Shear Properties Of Loess-paleosol And Bedrock Contact Zone

The structural plane is the controlling factor of rock and soil failure and also the sign of the potential development direction of rock and soil failure.The structural plane of loess is formed along with the deposition and evolution of loess.Due to the different genesis,its mechanical properties and traits are also different,and the types of disasters controlled are also different.In this paper,the types of loess structural planes were studied by field investigation,in-situ shear test,indoor triaxial and shear rheology,and the loess-bedrock structure and loess-paleosol contact zone were taken as examples.Focus on its deformation and strength characteristics,and got the following conclusions:（1）According to the cause,the structural plane is divided into primary and secondary.Considering the positional relationship between the structural plane and the loess,it is divided into the interior of the loess and the outside of the loess.Finally,the loess structural surface is divided into loess-paleosol contact zone,loess-bedrock structure surface,loess-soil contact structure zone,deformation zone,joint fissure filling zone and contact slip-slip cover contact zone,totaling 6 major categories and 18 sub-categories.（2）Through in-situ test and laboratory test comparison analysis,it is found that the structural plane strength is less than the loess strength is less than the bedrock strength,that is,the core that determines the stability of the loess-bedrock slope is the structural plane strength.The results of in-situ test of loess-mudstone structure and loess-sandstone surface are better than those of Mohr-Coulomb strength criterion.The Mohr-Coulomb strength expression corresponding to the natural state of the structural plane is obtained:τ_{f mudstone}=0.4233σ+6.4,τ_{f sandstone}=0.1441σ+4.（3）The in-situ shear test of the loess-paleosol contact zone shows that the method of saturation after sample preparation is better.The strain curve of the saturated sample under strain of normal stress is strain hardened,and the shear strain reaches a peak at about 1%.The natural sample has a strain-softening strain curve under high normal stress,and the shear strain reaches a peak at about 3%.The triaxial test of the contact zone shows that the stress-strain curves are softened,in which the elastic phase has a short deformation and the strain is less than1%.The peak strength and the shear strain decrease with the water content and the confining pressure increase.Increased.The Mohr-Coulomb intensity expression of different water content in the loess-paleosol contact zone is proposed:₁..)=₃?1)（）+1)₍（8）（）（4）In the rheological test of the loess-paleosol contact zone,the contact zone soil exhibits typical initial creep and stable creep stages under vertical stress at all levels,but there is no obvious accelerated creep stage.The destruction of the soil occurred more suddenly.The fitting results of the creep constitutive model of the contact zone show that the Mesri model has good adaptability to the contact zone soil,and the logarithmic model and the modified logarithmic model have better fitting results.The fitting results of the Kelvin model and the Burgers model with variable parameters are better,and the self-built fixed parameter model fitting results are also ideal.According to the maximum strain control theory,the long-term strength failure criterion of the power function in the contact zone soil is established,and each parameter is transformed into a function of time t.This result can serve the slope stability prediction of future research areas.