Study On The Strength Characteritics Of Unsaturated Cohesive Soil With Different Initial Dry Density

The most area of earth's surface environment(except for the sea area)is arid or semi-arid where the majority of soils are mostly unsaturated.With the development of theoretical research on geotechnical mechanics,technology and the demand of unsaturated soil theory in practical engineering,the study of unsaturated soil has become a hotspot issues for the geotechnical scholars at home and abroad.At present,there are many of unsaturated soil,and the definition of characteristic parameters in those strength theories are also different.In the selection of unsaturated strength formula and parameters,there is no uniform standard.Therefore,the research on the strength characteristics of unsaturated soils have great significant meaning.Based on the strength classical theory of unsaturated soil,this paper presents a soil-water characteristic curve(SWCC)experiment,a triaxial test of saturated soil and a triaxial test of unsaturated soil under the condition of different initial dry density,the corresponding studied object is Wuhan unsaturated cohesive soil.According to the analysis of experimental data,the applicability of classical strength formula of unsaturated soil and the variation law of strength parameters of Wuhan unsaturated cohesive soil have been studied during a year and a half.And the conclusions are as follows:(1)According to pressure plate test,the characteristics SWCC of Wuhan unsaturated cohesive soil have been researched.Test shows that the initial dry density has great influence on the initial water content of soil sample and the amount of large diameter pores,but has little influence on small diameter pores.During the drying process,at the stage of low suction,the rate of water loss and the water content of sample whose dry density is large are smaller than those of sample whose dry density is small.When the suction value increases gradually,the rate of water loss of different dry density is coincident,moreover,the difference of water content is reduced.(2)The SWCC test data are fitted and analyzed by using model,then this paper find that the air-entry values of sample of different initial dry density are positively correlated with the dry density,while the residual water content has no significant correlation with the dry density.(3)this paper carries out the triaxial tests of unsaturated soil under the different test environment,the test results show that the failure of soil is shear dilation,the deformation shows obvious "drum" shape and is greatly effected by the dry density and the matrix suction.The stress-strain curve is characterized by stress-hardening type and no an obvious peak value.And 15% stress peak value is positively correlated with the dry density,net confining pressure and matrix suction.(4)According to the treatment of the experimental data,it is found that the strength parameterb? is negatively correlated with the matrix suction and net confining pressure.Its value is affected by the dry density,but there is no obvious correlation.(5)According to the study on the effective stress parameters ?,it is found that the parameters can be used to evaluate the relative degree of the effect of the net normal pressure and the matrix suction on the strength.And its predictied value is positively correlated with the dry density,while the measured value is negatively correlated with the net confining pressure and affected by the dry density and matrix suction but no obvious correlation.(6)For the two different prediction methods and formulas,combined with the experimental data,by comparing the predicted values and measured values under different conditions,this paper gives the qualitative analysis and the corresponding methods and formulas for the strength prediction of Wuhan unsaturated cohesive soil are given.