the "Minimal Thickness" are proposed. Several qualitative conclusions proposed by other scholars with in-site measurement results are theoretically confirmed. Three problems encountered in engineering have been solved: (1) the minimal thickness which the pile toe has to keep from the interface between the bearing stratum and the soft substratum; (2) the critical depth in which the pile toe thrusts in bearing stratum; (3) the variation of the critical depth and the minimal thickness for two different soil stratum. The critical depth and the minimal thickness determined by current pile code are compared with the presented results. A case of pile installation are analyzed, the effect of group piling on lateral displacement has been discussed and compared with in-site measurement results. Some suggestions have been proposed in this paper.