Study On Mechanical Properties Of Unsaturated Soil And Structure Interface

With the rapid development of urban rail transit in China,in the process of urban underground construction,it is inevitable to disturb the existing structure and cause the instability of the contact surface between the existing structure and the soil,and most of the urban underground soil Saturated soil,so it is very important to study the mechanical properties of the interface between unsaturated soil and structure.At present,there are few studies on the strength of the contact surface of unsaturated soil at home and abroad,and only some regular properties have been explored,and there is no theoretical analysis of the strength of the contact surface of unsaturated soil.Therefore,this paper proposes a strength model of the contact surface,conducts test verification,and uses the model to analyze actual problems,and finally obtains the following conclusions:?1?In this paper,based on the Bishop effective stress,the strength model of unsaturated soil contact surface is established.The model has a total of five parameters,namely internal friction angle,cohesion,Bishop parameters,and two parameters reflecting the characteristics of the contact surface.The advantage of this model is that it is not necessary to carry out unsaturated soil contact surface test.Using the direct shear test with different water content and the strength test results of saturated soil contact surface,the strength of unsaturated soil contact surface under different water content conditions can be predicted.The validity of the model is verified by the experimental data in the literature.?2?Based on the strength model of unsaturated soil contact surface proposed in this paper,direct shear test of saturated soil,direct shear test of unsaturated soil,direct shear test of saturated soil-structure contact surface,soil-water characteristic curve test,unsaturated soil-structure contact surface Direct shear test.The first four tests are used to calibrate the model parameters,and then predict the strength of unsaturated soil contact surface,and compare the predicted value with the test value to verify the accuracy of the unsaturated soil contact surface strength model.?3?The results of the direct shear test of unsaturated soil are analyzed,and the influence of moisture content and dry density on the strength of unsaturated soil is observed.The results show that the dry density has no effect on the shear strength of saturated loess;for unsaturated loess,as the dry density increases,the shear strength becomes larger,and the corresponding stress-strain curve relationship gradually changes from the hardening type to the softening type;As the water content increases,the shear strength decreases,and the stress-strain curve relationship gradually changes from the softened type to the hardened type.?4?According to the unsaturated soil strength model proposed in this paper,the influence of model parameters and water content on the friction resistance of the pile side is discussed based on ABAQUS.The results show that as the model parameter k₁increases,the friction coefficient of the contact surface increases,resulting in an increase in the frictional resistance of the pile side.The change of the water content leads to the change of the strength parameters of the soil.It is obtained that with the increase of the water content,the frictional resistance of the pile side decreases continuously and has a nonlinear relationship,which further verifies the strength theory of the contact surface proposed in this paper.