Experimental study on permeability properties of soft clay in process of pumping and recharge

For controlling the settlement caused by dewatering of deep foundation pits, the method of recharging is usually adopted. But the permeability coefficient of soft clay may change along with the variation of void ratio during the pumping and recharge, and it will affect the results of recharging and deformation characteristics of soils. For studying the permeability characteristics of Shanghai typical soft clay under the effect of pumping and recharge, the pumping and recharge tests were carried out on the soft clay by using the GDS triaxial apparatus. During the tests, the soil stress level is controlled by setting the radial pressure and initial pore pressure. Meanwhile, the process of pumping and recharge is simulated by changing the back pressure. The void ratio and permeability coefficient are obtained by dealing with the experimental results and data. The study shows that the permeability coefficient has a nonlinear relationship and a decreasing trend along with the decrease of void ratio during the pumping. During the recharge, with the increase in void ratio, the permeability coefficient has a decreasing trend due to the blockage effect and is smaller than that at the pumping stage. Meanwhile, the nonlinear relationship between permeability coefficient and void ratio can be fitted using the function of e-lgk.