| The large-scale development of the western region and the"Silk Road Economic Belt"are important development strategies in China,which makes more and more geotechnical projects appear in cold areas,which have the characteristics of large temperature difference between day and night,long duration of low temperatures,and obvious alternation of four seasons,so these geotechnical projects are inevitably affected by the freeze-thaw cycle.Rock is the product of natural geological action,there are micro-fractures,intergranular voids,lattice boundaries and other defects,under the action of freeze-thaw cycle,these defects will continue to develop,eventually leading to the decline of rock mechanical properties,thereby threatening the stability of geotechnical engineering.Therefore,this thesis uses indoor experiments and numerical simulation methods to explore the influence of different freeze-thaw cycles on the physical and mechanical properties of red sandstone,and uses SEM to analyze the freeze-thaw damage mechanism from a microscopic perspective.The main research contents are as follows:（1）The apparent characteristics and volume changes of red sandstone with different numbers of freeze-thaw cycles were studied,and the effects of freeze-thaw cycles on the physical properties of red sandstone were analyzed and combined with electron microscopy scanning techniques to reveal the mechanism of freeze-thaw cycle damage from a microscopic perspective.（2）By conducting conventional triaxial mechanical tests on red sandstone with different numbers of freeze-thaw cycles,the effects of freeze-thaw cycles on the strength,deformation and damage characteristics of red sandstone were analyzed,and based on the results of mechanical tests,the damage evolution equation of rocks under the joint action of freeze-thaw and load was established with the elastic modulus as the damage factor,and the damage evolution law of red sandstone under the joint action of freeze-thaw and load was analyzed.（3）By introducing water particles into the particle flow software PFC2D,a numerical model of water-saturated red sandstone was established to simulate the effects of freeze-thaw cycling on the rock by assigning expansion coefficients to water particles,and the development of microcracks inside the specimen during multiple freeze-thaw cycles was obtained,and the deformation characteristics and strength characteristics of the specimen after experiencing freeze-thaw cycling were simulated,and the evolution law of cracks with axial strain during the loading of the specimen was analyzed.There are 59 figures,6 tables and 90 references in this thesis. |
