<b>Study on mechanical behavior of anchored fractured sandstone under triaxial unloading disturbance</b>

研究裂缝砂岩在开挖卸荷作用和扰动后的力学响应和破坏模式，以及锚杆对裂缝岩体的锚固作用。利用RMT-150B系统，进行三轴载荷-卸载和单轴重载试验，以评估峰值强度、变形特性和裂纹发展。此外，采用PFC3D离散单元建模来分析细观尺度上的微裂纹萌生和扩展。结果表明，尽管锚固和未锚固的试样在卸载和重载过程中表现出相似的应力-应变曲线阶段，但随着围压的降低，未锚固的试样表现出更大的波动并经历更早的失效。相比之下，锚固试样呈现出更平滑的应力-应变曲线、增强的卸载公差、更少的强度损失、更慢的应变减少和更高的弹性模量。非锚固试件的破坏是通过剪切穿透突然发生的，而锚固试样则经历更渐进的破坏，其特征是拉伸-剪切联合损伤，这归因于锚杆的加固作用。数值模拟进一步证实，锚杆通过改善应力传递和限制裂纹扩展来增强抗扰动能力并改变破坏模式。研究结果为工程应用中卸荷条件下岩体支护系统的设计提供了宝贵的见解。This study investigates the mechanical response and failure mode of fractured sandstone under excavation unloading and disturbance, as well as the anchoring effect of rock bolts on fractured rock masses. The RMT-150B system was utilized to conduct triaxial load-unloading and uniaxial overload tests, aiming to evaluate peak strength, deformation characteristics and crack evolution. Additionally, PFC3D discrete element modeling was adopted to analyze the initiation and propagation of microcracks at the mesoscopic scale. The results demonstrate that both anchored and unanchored specimens exhibit similar stress-strain curve stages during the unloading and reloading processes. However, as confining pressure decreases, unanchored specimens display greater fluctuations and undergo earlier failure. In contrast, anchored specimens feature smoother stress-strain curves, enhanced unloading tolerance, less strength loss, slower strain reduction, and higher elastic modulus. The failure of unanchored specimens occurs abruptly through shear penetration, while anchored specimens experience more gradual failure characterized by tensile-shear combined damage, which is attributed to the reinforcement effect of the bolts. Numerical simulations further confirm that rock bolts enhance anti-disturbance capacity and alter failure modes by improving stress transfer and restricting crack propagation. The findings of this study offer valuable insights for the design of rock mass support systems under unloading conditions in engineering practice.