Three Axis Experimental Study On Unsaturated Soil Of Old Clay In Changchun

At present,the study of unsaturated soils is a hot topic in geotechnical engineering,and this research focuses on two aspects:Theory and experiment.Compared with saturated soil,there is a four phase system in unsaturated soil,in which the existence of gas phase makes it very complex,which brings many engineering problems to the design and construction of geotechnical engineering.At present,some engineering problems of unsaturated soils are still being solved by the theory and method of saturated soil,which will inevitably bring about impacts on engineering design and construction.Due to the lack of advanced instruments and the lack of theoretical and Experimental Research on unsaturated soils in Changchun,this study aims to provide important technical parameters for geotechnical engineering investigation,design and construction in Changchun.For this reason,the conventional three axis consolidation and drainage test,the water soil characteristic curve test and the three axis consolidation and drainage test of unsaturated soil are carried out for the old clay original soil samples in Changchun area.The properties of unsaturated soils are analyzed by comparing the results of the three axis and unsaturated soil three axis tests.Research shows:When the matric suction is zero,the shear strength index of unsaturated soil is basically the same as that of the conventional three axis test.The increase of the matrix suction does not affect the change of the effective internal friction angle,which is basically equal to the effective internal friction angle obtained by the conventional three axis,but has a great influence on the cohesive force.When the matrix suction((u_a-u_w)?100kPa),Cohesion and matric suction are nonlinear growth relations,and the growth curve gradually slows down;When the matrix suction(u_a-u_w)(29)100kaP,Cohesion has a linear growth relationship with matric suction;The parameter?brelated to matric suction is not a constant,When(u_a-u_w)?100kPa,?bdecreasing with the increase of matric suction;When(ua-uw)(29)100kPa,?b tending to be stable,Its value?b(28)28.81?.The results are consistent with the Fredlund shear strength correction theory.On this basis,the stability of soil slope in saturated and unsaturated soils is simulated by ABAQUS numerical simulation software,and the stability safety factor of saturated and unsaturated soil slopes is obtained.Through comparison,it is concluded that the matrix suction has a great influence on the shear strength of unsaturated soils.With the increase of matrix suction,the safety factor increases and the depth of the sliding surface deepens.