Experimental Study On The Shear Mechanical Properties Of Interface Of Loess And Hipparion Red Clay

In the loess area of China,all large and medium-sized landslides are loess and red clay interface landslides,among which loess and Hipparion red clay landslides are typical,its mechanical properties of landslide interface change strongly,under the condition of continuous excavation of toe of slope and rainfall,the contact interface will absorb water and soften,which will easily lead to landslides.And this kind landslide is harmful.Therefore,this paper chooses the soil of sliding zone of loess and Hipparion red clay interface as the research object,which is from chenjiapo landslide in Bailuyuan,Xi'an,carries out the experimental research on its interface shear mechanical properties,innovatively develops the sample preparation equipment and visual direct shear apparatus for the interface sample.Through the experiment,the strength and deformation characteristics of the interface samples are obtained,and the influence of interface contact angle,moisture content and dry density on the shear failure mode,shear deformation and strength of the samples was studied,the strength model of interface between loess and Hipparion red clay was established.This provides experimental data parameters for revealing the mechanism of landslide of loess and Hipparion red clay.The detailed research contents and results are as follows:(1)A set of sample making device which can make the rough contact between loess and Hipparion red clay has been developed,and a full-automatic visual direct shear instrument which can carry out the shear mechanics test of interface sample has been developed.The shear stress,horizontal shear displacement and vertical dilatancy displacement of the sample can be tested,and the shear failure process of the interface sample can be photographed and observed during the shear process.The test results show that the equipment runs stably and the test data is reliable.(2)Shear failure mode of interface specimen: the shear failure mode can be divided into three modes: climbing failure,climbing-shear failure and shearing failure.The shear process can be generally divided into four stages: compaction stage,climbing stage,shearing stage and friction stage.The shear failure mode is related to the test conditions.The specimen tends to shear failure with the larger the serration angle,the higher the moisture content and the smaller the dry density.(3)Shear deformation characteristics of interface specimen: the larger the interface contact angle,the lower the moisture content of the specimen and the greater the dry density of the specimen,the more obvious the shear characteristics after the peak value of the shear stress-strain curve.The vertical dilatancy displacement curves of the interface samples show a trend of increasing first and then stabilizing.The dilatancy displacement is related to the failure mode of the samples.The vertical shear expansion displacement of the samples in the climbing mode is the largest,and the shear expansion displacement in the shear mode is the smallest.(4)The change characteristics of interface specimen strength: the larger the interface contact angle,the lower the moisture content of the specimen,and the higher the dry density of the specimen,the higher the strength of the interface specimen.The influence of normal stress on the interface shear strength is more significant than contact angle and dry density of the sample,while influence of moisture content of the sample on the interface shear strength is significant in the normal stress range of 234.165 kpa ? 400 k Pa.(5)Shear strength model of interface specimen: the shear strength of interface specimen of loess and Hipparion red clay changes nonlinearly with normal stress,which is related to the shear failure mode of interface specimen.Therefore,according to the shear failure mode of interface specimen,a strength model formula is established to describe the shear strength change of interface specimen in stages,which can well predict the strength evolution process of the interface specimen.