Study On Unsaturated Shear Strength Of Loess In Jingyang Based On Conventional Quick Shear

The study about shear strength of unsaturated loess is to provide reasonable values for estimating the bearing capacity,slope stability,retaining wall lateral pressure and surrounding rock pressure.This experimental study is designed to solve the engineering practice problems and obtain a theoretical guideline for estimating the unsaturated shear strength of loess which is more suitable for engineering.We use filter paper to measure soil water characteristic curve of undisturbed loess samples of L1,S1,L5,L9 layers,representing Q3,Q2 and Q1 respectively,which are typical loess coming from Jingyang,Xi’an,Shanxi province.To estimate the parameters of Bishop model,Fredlund model and Vanapalli model,we obtain the shear strength indexes by quick shear test under different moisture content and saturated shear strength indexes by tri-axial consolidated undrained,tri-axial consolidated drained and quick shear test respectively.Based on above study,we obtains the following conclusion:a)the degree of saturation of Jingyang loess at 60 m depth is in 20%-60%,in which soil water characteristic curve from L1 to L9 had significant change.The more dense the soil is,suction is higher at the same water content.b)The saturated effective internal friction angle of undrained quick shear tests is much smaller than that of the drained slow shear test.The effective internal friction angles measured in similar ways are close,and have little correlation with dry density.The effective internal friction of loess by tri-axial undrained consolidated shear test is about 10 degrees,however,it reached 27 degrees tested by consolidated drained method.c)The relationship between the parameter K of unsaturated shear strength in the Vanapalli model and the plastic index is established.We combine the dry density,plasticity index,clay content,Fredlund &Xing equation of the soil water characteristic curve and Vanapalli shear strength model to predict the shear strength of unsaturated loess,which is inspected by Jingyang typical loess layer L5’s quick shear test under the pressure of 100 kPa,the error is less than 40%.