Multi-scale Structure Study On Shear Failure Of Sliding-zone Soil In Jingyang

The study of shear mechanism and strength characteristics of slip zone soil is the focus of slope safety evaluation.In the existing test methods,there is a disadvantage that the slip zone soil is easily disturbed,especially after the sample water content is increased,and the indoor test sample is difficult to prepare.At the same time,the macroscopic performance of the sliding soil shear properties depends on the internal fine microstructure changes,but the current understanding of the formation mechanism and microscopic mechanism of the slip zone soil is very limited.In response to the above problems,this paper developed a pure shear tester,which can avoid the disturbance of the slip zone soil under high water content in the test.Using macroscopic mechanical test,CT scanning mesoscopic test and scanning electron microscopic test to test the mechanical strength of the slip zone soil,observe the fine microstructure damage inside the slip zone soil,and observe the micro-scale of the shear joint in different shear displacements.Changes in the morphology and structure of millimeter-scale multi-scale minerals.The main research results are as follows:(1)Through the microscopic images obtained by the CT scanning test of the slip zone soil,the structural analysis of the slip zone soil and the distribution characteristics of the pores and calcareous cementation were studied.It was found that the degree of disturbance of the sliding soil along the boundary of the sliding surface was significantly different.The soil in the front part of the sliding soil sample is disturbed by the soil,and the original structure is completely lost.The soil is loose,the surface of the soil is rough,the pores are relatively developed,and the cracks develop.The soil behind the sliding surface is less disturbed,and the soil structure is relatively intact.(2)Electron microscopy was performed on the slip zone soil at 500 times magnification to obtain a microscopic image.The multi-scale microstructure of the shear seam is obtained by image processing technology.It has been observed that there are many agglomerates in the shear band formed by one or several mineral particles being surrounded by tiny particles,and the phenomenon that particles or agglomerates in the shear band support each other is obvious.(3)Based on the existing pure shear test idea,a pure shear tester capable of testing the shear strength of soft soil under high water content was developed.The preliminary laboratory test of the pure shear tester was carried out to complete the shear strength test of the high moisture content sliding soil.(4)Shear seam samples with different shear displacements were prepared using Q2 undisturbed loess.Scanning electron microscopy(SEM)was used to observe the multi-scale microstructure of the shear joint.It was found that under the shearing action,the mineral particles in the middle of the shear joint were removed from the original position and the frictional resistance was increased in the shear joint to make the mineral particles.It is squeezed,smashed,cut and turned into smaller mineral particles.At the same time,the soil particles move in the shear joint,and the friction causes the tiny mineral particles on the shear surface of the shear joint to be detached by the raft,and the shear slit width becomes large,forming a good water guiding channel.It is proved that the secondary occurrence of landslide is related to the loose water guiding channel formed during the initial sliding process of the sliding zone soil.