Study On The Influence Of Different Factorson The Soil-water Characteristic Curve Ofpurple Soil In Chongqing

Purple soil is widely distributed in southwest China,and it is one of the important special soils in China.The southwest is rich in rainfall and the soil is not thick,under the action of the atmosphere(such as hydraulic scouring,weathering and erosion,wet and dry cycles,etc.)and various chemical and biological effects,the soil is easily disintegrated and changed,and the soil structure becomes loose,it is one of the main causes of disasters such as soil erosion,landslides,soil and water loss.The particle gradation,stress state,and dry density of purple soil will change under the influence of the atmosphere,these factors are important indicators affecting the permeability and soil water characteristics of purple soil.The soil-water characteristics and permeability of the soil are closely related to the erosion resistance of the soil,study the influence of these factors on the permeability and soil water characteristics of purple soil,it has great significance to explore the mechanism and control methods of soil erosion.The thesis mainly researches from the following contents:The firstly,taking the purple soil in Chongqing section of the Three Gorges Reservoir area as the research object,using a multifunctional triaxial instrument,based on Darcy's law,the effects of seepage pressure,confining pressure and geostatic stress on soil permeability were discussed.The result shows:As the confining pressure increases,the permeability coefficient decreases rapidly;The seepage pressure has little effect on the permeability coefficient of purple soil;As the geostatic stress increases,the value of the permeability coefficient gradually decreases,the geostatic stress and confining pressure will mutually inhibit each other's effect on the permeability coefficient.The secondly,the soil-water characteristic curve of the reshaped purple soil was measured using a 1500 pressure membrane instrument,analyze and compare the influence of different granule groups loss on the soil-water characteristic curve of purple soil,the D.G.Fredlund and A.Xing models were used for fitting.The results show:The particle composition of the sample with missing granule groups is composed of remaining large particle size group and remaining small particle size group,the water storage capacity has a negative correlation with the average particle size of the remaining particle size group,a negative correlation with the relative content of the remaining large particle size group,and a positive correlation with the relative content of the remaining small particle size group;Using F-X model for fitting and get the model fitting parameters.As the weighted average particle size of the sample gradually increases,the value of a(reflect the size of the air intake value)gradually decreases,the value of n(reflect the slope of soil-water characteristic curve)gradually increases,and the value of m(related to residual water content)increases first and then gradually flattens.The thirdly,the purple soil in Chongqing was used as the research object,soil-water characteristic tests were performed on samples with different dry densities and different continuous gradations using the pressure membrane device.The result shows:The dry density of the soil sample is greater,the pore structure is more compact,the ability to bind water is stronger,the air intake value and residual volume water content are larger;The particle size is smaller,the adsorption capacity for water is stronger,the residual volume water content and air intake value are greater;Can be fitted using the F-X model,the fitting effect is good,the R~2 is above 0.90.The fourthly,soil-water characteristics tests were performed on purple soil under different geostatic stress using the advanced Stress-Related pressure plate instrument.The result shows:The geostatic stress is greater,the initial mass water content is lower,but with the development of the suction path,the change trend of mass water content is lower with matrix suction increasing,and the gap between the moisture content of the larger geostatic stress sample and the smaller geostatic stress sample gradually narrowed.This shows that it is affected by the greater geostatic stress,the water holding capacity is stronger,manifested as a lower dehumidification rate;The geostatic stress is greater,the bimodal characteristics of the purple soil are more pronounced,the hysteresis effect is lower;With the increase of geostatic stress and matrix suction,the porosity ratio gradually decreases,and the effect of geostatic stress on the porosity ratio is more obvious than the matrix suction,the decrease ratio of the porosity ratio during drying path is greater than the increase ratio of the porosity ratio during wetting path.The influence of different factors on the soil-water characteristics and permeability characteristics of purple soil,it has important reference value for analyzing the foundation treatment,landslide mechanism and soil and water control of purple soil.