Study On Thermal Induced Cracking Mechanism Of Rock Based On Discrete Element Method

Underground engineering is facing a more complex environment,especially the challenge brought by high stress and high temperature.At present,most of the existing rock mechanics theories are developed under the conditions of shallow layer and normal temperature.Due to the limitation of measurement means,the experiment in high temperature environment is difficult to carry out.Therefore,the study of rock failure law under high stress and high temperature environment has certain limitations.In this paper,according to the environmental characteristics of underground rock engineering,the composition analysis and mechanical experiment of granite are carried out,and the discrete element model is constructed.The thermal crack initiation and propagation of rock under pure thermal stress were studied.According to the material characteristics and occurrence state of rock,the crack initiation mechanism,propagation law and relevant thermal eigenvalues in the process of thermal cracking are studied.The results show that the thermal stress is in dynamic evolution during heating.After the bonding between mineral particles reaches the limit,it breaks and forms thermal cracks.With the increase of heat treatment temperature,the number of thermal cracks increases.200-300℃ is the boundary temperature for the obvious increase of thermal cracks,and the initiation of thermal cracks is concentrated at the edge.When the temperature is high,obvious macro cracks are formed from the center of the rock from the inside to the outside;With the increase of initial axial stress,the thermal sensitivity of rock is enhanced,indicating that the rock is more prone to thermal cracking under high stress state.With the increase of crack angle(α),the thermal sensitivity decreases gradually,which is manifested in the increase of crack initiation temperature,the backward temperature range of severe thermal crack initiation,the number of overall thermal cracks is small,and the overall failure of rock is often caused by the slip at the crack;In the process of thermal cracking,the initial stress field and thermal stress field overlap each other.With the increase of temperature,the axial stress increases gradually.In the rock with existing cracks,the position of thermal crack initiation is the stress concentration at the crack tip.The first control factor of thermal crack propagation is the distribution of isotherm,and the second control factor is the angle of existing cracks;The initiation and propagation of thermal crack under the action of two stress fields are complex,and its unified law is that the initiation and propagation of thermal crack mainly occur in the region where the second invariant changes significantly.The research on thermal cracking of granite can enrich the theory of high-temperature rock mechanics and provide theoretical support for engineering construction and maintenance in complex underground environment and hightemperature rock breaking under high stress.