高渗透压脆性岩石循环蠕变宏细观力学机理研究

Mechanism of Micro and Macro Mechanics in Brittle Rocks During Cyclic Creep Under High Seepage Pressure

高渗透压、围压及轴向循环静态加卸载共同作用下,脆性岩石循环蠕变力学特性对深部地下工程围岩稳定性评价有着重要意义。目前,针对岩石内部细观裂纹反向滑动及已扩展裂纹闭合恢复机理的研究极为欠缺。本文基于轴向加载、围压与渗透压共同作用下岩石内部初始裂纹面正向滑动诱发的翼型裂纹扩展模型,引入轴向卸载、围压与渗透压共同作用下的初始裂纹面反向与静止滑动力学特性,解释了已扩展翼型裂纹的恢复机理,建立了一种考虑轴向加卸载、围压与渗透压共同作用下,初始裂纹面正向、反向或静止滑动的应力强度因子表达式。在此基础上,结合亚临界裂纹演化法则、裂纹与应变关系及Hooke–Kelvin模型,提出一种岩石内部高渗透压、外部围压与轴向循环加卸载共同驱动翼型裂纹扩展、恢复作用下的循环蠕变宏细观力学模型,该模型描述了岩石完整的弹性、黏弹性、塑性变形行为。研究了高渗透压对初始裂纹面正向滑动与翼型裂纹扩展诱发的脆性岩石弹–黏–塑性应力–应变曲线影响,为弹–黏–塑性循环蠕变的应力、弹性模量参数选取提供依据。分析了高渗透压对初始裂纹面正向、反向、静止滑动与翼型裂纹扩展、恢复诱发的循环蠕变中黏弹性应变ε1ve、纯塑性应变ε1p及总应变ε1的影响。讨论了渗透压对弹性回弹应变、与已扩展裂纹恢复相关的塑性回弹应变、循环蠕变失效时间和失效应力的影响,并研究了围压对弹–黏–塑性循环蠕变应变的影响。研究结果为高渗透压地下工程围岩循环蠕变寿命评价与预测提供了一定的参考。

Cyclic creep mechanical properties of brittle rock under the combined influence of high seepage pressure,confining pressure,and cyclic axial loading and unloading are of great significance to the stability evaluation of surrounding rock in deep underground engineering.The mechanism of the reverse sliding of the crack and the recovery of the extended crack is rarely studied.An expression of stress intensity factor for forward,reverse,or static sliding of the initial crack surface under the combined action of axial loading and unloading,confining,and seepage pressures was established,which was based on the wing crack extension model by forward sliding of the initial crack surface in the rock under the combined action of axial loading,confining pressure,and seepage pressure.The expression introduces the reverse and static sliding mechanical properties of the initial crack surface under the combined action of axial unloading,confining pressure,and seepage pressure to explain the recovery mechanism of the extended wing crack.A micro-macro mechanical model of cyclic creep was established under the action of wing crackgrowth and recovery driven by high internal seepage pressure,external confining pressure,and axial cyclic loading and unloading,which combined with the subcritical crack law,crack-strain model,and Hooke–Kelvin model.The complete elastic,viscoelastic,and plastic deformation of rock was described.The influence of high seepage pressure on elastic–visco–plastic stress–strain curves induced by forward sliding of initial crack surface and wing crack growth of brittle rocks was studied,which provided a basis for the selection of model parameters of applied stress and elastic modulus in cyclic creep.The effects of seepage pressure on forward,reverse,and static sliding of the initial crack surface,and visco-elastic strainε1ve,plastic strainε1p,and total strainε1 induced by wing crack growth and recovery in cyclic creep were analyzed.The effects of seepage pressure on the elastic rebound,plastic rebound caused by crack recovery,failure time,and stress of cyclic creep were discussed.The effects of confining pressure on the elastic–visco–plastic cyclic creep strain were also studied.The study results are meaningful for the evaluation and prediction of fatigue life of underground engineering rock bodies under high seepage pressure.