Study On Disintegration Mechanism Of Granite Residual Soil Under Drying-wetting Cycles

Granite residual soil is a kind of unsaturated regional soil widely distributed in the southeast coast of China.Its mineral composition,chemical composition and particle size composition cause its engineering properties to deteriorate and easily disintegrate when encountering water.Moreover,affected by the monsoon climate,Fujian area is in drying-wetting cycles,which provides a good condition for the disintegration and softening of granite residual soil.This phenomenon leads to many landslides and other natural disasters in this area and also causes a lot of problems in geotechnical engineering practice.Therefore,the experiments of water immersion disintegration,atmospheric disintegration and scanning electron microscopy of the granite residual soil under drying-wetting cycles were carried out.The micro parameters of the scanning electron microscopy photos were quantitatively analyzed,and the numerical simulation was carried out to analyze the evolution of the micro structure of the granite residual soil in the process of disintegration.The disintegration mechanism of unsaturated granite residual soil under the effect of drying-wetting cycles is studied from the macroscopic and microscopic aspects.The main work and results of this paper are as follows:1.The experiments of water immersion disintegration and atmospheric disintegration of granite residual soil under drying-wetting cycles were carried out.The disintegration characteristics of granite residual soil under the influence of high-temperature and rainy climate are obtained.The variation rules between disintegration parameters,compaction and times of drying-wetting cycles are obtained.2.The disintegration products of granite residual soil under drying-wetting cycles were observed and tested by electron microscope.The micro shape,distribution and arrangement characteristics of soil particles and pores were obtained.The relationship between micro parameters and the times of drying-wetting cycles and compaction of soil was obtained.The relevance between strength indexes and micro parameters of soil under drying-wetting cycles was calculated.The microstructure model of granite residual soil is established.3.Based on the study of macro engineering characteristics and micro image of granite residual soil,the geometric model is established by software to simulate the process of disintegration and analyze the disintegration mechanism of granite residual soil.The disintegration of soil is a process of stress concentration and failure in the weak part of soil microstructure,constant readjustment of stress field and gradual failure of structure.The microstructure of the soil with high degree of compaction is close,and the contact between particles is mostly point-to-surface and face-to-face contact.The initial force between particles is small,and the disintegration occurs slowly.The drying-wetting cycles lead to the increase of the initial micro cracks in the soil and accelerate the disintegration of the soil.