Study On The Development Law Of Cracks In Undisturbed Expansive Soils In A Certain Area Of Chengdu

In this paper,as theoretical development,model test and CT test are used to study the development of fractures of undisturbed expansive soils in Chengdu.The theoretical analysis mainly discusses the mechanism of crack initiation.The model test mainly determines the change of fracture degree in the cracking process of expansive soil,the determination of fracture width and The variation of water content in the development of cracks at different depths of the specimen is also obtained.The distribution of cracks in the soil is also obtained by CT scanning.The main research results are as follows:1.According to the cracking process of soil fissures,the mechanical mechanism of soil cracking is analyzed.The critical conditions of soil cracking are related to the matric suction and tensile strength through elastic theory reasoning,and the force of soil particles is analyzed.Explain the crack cracking process.In addition,through the thermodynamic theory,it is concluded that the temperature influence does not cause the soil to crack,but the depth of influence can be obtained.Finally,the model is simplified by the elastic theory,and the shape of the triangle and the trapezoidal crack are simplified into a rectangle,and the widest width of the fracture theory is obtained,and then the crack width and depth of the sample surface are measured to verify the theoretical analysis.2.Through the model test,the development of the surface crack of the original expansive soil sample during dehydration is obtained.The surface cracking degree of the sample is obtained by photogrammetry and software processing.The results show that the surface cracking degree of the sample during the dehydration process The whole is increasing,but in the rainy season due to air humidity and the like,the swelling of the expansive soil slightly expands,resulting in a slight decrease in the surface cracking of the soil.In this test,the water content of the test soil samples at different depths is obtained by the drilling method.Since the cracks are caused by the change of water content,the depth of the cracks in the sample can be judged according to the change of water content.3.The sample was obtained by dry 7 times wet cycle,and the change of crack surface degree was obtained by photographing and software processing.It was found that the crack degree increased first and then stabilized as the number of dry and wet cycles increased.The sample after 7 dry and wet cycles was scanned by CT to obtain the internal crack development law.The results show that the fracture growth decreases first and then increases with the increase of depth.The simplified three-dimensional modeling of soil fissures is also carried out by CAD processing,which can visually show the distribution law of cracks.It can be seen that the cracks decrease first and then decrease with the increase of depth,which is consistent with the law of crack resolution.In addition,the volume of the fracture is calculated according to the simplified three-dimensional fracture model.4.Discuss the engineering significance of the fracture geometric parameters obtained in the analysis experiment,and propose the relationship between the fracture degree of the body and the surface surface crack of the sample,and convert the fracture rate into a fracture coefficient to the stability of the expansive soil slope with cracks.Subsequent research ideas in the calculation provide reference for further research.