Study On Permeability Of Soft Soil In Hangzhou Area

Soft soil is a special soil which is formed in the static water environment.It's widely distributed in the coastal and inland areas of china.Due to the environment and conditions are different,the distribution,composition,structure,physical and mechanical characteristics of soft soil in different regions are obviously different.The study of the characteristics of regional soft soil is of great significance to the construction of the project.In this paper,the permeability of soft soil in Hangzhou area is analyzed and studied by laboratory test,and analysis of a foundation pit in Hangzhou.The main conclusions are as follows:(1)In this test,ten groups of samples of clayey soil and sandy soil were set up.The physical and mechanical properties were studied by means of basic soil tests.Proposed the void ratio increases with the increase of water content,and decreases with the increase of the density,and have a good linear relationship.According to fit the data of geological investigation report of Hangzhou soft soil.The relationship between void ratio and water content and gravity is obtained,the relationships are e=0.0277w+0.024?e=-0.2295?+5.2069.That can estimate the porosity ratio of soil in Hangzhou area.Density is affected by water content and saturation,when the soil saturation is low,the density increases with the increase of water content,when the saturation is close to saturation,the density decreases with the increase of water content.(2)The permeation of specimens was studied by using GDS test system.The results show that: the void ratio decreases nonlinearly with the increase of consolidation pressure.With the increase of consolidation pressure,the void ratio change of cohesive soil is larger than sandy soil,and the nonlinearity is more obvious;The larger non-uniformity coefficient of sandy soil,the larger granularity distribution range,the more uneven soil,the smaller pore,so that the flow channel in soil reduce or extend,and soil permeability decreased;The greater plasticity index of clay soil,the more combined water,the thicker water film around soil particles,the smaller the pore size of soil particles,the weaker soil permeability;The permeability coefficient decreases with the decrease of the void ratio.There is a linear relationship between permeability coefficient and void ratio,but the permeability coefficient and void ratio of clay soil are nonlinear.The change of void ratio has a greater influence on clay soil.(3)The nonlinear permeability characteristics of cohesive soil samples are studied by four nonlinear permeability models.The parameters of lg[k_v(1+e)]-lge,e-lgk_v,lgk_v-lge,lgk_v-lg(1+e)are obtained.The cohesive soil samples have good applicability to lg[k_v(1+e)]-lge and lgk_v-lge models.(4)The dewatering in foundation pit will cause the seepage,and change the physical and mechanical properties of the soil around the foundation pit,which will affect the foundation pit.Through the analysis of the precipitation data of a deep and big foundation pit in hangzhou,and considering the effect of sealing structure,a calculation method for the maximum drawdown of groundwater level outside the semi closed foundation pit with homogeneous aquifer is proposed.In soft soil area,during the dewatering in foundation pit,the seepage of groundwater forms a drawdown cone around the foundation pit.Groundwater level outside the pit will be reduced,the soil consolidation and ground subsidence.The groundwater level outside pit has a linear relationship with the ground subsidence.Dewatering can improve the physical and mechanical properties of soil at the bottom which is equivalent to reinforcement.It can inhibit the bottom rebound and make the upright post sinking.The shear strength and soil self-standing of the soil outside pit is improved,reducing the pressure acting on the enclosure structure.It helps the stability of foundation pit.The results obtained in this paper can provide reference for similar engineering.