Study On Mechanical Properties And Failure Characteristics Of Loess-Red Clay Contact Interface

Because the upper loess of the landslide at the loess-red clay contact surface is highly permeable,and the lower red clay is an impermeable layer,rainwater tends to collect on the contact surface of the loess and red clay,forming a slippery zone.In actual investigation,it is found that the sliding surfaces of this type of landslide are not all located on the loess-red clay contact surface.In this paper,taking Naopanliang landslide and its rock and soil mass in Fugu County as the research object,the mechanical properties and failure characteristics of loess-red clay contact samples under different moisture contents,confining pressures and contact angles are studied through geotechnical tests and numerical simulations,combined with the deformation and failure modes of the loess-red clay contact interface at different dip angles and burial depths in actual landslides,the formation mechanism of the landslide sliding surface at the loess-red clay interface was explored,and the following main research results were obtained:(1)The internal friction angle of loess and red clay decreased with the increase of water content,the cohesion of red clay first increased and then decreased with the increase of water content,the cohesion of loess continued to decrease with the increase of water content,and the resistance to loess was higher.Compared with loess,red clay has higher cohesion and lower internal friction angle.(2)Through indoor triaxial shear test and numerical simulation triaxial shear test of the contact sample,it is concluded that with the increase of water content,the decrease of confining pressure and the increase of contact angle,the failure mode of the sample gradually changes from The bulging failure of red clay transformed into the bulging failure of the whole sample and the bulging failure of loess.(3)The shear strength of the contact sample is greatly affected by the failure mode of the sample.When the failure mode is bulging failure of loess or bulging failure of red clay,the shear strength is the shear strength of complete loess or complete red clay.When the sample fails as a whole,the shear strength is between loess and red clay;the shear strength of the contact sample is analyzed from the mechanical point of view.When the failure mode is the same,with the increase of the contact angle,the shear strength of the sample first increases and then decreases,and reaches the peak when the contact angle is π/8+φ/4.(4)The instability and failure process of the Naopanliang landslide was simulated,and the deformation and failure characteristics of the loess-red clay interface under different dip angles and burial depths were analyzed.Combined with the formation mechanism of the shear band of the contact sample obtained from the laboratory test and numerical simulation,it is considered that with the contact With the increase of the inclination angle and the decrease of the buried depth of the contact surface,the formation position of the landslide sliding surface at the loess-red clay contact surface is easy to change from the lower red clay to the upper loess.