Study On Crack Development Law Of Expansive Soil Under Natural Conditions

Expansive soil is a highly hydrophilic clay composed of clay minerals such as montmorillonite and illite.After being immersed in water,the volume will swell sharply,and after drying and losing water,the volume will shrink to produce cracks.This feature has led to a series of engineering geological problems,such as: building collapse,foundation damage,slope instability,etc.Therefore,it is particularly important to study the characteristics of cracks.This paper takes the expansive soil in Sheqi County,Nanyang City as the research object to study the changes in its permeability and fracture characteristics under natural conditions.The main research contents of this paper are as follows:(1)Research on the development process of expansive soil cracksThrough observation experiments on model soil column cracks under natural outdoor conditions,it is found that the development law of expansive soil cracks can be divided into 5 stages.Stage 1: The main cracks are developed,when cracks appear on the surface of the soil,the number and width of the cracks increase accordingly;Second: the development stage of level Ⅰ minor fissures,the soil near the main cracks cracks,the number of cracks is often narrow;stage 3: the development stage of levelⅡ minor cracks,the soil near the level Ⅰ minor cracks appear smaller cracks,The width of the first major fissures is reduced;Stage 4: Slow development stage 1,secondary fissures continue to develop,the widths of major fissures and secondary fissures continue to shrink,and the development speed of fissures is significantly slowed down;final stage: fissures The development stops,the distribution of the cracks no longer changes,the vertical and horizontal cracks cut the soil into many pieces of "hexagonal" shapes,and the "edges and peeling phenomenon" appears on the boundaries of the cracks.(2)Research on the development law of cracks in expansive soilBased on the classification theory,it is found that the fracture rate and analysis dimension of expansive soil can better characterize the development law of fractures,and the relationship between the fracture rate and the fractal dimension over time is similar and has a good linear correlation.With the passage of time,the crack rate and fractal dimension show an overall pattern of increasing first,then decreasing,and finally stable,and the degree of compaction has a significant effect on the development speed of the cracks,and the soil with low degree of compaction develops faster.(3)Research on the permeability of expansive soilUsing the soil moisture sensor and observing the drainage at the bottom of the model bucket,the permeability characteristics of the expansive soil were studied,and it was found that the permeability of the soil column model was extremely poor in the early stage of crack development in the expansive soil;in the middle stage of the crack development,the permeability of the soil column model was improved In the middle and late stages of the development of the cracks,the soil column shrinks as a whole,which separates from the wall of the model barrel,and atmospheric precipitation flows directly into the bottom drain pipe along the wall of the barrel.