Study On Frost Heave Fracture Mechanism Of Single Cracked Rock Mass

Under the action of freeze-heave force of ice,the crack tip of rock mass produces tremendous force and expands damage,and freeze-thaw repeatedly to produce macro-cracks.Based on the engineering research background of freezing method construction in Upal Town Mine,the mechanical parameters of red sandstone material with aquifer of 500m-600 m are selected in this paper,the effect of crack occurrence,width and ice content on frost heave cracking mechanism of ice-saturated cracked rock mass under single temperature drop is studied by RFPA2D-Thermal simulation of real fracture system.The results of this study are as follows:(1)Firstly,collecting and consulting the domestic and foreign literature related to low-temperature failure of rock mass,and recognizing the research status of theory,physical experiment and numerical simulation of mechanical properties of cracked rock similar to crack propagation failure,the deficiencies of current research are summarized according to the above contents,and put forward the main contents of this article.(2)Prefabrication of rock model with unequal width cracks under low temperature to explore the law of generation and propagation of new cracks with unequal width cracks.During the whole process of failure of rock models with different ice content,the accumulative amount of acoustic emission of models with more ice content is obviously higher than that of other models.According to the change of acoustic emission quantity,the failure process of rock models with different ice content can be divided into three stages: In the stage of linear elastic deformation,the damage of model elements is less and the distribution is scattered;in the stage of crack formation and penetration,the scattered elements gradually connect to form cracks and develop forward;in the stage of instability failure,the model is completely destroyed and macro-cracks are formed.Comparing the micro-fracture diagrams of each model,according to the degree of the fracture elements,the models are divided into non-damage zone,damage zone and damage fracture zone.The reasons for the different accumulative acoustic emission are also explained.Stress analysis found that the main reason affecting rock failure is the role of the minimum principal stress(tensile stress).After the failure,the tensile stress of the model drops to zero;the stress of the same location near the crack is different,and the corresponding stress of the crack with more ice will be slightly larger,which means that the element will be damaged first.(3)Prefabrication of rock model with unequal width cracks under low temperature to explore the law of generation and propagation of new cracks with unequal width cracks.The fracture results show that the failure modes of rock models with unequal width cracks are basically the same.The failure modes of rock models with unequal width cracks occur first from the ice in the precast cracks,and then continue to develop and expand along the precast crack tip until they penetrate;Acoustic emission cumulative growth rate and cumulative amount are almost the same,not affected by the width.The crack initiation location,propagation direction and failure mode of the model without precast cracks are quite different from those of the model with cracks,It is obvious that the model with cracks has great influence on the formation of new cracks in rocks.