The Study On Moistening Test And Constitutive Model Of Structural Loess

Loess has special structure and water sensitivity,which is the matter why loess in the dry state has great strength,once mixing the water it is very easy to destroy.In practical engineering,the soil mass is not really destroied in the saturation state,and with the change of water content,soil strength is a dynamic process.However,the experimental method is not able to simulate this process very well at present.In this paper,the triaxial test was carried out by adding ice particles in the sample,the humidifying time is controlled by the melting of the ice particles.And then,a reasonable method to ensure the low temperature environment has been found.Based on the experiment,the expression of the joint strength failure line of tensile and compressive shear stress path test is determined.The coordinate transformation is applied to the Tsinghua elastoplastic model,which model that reasonably considering the tensile strength can be obtained.Finally,the model is validated and the conclusions are as follows:(1)In order to solve the problem that the low temperature environment is difficult to be controlled,the key operation is determined:precooling of sample preparation;arounding the triaxial shear confining pressure ventricular,an ice bag is wrapped and frozen before the test;during the test,the confining pressure ventricular was added the ice water and wrapped cold compress ice bag around;The technical difficult problem of low temperature environment has better solved.(2)This paper completed two kinds of triaxial test(conventional and ice humidification)of remolded loess under four different moisture content.Comparing the two kinds of test results,it is found that the trend curve of the two experiments is consistent.When the moisture content is low,the peak value of the triaxial stress and strain curve of humidification by ice is slightly lower than that of the conventional humidification,and with the increase of moisture content,the two approaches are gradually approaching.(3)Tensile shear strength and compressive shear strength are two important components of structural loess mechanical properties.Using the joint strength failure line based on tensile and compressive shear stress path test to replace the critical state failure line in Tsinghua model.It can reflect the influence of tensile strength on the deformation of loess more reasonably.(4)Using coordinate transformation,without changing the original Tsinghua model yield surface form,transform the joint strength theory into another stress space inside the M-C criterion.The strength failure line of curve form is difficult to calculate and error prone in the derivation of constitutive model can be solved.(5)The model is validated by three axis test with different test conditions,and the results show that the model is reliable.