Study On Mechanical Characteristics Of The Rock And Soil In The Red Soil Layer Of Granite Collapsing Hill

The red soil layer is a layer which has strongest erosion corrosion resistance of granite collapsing hill.It has a protective effect on the entire granite collapsing hill.Learning the nature of their Rock and Soil Mechanics has a great help to the research on the mechanism of granite collapsing hill occur.This study chose three typical red soil layers as the research object in Anxi County,Fujian Province,through field investigation in advance to have a fundamental understanding of the basic nature of these three red soil layers,and then carry out laboratory tests on analyzing the influence of soil organic matter content and soil particle size distribution on the soil liquid limit and plastic limit,and the differences on the shear strength of red soil layer between the undisturbed soil and remodeling soil under different moisture conditions,and the expansion and contraction of the red soil layers.The results showed that:(1)The soil in red soil layer of granite collapsing hill is the high liquid limit clay;Liquid limit and plastic limit did have obvious correlation with soil organic matter content,extreme fine sand content and clay content.Among them,soil organic matter content and clay content was significant positive correlation with liquid limit and plastic limit,and extreme fine sand content was negative correlation with liquid limit and plastic limit.The three factors and soil plastic limit and liquid limit relations fitting equation R2 were 0.803 and 0.834,RMSE values were 0.86 and 2.27.The simulation equation can accurately describe the relationship between liquid limit and plastic limit and the three factors.(2)With the increase of soil moisture,soil shear strength,cohesion and internal friction angle were decreased,but the two indicators of soil shear,cohesion and internal friction angle did not have an obvious correlation with soil organic matter content and fractal dimension relationship;Comparing the indicators of soil shear strength index of the undisturbed soil that measured by direct shear with the restoring soil that measured by triaxial shear apparatus,the former is smaller then the latter when measuring the cohesion while its friction angle is larger.(3)Whether the expansion process or contraction processes of the soil in red soil layer of granite collapsing hill are divided into three stages;With the increase of initial moisture content of the soil,the expansion of the soil in red soil layer is decreased,and contraction of the soil in red soil layer is increase;And with the increasing initial dry density,the expansion of the soil in red soil layer is increased;The expansion and contraction process of the soil is not a reversible process.