Strength Characteristics Of Fully Weathered Phyllite Soils In Guilin Longsheng

As a regional special soil,completely weathered phyllite is formed from metamorphic phyllite after a long time of physical and chemical,weathering and transport,and is widely distributed in Longsheng area of Guilin,Guangxi.Guilin is a typical subtropical climate area,where the environment is hot and rainy.Under the typical climate conditions in this area,the soil mass of the completely weathered phyllite slope is often in the unsaturated state and has experienced a long period of wetting-drying cycle.The soil strength will be significantly affected by the water content and wetting-drying cycle,which will reduce the stability of the slope.Therefore,it is of great significance to study the strength characteristics of completely weathered phyllite soil for the analysis,evaluation and treatment of the slope.This paper takes Guilin Longsheng weathered phyllite soil as the research object,and carries out a series of studies on the core problem of the strength of the weathered phyllite soil,mainly in the following aspects:(1)The water holding capacity of completely weathered phyllite soil was studied by pressure plate and saturated salt solution method.The results show that the higher the dry density of completely weathered phyllite soil is,the higher the intake value is and the better the water holding capacity of soil is.Before 3 cycles,the number of dry-wet cycles of fully weathered phyllite soil increases,and the curve becomes slower with the decrease of air intake value,showing a decrease in water holding capacity.However,after 3 cycles,the water holding capacity of the soil does not change much and reaches a nearly stable state.3.The shear strength of fully weathered phyllite soil was systematically studied to explore the influence of water content,dry density and wetting cycle times on the soil shear strength and establish the shear strength model.The test results show that the dry density is large and the shear strength is high.When the water content is in the range of 5%?40%,the shear strength increases first and then decreases with the water content.At low dry density,the deterioration effect plays a leading role,and the shear strength becomes stable after decreasing with the increase of number of cycles.At high dry density,the density effect plays a leading role,and theshear strength becomes stable after increasing with the increase of number of cycles.(2)The tensile strength of fully weathered phyllite soil was studied by using an improved uniaxial tensile apparatus.The results show that the tensile strength of completely weathered phyllite soil increases with the increase of dry density.In this experimental study on the moisture content range(5% ? 40%),the tensile strength of soil presented double peak curve,the previous peak is mainly due to the quantity of liquid bridge,a peak appeared after the result of the contributions by capillary suction.In addition,the previous model is improved to describe the relationship between the tensile strength and water content of the completely weathered phyllite soil.(3)The shear strength characteristics of completely weathered phyllite soil were studied by means of a quadruple direct shear apparatus.The test results show that the shear strength of soil increases with the increase of dry density.When the water content is 5%?40%,the shear strength increases first and then decreases with the water content.The influence of wetting and drying cycles on fully weathered phyllite soil is mainly shown at low dry density,and the deterioration effect plays a dominant role.The shear strength decreases with the increase of cycles and then becomes stable.At high dry density,the density effect plays a dominant role,and the shear strength increases first and then decreases with the increase of the number of cycles and becomes stable.At the same time,according to the model of content(2),a mathematical expression for the shear strength of fully weathered phyllite soil is proposed.(4)Based on the existing research foundation,the combined strength of fully weathered phyllite is analyzed,and it is considered that the Moor-coulomb criterion is too high to estimate the strength of the tension-shear action zone,and the actual tension-shear failure zone is assumed as a quadratic curve,and the strength formula which can effectively reflect the variation law of the strength of fully weathered phyllite is established.