Structural Damage Mechanism Of Granite Residual Soil In Eastern Hunan Under Dry-wetting Cycles Conditions

Synchronization of rain and heat is obvious in Hunan Province.Dry-wet cycling aggravates weathering of granite,damages special structure of granite residual soil,reduces stability of geotechnical engineering,and leads to frequent geological disasters such as small and medium-sized collapses and landslides in Hunan granite region.The research on structural damage mechanism of granite residual soil under dry-wet cycling is of great significance for engineering prevention and control of structural granite residual soil under increasingly extreme weather conditions.The research on structural damage mechanism of granite residual soil under dry-wet cycling is of great significance for engineering prevention and control of structural granite residual soil under increasingly extreme weather conditions.The main research contents and results of this paper are as follows:(1)The physical properties and structural properties of weathered granite residual soil were investigated by grain analysis,XRD and SEM.The test results show that the granite residual soil is mainly composed of mineral components such as quartz,mica,kaolinite and feldspar.Sheet frame structure and cemented block structure domains of soil particles are mainly composed of point contact,line-surface contact,surface-surface contact bridging and cladding.Intergranular pore is small and particles are compact and aggregated.(2)Dry-wet cycling and direct shear tests were carried out.The results show that the structural shear strength of undisturbed soil is the highest and the cohesion of saturated soil is the lowest.The shear strength decreases continuously with the dry-wet cycling process.The shear strength decreases most in the first dry-wet cycling and decreases gradually with the number of times increasing.The structural strength of granite residual soil under dry-wet cycling is characterized by structural parameters,and the regularity of structural damage is summarized.With the increase of vertical stress,the structural property of residual soil decreases without dry-wet cycling.After several dry-wet cycles,the structural properties of residual soil under high stress conditions are relatively high.Structural damage model of granite residual soil under dry-wet cycling was obtained by fitting structural parameters with non-linear surface model.(3)Microstructure changes of granite residual soil after dry-wet cycles were analyzed by SEM image and microstructure parameter extraction.With the increase of the number of dry-wet cycles,the degree of soil aggregation decreases,the large particle group breaks down,the number of small particles increases,and the particle structure becomes more complex.Porosity is growing and the boundary becomes smoother and smoother.Pore system is becoming more and more confused,and the decrease of fractal dimension of distribution indicates that the degree of interconnection and homogeneity of pore is getting better and the change of pore size distribution is getting smaller and smaller.Under hydrodynamic effect,soil structure is destroyed,cracks develop continuously,cementation dissipates and structural damage occurs.Through stepwise regression analysis,it is concluded that the most influential factors of microstructural parameters are particle average area and pore probability Entropy.A regression model of microstructures and structures is established,and the mechanism of structural damage of granite residual soil under the influence of dry-wet cycling is revealed.