为研究三轴循环加卸载条件下三山岛花岗岩细观能量演化规律,采用颗粒流理论确定了花岗岩的应力门槛值(起裂应力σci、损伤应力σcd和峰值强度σf),研究了应力门槛值对应的边界能、应变能(线性接触应变能和平行黏结应变能)、耗散能(摩擦能和阻尼能)、动能随围压变化的规律,并从能量角度建立了岩爆倾向性评价指标Wx. 结果表明:三山岛花岗岩不同围压下相应的σci/σf位于37.0%~44.8%区间,σcd/σf位于81.2%~89.0%区间,随着围压的增大,起裂边界能、应变能和耗散能呈线性关系增加,损伤(峰值)边界能、应变能和耗散能呈指数关系增加;其中耗散能受围压影响最为敏感,增幅倍数最大,其次是边界能,最后为应变能. 围压对起裂应变能比例影响不大,损伤和峰值应变能比例随围压增大缓慢减小,峰值应变能比例下降幅度最大. 基于岩爆倾向性评价指标Wx可知,当围压在20 MPa内,三山岛花岗岩岩爆倾向性相对较小;当围压达到30 MPa时岩爆倾向性开始迅速增加. 研究成果为岩爆倾向性的评价提供了新的参考指标,进一步为井下岩体工程的稳定性研究提供了新思路.
To study the meso-energy evolution of Sanshandao granite under triaxial cyclic loading and unloading, the stress thresholds (the crack initiation stress σci, crack damage stress σcd, and peak stress σf) of Sanshandao granite were determined; the variation law of the boundary energy, strain energy (linear contact strain energy and parallel bond strain energy), dissipation energy (friction energy and damping energy), and kinetic energy corresponding to each stress threshold with confining pressures was analyzed; and a new index Wx for evaluating the rock burst proneness was established from the perspective of energy based on a simulation using PFC3D. The results show that the corresponding σci/σf is in the range of 37.0% to 44.8%, and σcd/σf is in the range of 81.2% to 89.0% under different confining pressures. With the increase of confining pressure, the boundary energy, strain energy, and dissipation energy of the crack initiation increase linearly, and the boundary energy, strain energy, and dissipation energy of the crack damage and peak increase exponentially. Among them, the dissipation energy exhibits the maximum increment with the change in confining pressure, followed by the boundary energy, and then the strain energy. The confining pressure has little effect on the proportion of the strain energy of crack initiation. Moreover, with increasing pressure, the proportion of the crack damage and the peak strain energy decrease slowly; however, the proportion of peak strain energy decreases to a greater extent. According to the new index Wx for the evaluation of the rock burst proneness, when the confining pressure was less than 20 MPa, the rock burst proneness of Sanshandao granite was relatively small, and when the confining pressure reached 30 MPa, the rock burst proneness began to increase rapidly. This study provides a new reference index for the evaluation of rock burst proneness and further provides a new idea for the stability study of underground rock mass engineering.