A study of the relationship between shear strength and microstructure of laterite under drying and wetting cycles

In view of the objective reality of drying and wetting cycles which caused by the rise and fall of the reservoir water of the laterite reservoir in Yunnan, this article examines the change law of shear strength and microstructure of laterite under the action of drying and wetting cycles, and reveals the internal relationship between the shear strength and microstructure of laterite under the action of drying and wetting cycles. The results can provide the basis for studying the instability of the laterite reservoir. Simulation of the effect of drying and wetting cycles of red reservoir caused by reservoir water immersion and reservoir water level rise and fall is conducted by carrying out drying and wetting cycle tests of the clay sample and using geotechnical experiments and related theoretical analyses. The results show that: (1) Under certain initial dry density conditions, the cohesion, internal friction angle and shear strength of the laterite decrease with the increasing number of drying and wetting cycles, and it will keep stable when the number of times of drying and wetting cycles is 10. (2) The microstructure of the laterite is changed by drying and wetting cycles. When the initial dry density is 1.2, 1.3 and 1.4 g/cm³, respectively, the number of times of drying and wetting cycles rises to 10, the number of the laterite particles decreases by 45.4%, 38.2% and 35.7%, respectively, the porosity increases by 52.6%, 45.9% and 40.4%, and the pore area increases by 64.4%, 58.2% and 50.8%, respectively. (3) Under the drying and wetting cycles, there is a positive correlation between the cohesion of the laterite and the degree of orientation and average circularity of the laterite, and the correlation coefficients R are 0.985 and 0.923. There is a negative correlation between the internal friction angle and the porosity and pore area, and the correlation coefficients R are -0.936 and -0.912. The change of microstructure of the laterite is caused by drying and wetting cycles, which causes the changes in the macroscopic mechanical properties of the laterite.