Research On The Slope Stability And Deterioration Mechanism Of Granite Subjected To The Coupling Effect Of Stress And Freeze-thaw Cycle

The physical and mechanical properties of rocks in cold regions are seriously degraded under the action of high-frequency short-term(day and night)and seasonal freeze-thaw cycles.The above phenomena are susceptible to inducing geological disasters such as frost cracking and freeze-thaw landslides,which seriously affect the stability and safety of geotechnical engineering structures.Furthermore,the actual engineering rock mass undergoes freeze-thaw cycles while also being stressed.Indepth study of the rock damage mechanism under stress-freeze-thaw coupling is closer to the engineering reality.It has important theoretical value and practical significance for the stability control and evaluation of engineering rocks in cold regions.In view of the above,this paper,relying on the national key research and development program project "Key technologies and devices to enhance structural safety and disaster resilience in the key sections"(2021YFB2600604),the Jilin Province Transportation Innovation and Development Support(Science and Technology)Project "Research on monitoring and early warning of typical geologic hazards along the G331 and prevention and control technology"(2021-1-1)and the project of Graduate Student Innovative Research Program of Jilin University "Research on the mechanism of macro-and microscopic deterioration of rocks under the coupling effect of stress,freeze-thaw cycle and chemical erosion"(2023CX053),takes the typical granite of Ji’an area of Jilin Province as the object of research,and adopts indoor experiments,theoretical analyses,and numerical simulation,etc.to study in depth the deterioration mechanism of rock damage under the coupling effect of freeze-thaw cycle and stress.The effect of differential freeze-thaw induced by stress on the stability of rocky slopes was explored.The study aims to clarify the damage mechanism and the evolution of physical and mechanical properties of rocks,and to provide theoretical basis for the evaluation of the stability of geotechnical engineering in cold regions.The main research work is as follows:(1)The freeze-thaw cycling effect leads to the deterioration of granite properties and changes the failure mode of rock damage under load.The nature of energy evolution failure in the loading process of granite after freeze-thaw cycles was explored through freeze-thaw cycle tests and uniaxial compression tests.The transformation of granite failure fracture modes under freeze-thaw cycling was analyzed based on multiple fractal theory.The freeze-thaw granite failure process was discussed with the aid of the Mel-frequency cepstrum coefficient(MFCC)method.A rapid and significant decrease in the MFCC-2 coefficient was used as information on the pre-stabilization precursors of the granite specimens.(2)The mechanism of granite damage development during freeze-thaw cycles was clarified.The evolution characteristics and multiple fractal features of granite pore structure under freeze-thaw cycle were quantitatively analyzed based on Nuclear magnetic resonance(NMR).The changing law of unfrozen water content in granite during freezing and thawing after different numbers of freeze-thaw cycles was investigated.Based on the strain equivalence theory and thermodynamic principles,a theoretical calculation model of freezing strain was constructed and validated,and the contributions of free water and bound water to freezing strain were analyzed.(3)The effect of the presence of stresses on the frost resistance of granite was explored.The effects of stress on the physical and mechanical properties of freezethawed granite were investigated by the coupling test of stress and freeze-thaw cycle.With the support of scanning electron microscope(SEM),the influence mechanism of stress on the frost resistance of granite was analyzed from the macro-micro point of view.Based on the combined acousto-optical technique,the load damage cracking characteristics of the granite subjected to the coupling effect of stress and freeze-thaw cycle were investigated.(4)The influence mechanism of stress on the development of freeze-thaw damage in granite was clarified.The effect of stress on the pore distribution characteristics of freeze-thawed granite was analyzed with the aid of Micro-CT scanning tests,pseudo-color enhancement processing techniques and threedimensional reconstruction.Based on the theory of freeze-thaw damage and the elastic mechanics method,a calculation model of rock pore wall force under stressfreeze expansion stress coupling was constructed from the theoretical point of view.A statistical damage ontology model of the granite subjected to the coupling effect of stress and freeze-thaw cycle was constructed and modified based on damage mechanics theory.The established model can effectively reflect the strengthdeformation characteristics of the granite subjected to the coupling effect of stress and freeze-thaw cycle.(5)With the support of numerical simulation,the differential characteristics of rock frost weathering under the influence of stress and its effect on slope stability were analyzed.The characteristics of fine-scale mechanical parameter evolution of the granite subjected to the coupling effect of stress and freeze-thaw cycle were explored.The numerical model of stress-induced differential freeze-thaw weathering slopes was constructed with calibrated simulation model parameters.The effect of frost weathering differences on slope stability was explored.Rock engineering frost weathering control methods were discussed with respect to the effect of stress on rock frost damage.