Mechanical response, deformation behaviour and permeability evolution of surrounding rock under unloading conditions are of significant importance in rock engineering activities. In this research, triaxial experiments of sandstone subjected to different initial confining pressures and unloading rates under fixed axial stress were conducted. The results showed that sandstones experienced shear dilatancy before failure. However, the dilatancy factor did not decrease with increasing confining pressure, i.e. the dilatancy behaviour was not suppressed, which contradicted the phenomenon under increasing axial stress. The crack density also increased with increasing initial confining pressure. Furthermore, the normalized permeability was positively correlated with unloading rates. The sandstone permeability was closely related to the shear dilatancy behaviour. In the accelerated dilatancy stage, the relationship between normalized permeability and volumetric strain was linear at low unloading rates and nonlinear at high unloading rates. The linear/nonlinear relationship between them can directly affect the temporality of respective mutation, so as to guide the prevention of geological disasters at different excavations rates.

卸荷条件下围岩的力学响应，变形行为和渗透率演化在岩石工程活动中具有重要意义。在这项研究中，进行了在固定轴向应力下砂岩在不同初始围压和卸载速率下的三轴试验。结果表明，砂岩在破坏前经历了剪胀性。然而，剪胀系数并没有随着围压的增加而减小，即剪胀行为没有被抑制，这与轴向应力增加时的现象相矛盾。裂纹密度也随着初始围压的增加而增加。此外，归一化渗透率与卸荷率正相关。砂岩渗透率与剪胀特性密切相关。在加速剪胀阶段，归一化渗透率与体积应变之间的关系在低卸载速率下为线性，而在高卸载速率下为非线性。它们之间的线性/非线性关系可以直接影响各个突变的时间性，从而指导不同开挖速率下地质灾害的预防。