应力-渗流耦合作用下不同卸荷路径对砂岩损伤特性及能量演化规律的影响研究

Influence of unloading paths on sandstone damage characteristics and energy evolution law under stress-seepage coupling

岩体灾害发生的本质是能量驱动下的一种失稳现象,受开挖卸荷扰动影响导致的岩体结构破裂失稳是诱发采场突水等动力灾害的主要原因之一。为探究开挖卸荷过程对岩体结构破裂的影响,明晰围岩劣化损伤规律及突水等动力灾害孕育机制,针对应力-渗流耦合因素影响下岩石损伤特性及能量演化规律研究较少的特点,采用Rock Top多场耦合试验仪,在应力-渗流耦合作用下对砂岩开展了常规三轴(C组)、不同初始损伤程度常规卸围压(W组)及循环加卸围压(X组)3种应力路径下的岩石损伤特性及能量演化规律试验研究。试验结果表明:岩石能量演化规律与应力-应变曲线具有明显相关性,基于岩石弹性应变能演化特征,将常规三轴压缩(C组)下岩石应力-应变曲线分为5个阶段,并对每个阶段U_(1)、U_(3)、U_(e)、U_(d)及渗透率变化特点进行了详细阐释(U_(e)为弹性应变能,U_(d)为耗散能,U_(1)为轴向应力对岩石做正功转化的岩石应变能,U_(3)为做负功所释放的应变能);常规卸围压过程中,U_(1)、U_(3)演化规律与C组岩石基本一致,但U_(3)负增长更为显著,岩石输入能逐渐从以U_(e)为主导转变为以U_(d)为主导,初始损伤程度对该规律无明显影响,卸围压过程中渗透率呈波动上升趋势,围压与渗透率呈负相关;循环加卸围压过程中,各能量演化规律与W组岩石基本一致,仅因时间效应而导致能量积累量存有差异。整体来看,无论何种应力路径,峰前阶段岩石均以U_(e)为主导,以能量存储为主,峰后阶段则以能量释放及耗散为主,轴向应力加载是U_(e)得以快速积累的主要影响因素,围压改变不足以引起U_(e)发生较大变化,轴向载荷作用为工程致灾的主要影响因素。此外,岩石损伤变量与围压存在明显负相关,围压越大,岩石U_(e)释放比例越小,岩石损伤越小,围压束缚作用可有效提高岩石储能能力并抑制岩石能量的耗散与释放。

Rock mass disasters are caused by instability driven by energy within the rock mass.The excavation and unloading disturbance can lead to fractures and instability in the rock mass structure,which is a major cause of dynamic disasters such as water inrush in stopes.To understand the influence of excavation unloading on rock mass structure fractures and to clarify the degradation law of surrounding rock and the mechanism of dynamic disasters like water inrush,this study focuses on the characteristics of rock damage and the evolution of energy under stress-seepage coupling factors.Using the Rock Top multi-field coupling tester,the study investigates the rock damage characteristics and energy evolution under three stress paths:conventional triaxial compression (group C),conventional unloading confining pressure with different initial damage degrees (group W),and cyclic loading and unloading confining pressure (group X) under the influence of stress-seepage coupling.Based on the evolution characteristics of rock elastic strain energy,the stress-strain curve of rock under conventional triaxial compression (group C) is divided into five stages,and the characteristics of U_1,U_3,U_e,U_(d) and permeability change in each stage are explained in detail (U_(e) is the elastic strain energy,U_(d) is the dissipated energy,U_(1) is the strain energy of the rock transformed by the positive work done by the axial stress on the rock,and U_(3) is the strain energy released by the negative work).During the conventional confining pressure unloading process,the evolution law of U_(1) and U_(3) is similar to that of group C rock,but the negative growth of U_(3) is more significant.The rock input energy gradually shifts from U_(e) to U_d,and the initial damage degree has no significant influence on the law.During the confining pressure unloading process,the permeability shows a fluctuating upward trend,and the confining pressure is negatively correlated with the permeability.In the process of cyclic loading and unloading confining pressure,the energy evolution law is similar to that of group W rock,with energy accumulation differing only due to time effects.On the whole,regardless of the stress path,the pre-peak rock is dominated by U_e,representing energy storage,while post-peak rock is dominated by energy release and dissipation.Axial stress loading is the main influencing factor for rapid accumulation of U_e,while the change in confining pressure is not enough to cause a large change in U_e.Axial load is the primary factor influencing engineering disasters.Furthermore,there is a significant negative correlation between rock damage variable and confining pressure.The larger the confining pressure is,the smaller the U_(e) release ratio of rock is,and the smaller the rock damage is.Confining pressure restraint effectively enhances the energy storage capacity of rock and inhibits the dissipation and release of rock energy.