Drying-wetting Cycles Induced Changes In Expansive Soil Structure And Its Relationship With Variations In Strength

Expansive soil is a kind of water sensitive material,mineral composition is mainly composed of strong hydrophilic clay minerals(montmorillonite and illite).Expansive soil is sensitive to the natural climate conditions.In the climate of dry and wet alternation,the internal structure of expansive soil can form a large number of micro fractures in the matrix suction.The variation of the meso structure of expansive soil under the action of wet and dry cycles is the root cause of the deterioration of the macro mechanical properties and the key to the failure of the expansive soil slope.Therefore,it is necessary to study the mechanical properties of expansive soil under the action of wet and dry cycles and the changes of its microstructure characteristics.Based on this,the CT scanning of Nanyang expansive soil,which is based on CT technology,is used to quantitatively analyze the characteristics of expansive soil,and then,by means of cluster analysis and stepwise regression analysis,the relationship between the characteristics of expansive soil and low stress shear strength is established by using cluster analysis and stepwise regression method.The main conclusions of this paper are as follows:1.The influence of 1st-4th times of drying-wetting cycles on the structure of expansive soil is bigger,the development of internal fracture was obviously.The influence of 7th-8th times of drying-wetting cycles on the structure is little.Under the same control dry density,the initial control water content can effectively inhibit the cracking of soil.2.The intersections of cracks,number of blocks,the average length and crack rate was basic index to describe the structure and geometric feature,can be used to describe the degree of crack development.Number of crack segments and total length was controlled by the intersections of cracks.Number of blocks reflect block area change rules.The average length reflects Internal crack connectivity.Crack rate can be used to explain the volume change of the soil in general fall.3.After the drying-wetting cycles,the strength attenuation of expansive soil is mainly decrease of cohesion,and the variation of internal friction angle is not significantly.4.With the increase of drying-wetting cycles times,the anisotropy of expansive soils is becoming more and more obvious,and the main performance of the CT is gradually increasing.With the increase of drying-wetting cycles times,the damage variable increases gradually,and the evolution of meso-structure damage is a non-linear accumulating process.CT damage variable and cohesion of expansive soil has a good index decay relationship.