The thawing and softening effect of frozen sandstone with reference to the evolution of microstructure
In high-altitude and high-altitude areas,the stability of steep mining slopes containing years of frozen layers is controlled by the mechanical properties of frozen rock layers.Excavation of the strata exposes the fro-zen rock layers to the air,and coupled with blasting vibrations or mechanical disturbances during excavation,the frozen rock layers gradually soften and heat melt,leading to a decrease in slope stability.With the continued global climate warming,the thermal thawing softening of frozen rock layers accelerates,further exacerbating the risk of instability in mining slopes.The strength of frozen rocks will soften during the hot melt process,which is the most susceptible stage to failure.Studying the thermal thawing softening law of frozen rocks is crucial for evaluating the stability and safety of frozen strata during the thawing process.This article conducted uniaxial compression tests on frozen rocks at different melting temperatures.Based on the restoration of rock pore struc-ture and precise calibration of microscopic parameters,the particle flow software(PFC2D)was used to simulate the compression failure process of frozen rocks.Based on the analysis of the initiation law and propagation law of microcracks,this paper explores the control effect of pore ice on the thermal thawing softening law of frozen sandstone.The research results indicate that:(1)the strength,elastic modulus and other parameters of frozen rock show a two-stage trend with the increase of temperature.There is a certain temperature between-4℃and-2℃,which causes a sudden decrease in the strength and deformation parameters of the sample.(2)As the temperature increases,the failure of frozen rocks at peak stress gradually shifts from being dominated by mineral particle frameworks to being dominated by ice.When the temperature is less than-2℃,the degree of damage to the frozen rock skeleton is higher;When the temperature is greater than-2℃,the damage to porous ice is more significant.When the temperature is below-15℃,the initiation and propagation of microcracks are main-ly controlled by the contact strength between mineral particles;When the temperature is between-2℃and-15℃,it is mainly controlled by the contact strength between ice particles and ice minerals;When the tempera-ture is greater than-2℃,it is mainly controlled by the contact strength between ice particles.(3)By analyzing the supporting and bonding effects of pore ice during the load failure process of frozen rocks,it was found that between-6℃and-4℃,the bonding strength between ice particles and between ice minerals rapidly decayed,leading to a weakening of the supporting and bonding effects of ice,which is the essential reason for the rapid weakening of mechanical properties in this temperature range.For high-altitude and high-altitude areas,the ther-mal thawing softening of frozen rock layers is a core process related to their stability and safety.Therefore,studying the thermal thawing softening law and load failure process of frozen rocks is of great engineering signifi-cance.
frozen rockthawing and softeningmicroscopic structuremicrocrack propagationPFC2D
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