Study Of Moisturizing Deformation Properties Of Unsaturated Collapsible Loess

Loess,as a kind of special soil with water sensitivity,is widely distributed in the world.Its water sensitivity is mainly manifested by the influence of moisture contents on the physical and mechanical properties,such as deformation,strength and constitutive relationship.In fact,the problem of collapsibility has been an interesting research topic in loess mechanics and engineering.Loess is mostly distributed in arid and semi-arid areas and exists in an unsaturated state.Therefore,the study of unsaturated loess deformation characteristics is of great significance for solving practical engineering problems.Taking the unsaturated collapsible loess in Qilihe area,Lanzhou city,Gansu province as research object,the moisturizing deformation characteristics of unsaturated loess were studied by the combination of experimental and theoretical analysis.The main research contents of this article are as following:1.The basic physical and mechanical parameters of the undisturbed unsaturated loess from Qilihe district,Lanzhou city were yield by laboratory experiments.That mainly includes the initial water content,liquid plastic limit,density,maximum dry density and optimal water content,etc.2.The shear tests for unsaturated soil by direct shear apparatus.the tests process include control different matric suction of unsaturated soil direct shear test and different moisture content of the conventional direct shear test,the strength of the sample parameters,combined with Lu based on absorption strength formula of the stress curve,draw the relationship between the stress and the effective absorption saturation curve.The relation curve between absorptive stress and effective saturation is obtained by the pressure plate instrument test is compared with the existing characteristic curve of absorptive stress obtained by tri-axial shear test.It has been found that the relationship between soil suction stress and effective saturation can be well described by direct shear test,each parameter is easy to obtain,and the strength formula based on the curve of suction stress avoids the trouble of measuring matric suction,which can be realized by conventional direct shear test,which is easy to be popularized in engineering practice.3.The Logistic model of soil volume under isotropic compression curve is established by using the Logistic function.Through the analysis and comparison with the existing test data,the compression curve model and the rebound curve model proposed in this paper can reasonably describe the compression characteristics of unsaturated soil.4.The moisturizing deformation characteristics of collapsible loess under different hydraulic effects were studied by unsaturated soil consolidation apparatus,and the onedimensional moisturizing deformation model of collapsible loess was established by Logistic function.However,the results show that the total deformation of collapsible loess under wetting load consists of two parts: compression deformation and moisturizing deformation.Also,the slope of the compression deformation curve is far less than that of the moisturizing deformation part,and the slope of the moisturizing deformation part is opposite to that of the compression deformation part.In addition,the change of volumetric strain is parallel to the corresponding suction curve and related to the humidification path.