ANALYSIS OF SOIL COMPRESSION INDUCED BY PORE WATER PRESSURE DROP IN SOFT SOIL FOUNDATION

The compression modes of soil under pore water pressure drop are analyzed based on the basic principles of soil mechanics,and the layered settlements are investigated contrastively between theoretical calculation and field measurement in soft foundation improved with vacuum preloading.The unit compressions are analyzed quantitatively at different depths of soil and the following conclusions are drawn:(1) according to the analysis of the principle of effective stress,the soil pressure and the water pressure are calculated individually to arbitrary soil element,where the vertical total stress keeps constant and lateral total stress is reduced with the pore water pressure drop;(2) pore water pressure drop induces soil element isotropic compression in the range lower than local atmospheric pressure,and pore water pressure drop induces one-dimensional compression of soil element in the range greater than local atmospheric pressure;(3) the case study shows that calculated ground settlement by incomplete consolidation soil is consistent with the field measured settlement approximately in vacuum preloading project of Nansha Port,and the settlement induced by secondary consolidation of gravity is an important proportion of total ground settlement during the period of vacuum preloading;(4) the prefabricated vertical drains are installed deeper,and the improvement depth of vacuum preloading is greater,however,the effect of soil compression is smaller with depth increase in vacuum preloading project.The design of prefabricated vertical drains should consider the optimal improved depth when soft foundation is improved with the technique of pore water pressure drop.