Study On Shear Mechanical Properties Of Sand-loess Under Complex Condition

As a typical geological disaster,the formation and movement of landslides are quite complex process of its mechanism and are affected by a lot of circumstances.Its development,occurrence and motion are the large shear displacement processes that occur along the slip band(surface)and a certain sliding path.This shear process involves the complicated mechanical action of the soil on the sliding path,and influences and controls the instability and motion of the landslide.At present,the mechanism of soil in the landslide disaster mainly focused on the study about the mechanical properties of the sliding zone soil and the determination of strength parameters.Its research content mainly involves strength parameter and determination method of slide zone under the static and dynamic load etc.However,these studies are only for a single research of soil with the same physical conditions,and are rarely involved in shear mechanical properties that the sliding combined with the other geotechnical medium of different physical properties conditions in the process of contact slip.Therefore,it is necessary to carry out the study of mechanical properties of heterogeneous soil composed of two different kinds of soil.In addition,due to the routine test instruments and methods on the limitations of the function,the test results can not reflect the actual landslide under large shear displacement,such as grain orientation arrangement,particle breakage,pore water,etc.Ring shear apparatus is one of the equipment to study mechanical property of the soil under large shear displacement,and its results can more really reveal the actual stress state of the slip.In this paper,by using large high-speed ring shear apparatus,and selecting standard soil,the typical landslides in loess and sand-loess in heterogeneous soil as the object of the experiments,conducts ring shear test under different drainage,normal stress and shear rate,in order to reveal shear mechanical characteristics and its mechanism of different soil in the process of the landslide slip in the large shear displacement,for further research of soil mechanism of landslide disaster shear mechanical properties,and its influence on the landslide movement process to provide theoretical support and analysis basis.The main contents and conclusions of the experiment are as follows:(1)Firstly,mechanical properties and variation mechanism of saturated sands under different normal stresses,shearing rates and pore water pressures were discussed through a continuous large displacement shear test.Research results demonstrated that: In the ring-shear test under drainage conditions,changes of difference between shearing stress and strength of sands are not only related with fine particle movement and structural changes,but also are influenced and controlled by variations of pore water pressure in the shearing process.(2)Secondly,to the moisture content of 12 % loess as the research object,has conducted the undrained condition of ring shear test.The result shows that the shear strength of loess is mainly influenced by shear soil cohesion and internal friction in the process of mutual influence,including its shear stress change curve is strain hardening.(3)At last,does that the upper part is standard sand and the upper part is loess,which are made up heterogeneous soil,was conducted ring shear test.Study results showed that under different drainage conditions,heterogeneous soil consisting of sand and loess had significant differences from loess and sand in aspects of change form of shear stress and shear strength during mutual shearing process.During shearing process,heterogeneous soil consisting of sand and loess presented shearing mechanical characteristics of cohesive soil.The reason for differences of heterogeneous soil consisting of sand and loess from single loess and single sand in aspect of shearing mechanical characteristics under different drainage conditions was mainly related to interaction between sand and loess on shearing surface and pore water state inside soil body near shearing surface.This study is not only promotes the development of soil mechanics,but also provides certain theoretical basis to solve practical engineering geological problems,and there are important academic significance and engineering application value.