Shear Strength Characteristics Of Unsaturated Loess In A Wide Range Of Suction

Loess is a kind of unsaturated soil,which has the characteristics of wide distribution,loose structure and poor engineering properties.In engineering construction,the shear strength of unsaturated soil is a key problem in the stability analysis of unsaturated soil engineering,and the shear strength research is a necessary means to analyze the stability of engineering soil.The shear strength is closely related to the matrix suction.It is an important method to study the relationship between the matrix suction and the unsaturated shear strength of unsaturated soil by laboratory test.In this paper,from the point of view of the influence of matrix suction on the shear strength of soil,taking four groups of loess in Luoyang as the research object,the full-automatic triaxial apparatus is used to carry out triaxial shear tests on the soil samples which are in a wide range of suction,so as to obtain the change rule of the strength characteristics of unsaturated loess with the matrix suction in a wide range of suction.The pressure plate apparatus system made by Geo-Experts is used to carry out soil tests on the soil samples in order to obtain the soil-water characteristic curve.And the slope stability under the condition of natural precipitation is calculated and analyzed by using numerical simulation software.The research results of this paper are as follows:(1)Four groups of remolded loess samples with different suction(suction values of3.29 mpa,38Mpa,113.8mpa and 367.54mpa)were prepared by steam balance method.Then,the unconsolidated undrained triaxial shear test was carried out on the samples after suction balance by using full-automatic triaxial apparatus.The results show that the stress-strain curves of unsaturated remolded loess with different suction can be divided into two types:strain hardening type and strain softening type.In this suction range,the shear strength and cohesion of unsaturated loess have a non-linear positive correlation with matrix suction,and the increase rate decreases with the increase of matrix suction.With the increase of matrix suction,the internal friction angle is basically unchanged.(2)The soil-water characteristic curve of four groups of loess is measured by the 5bar pressure plate apparatus system made by Geo-Experts.With the increase of matrix suction,the moisture content of the sample decreases gradually,and the change rate shows obvious stage characteristics.It is found that the physical properties of soil have an effect on the shape of soil water characteristic curve.The higher the dry density is,the smoother the soil water characteristic curve is.The smaller the dry density is,the steeper the soil water characteristic curve is.The saturated water content of the sample has a negative correlation with the dry density,and the residual saturation has a positive correlation with the dry density.(3)Based on the field geological survey and a typical slope example,the slope stability under rainfall conditions is analyzed and calculated by using the Geo-studio numericalsimulation software system.It is confirmed that the matric suction has a decisive influence on the stability of loess slope.