Experimental Study Of Saturated Loess Under Permeability And Shear In South Jingyang Plateau

A large number of agricultural water diversion and irrigation activities in the loess plateau of the Loess Plateau,the groundwater level gradually increased,changed the seepage field of the slope of the loess plateau,and made the soil in the inner region of the slope under the superimposed effect of seepage and shear.Affect the mechanical and hydraulic properties of the soil.This thesis takes the saturated loess in the southern plateau of Jingyang as the research object,and studies the permeability and shear strength properties of saturated loess samples under different confining pressures and different osmotic pressures by carrying out triaxial permeability-shear tests of saturated undisturbed and remolded loess,To discuss the permeability-shear mechanism of saturated loess in South Jingyang Plateau,and the conclusions are as follows:(1)During the triaxial penetration-shear test,the permeability coefficient of the saturated loess sample decreases sharply first and then decreases relatively slowly and tends to be basically unchanged;in the low confining pressure state,as the axial strain increases,the saturated loess sample The permeability coefficient curve of the sample has a large decrease,while the decrease is relatively small under high confining pressure;the variation range of the permeability coefficient of the saturated loess sample under different seepage pressure conditions is large and small;at the beginning of the permeability-shear test,saturated undisturbed loess The permeability coefficient of the sample is much larger than that of the saturated remolded loess sample.As the infiltration-shearing continues,the permeability coefficient of the saturated undisturbed loess sample decreases relatively significantly,and the permeability coefficient curve of the saturated loess sample gradually overlaps.(2)As the seepage pressure increases,the deviator stress of the saturated loess sample decreases to different degrees;the stress-strain curve approaches from the initial stage of the triaxial permeability-shear test,and then tends to separate,and the confining pressure states are different.The degree of separation is different;the shear strength of the saturated loess sample increases significantly with the increase of confining pressure,and decreases with the increase of osmotic pressure;with the increase of osmotic pressure,the cohesive force of the saturated loess sample under the total stress decreases significantly,While the effective cohesion is relatively small.Under the same seepage pressure,the cohesion and effective cohesion of the saturated undisturbed loess samples are respectively smaller than the corresponding saturated remolded loess samples;the internal friction angle of the saturated loess samples increases with the infiltration The pressure increases and decreases slightly.(3)In the triaxial permeability-shear test of saturated loess samples,the permeability change mechanism mainly depends on the mutual movement of soil particles under shear action and dynamic adjustment of the arrangement,which in turn causes the pores to change.At the same time,different confining pressures In the state,the kinetic energy of the seepage flow of water under the action of osmotic pressure erodes the soil particles,which in turn causes its structural changes,and ultimately affects the permeability of saturated loess;its shear strength change mechanism depends on the continuous pore water pressure on the soil particles.Erosion can damage the connection between soil particles and gradually disintegrate the structure,so that the cohesion force is significantly reduced.At the same time,the water kinetic energy carries the soil particles to move,reducing the friction between the soil particles when they squeeze and bite each other.The friction angle is slightly reduced.Therefore,the coupled effect of the stress field and the seepage field will degrade the shear strength of saturated loess.