ZHANG Pei-sen, XU Da-qiang, YAN Wei, et al. Influence of unloading paths on sandstone damage characteristics and energy evolution law under stress-seepage coupling[J]. 2024, 45(2): 325-339.
DOI:
ZHANG Pei-sen, XU Da-qiang, YAN Wei, et al. Influence of unloading paths on sandstone damage characteristics and energy evolution law under stress-seepage coupling[J]. 2024, 45(2): 325-339.DOI: 10.16285/j.rsm.2023.0204.
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U1、U3、Ue、Ud及渗透率变化特点进行了详细阐释(Ue为弹性应变能,Ud为耗散能,U1为轴向应力对岩石做正功转化的岩石应变能,U3为做负功所释放的应变能);常规卸围压过程中,U1、U3演化规律与C组岩石基本一致,但U3负增长更为显著,岩石输入能逐渐从以Ue为主导转变为以Ud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Ue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Ue得以快速积累的主要影响因素,围压改变不足以引起Ue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Ue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 massdisasters are caused by instability driven by energy within the rock mass. Theexcavation and unloading disturbance can lead to fractures and instability inthe rock mass structure
which is a major cause of dynamic disasters such aswater inrush in stopes. To understand the influence of excavation unloading onrock mass structure fractures and to clarify the degradation law of surroundingrock and the mechanism of dynamic disasters like water inrush
this studyfocuses on the characteristics of rock damage and the evolution of energy understress-seepage coupling factors. Using the Rock Top multi-field couplingtester
the study investigates the rock damage characteristics and energyevolution under three stress paths: conventional triaxial compression (groupC)
conventional unloading confining pressure with different initial damagedegrees (group W)
and cyclic loading and unloading confining pressure (groupX) under the influence of stress-seepage coupling. Based on the evolutioncharacteristics of rock elastic strain energy
the stress-strain curve of rockunder conventional triaxial compression (group C) is divided into five stages
and the characteristics of U1
U3
Ue
Ud and permeability change ineach stage are explained in detail (Ue is the elastic strainenergy
Ud is the dissipated energy
U1 is the strain energy of the rock transformed by the positive work doneby the axial stress on the rock
and U3 is the strain energyreleased by the negative work). During the conventional confiningpressure unloading process
the evolution law of U1 and U3 is similar to that of group C rock
but the negative growth of U3 is more significant. The rockinput energy gradually shifts from Ue to Ud
and the initial damage degree has no significant influence on the law. Duringthe confining pressure unloading process
the permeability shows a fluctuatingupward trend
and the confining pressure is negatively correlated with thepermeability. In the process of cyclic loading and unloading confining pressure
the energy evolution law is similar to thatof group W rock
with energy accumulation differing only due to time effects. Onthe whole
regardless of the stress path
the pre-peak rock is dominated by Ue
representing energy storage
while post-peak rock is dominated by energy release and dissipation. Axialstress loading is the main influencing factor for rapid accumulation of Ue
while the change in confining pressure is not enough tocause a large change in Ue.Axial load is the primary factor influencingengineering disasters. Furthermore
there is a significant negative correlationbetween rock damage variable and confining pressure. The larger the confiningpressure is
the smaller the Ue release ratio of rock is
and the smaller the rockdamage is. Confiningpressure restraint effectively enhances the energy storage capacity of rock andinhibits the dissipation and release of rock energy.