Study On The Tensile Properties Of Collapsed Soil And Its Influence On The Stability Of Collapsed Soil

In view of the instability of the collapse slope in the development of granite,taking a collapse in Tong cheng County,Xian ning City,Hubei Province as the research object,the basic characteristics of different layers of collapsing soil are studied through the combination of field investigation and laboratory test,and the internal material basis of the cause of the collapse erosion is revealed.This paper studies the tensile properties of different layers of soil under different influence factors,analyzes the influence of dry wet cycle effect on the attenuation of tensile strength,and discusses the water holding mechanism and fracture surface characteristics of different layers of soil under different water content,based on the tensile strength model of a single soil mass,a prediction model of the tensile strength of the collapsing soil is established to analyze the influence of the tensile properties of the soil mass on the stability of the collapsing soil.the results are as follows:(1)The moisture content has an obvious effect on the tensile strength of collapsing soil.The characteristic curve of tensile strength is single peak type,and the peak value of tensile strength appears near the moisture content W_C(24.4%)of topsoil,laterite and transition layer,while the peak value of tensile strength appears at the moisture content W_C(25.8%)of sand layer.There is a positive correlation between the axial tensile elongation and the radial shrinkage length of different layers of collapsing soil with the water content,and the linear function relationship with high correlation coefficient is fitted between the axial tensile rate and the radial shrinkage rate and the water content(except that the radial shrinkage and the water content of the sand soil are exponential functions).(2)The dry density has an obvious effect on the tensile strength of different layers of collapsing soil.With the increase of dry density,the tensile strength of the soil in each layer of the avalanche increased gradually.The dry density of the soil in each layer increased from 1.30 to 1.45,and the corresponding tensile strength increased by 1.79,2.04,1.96 and 1.99 times respectively.And the tensile strength of different layers of soil is also different under the same dry density.The overall tensile strength of different layers of soil is:laterite layer>transition layer>topsoil layer>sand layer.(3)The tensile strength of different layers of soil is increasing linearly with the increase of the ratio of height to diameter.The tensile strength of different layers of soil is different under the same ratio of height to diameter.Under the influence of the ratio of height to diameter,the tensile strength of different layers of soil is as follows:transition layer>topsoil layer>laterite layer>sandy layer.In the process of height diameter ratio increasing from 1.0 to 2.1,the surface soil layer,laterite layer,transition layer and sandy soil layer increased by 1.69,2.31,1.88 and 2.26 times respectively.(4)With the increase of the number of dry and wet cycles,the tensile strength of the collapsing soil gradually decreases,and finally tends to be stable.The attenuation of the tensile strength of different layers of soil is mainly concentrated in the first three dry and wet cycles.The attenuation ratio of the tensile strength of topsoil,laterite,transition layer and sandy soil layer reaches 90%,82%,83%and 90%respectively,and the overall table of the tensile strength of different layers of soil is as follows:Now it is transition layer>laterite layer>topsoil layer>sand layer.Based on the experimental results of soil tensile strength under the influence of dry and wet cycles,this paper analyzes the effects of different depths of soil and the number of dry and wet cycles,and constructs the prediction model of tensile strength attenuation by means of data simulation.Through analysis,it is found that the prediction value of tensile strength model has a high correlation with the measured value(R~2=0.97).(5)Based on the soil water characteristic curve of different layers of collapsing soil and considering the influence of soil particles,the water holding mechanisms of three kinds of water content ranges of low(18%-22%),medium(22%-30%)and high(30%-saturated)are proposed,which are soil capillary water holding mechanism,aggregate water bridge connection water holding mechanism and aggregate water holding mechanism.Based on the theory and model of single soil tensile strength,a modified model is proposed to describe the tensile strength of different layers of soil,and the results can provide theoretical guidance for the study of the stability of collapsing soil.