为揭示循环荷载下地下工程围岩体孔裂隙扩展及破坏机制，借助于单轴压缩和 CT 扫描， 开展了粉砂岩的等幅循环、逐级一次循环加卸载试验。 研究了循环荷载下粉砂岩应力-应变曲线、 孔裂隙扩展及破坏阶段裂缝产状、规模等演化规律。 结果表明:2 种循环荷载作用下，粉砂岩孔隙 率均呈先减小后增加的总趋势，且致裂循环的孔隙率均发生突变，具有瞬时破裂特征;等幅循环加 卸载下，岩石破坏发生在第 25 次循环加载段，主要依据应变差、累积应变差及其一阶导数将岩样破 坏段裂缝扩展细分为裂缝萌生、裂缝扩展和加速破坏等 3 个阶段;逐级一次循环加卸载下，岩石破 坏发生在第 4 次循环卸载强度低于峰值载荷 1.04 MPa 时，呈现出小幅振荡破坏特征，主要依据单 峰波动应力振幅、频率、应变差、累积应变差及其一阶导数将岩样破坏段裂缝扩展细分为裂缝萌生、 裂缝快速扩展、裂缝扩展亚稳态、裂缝再生和加速破坏等 5 个阶段。 按应力-应变曲线形态，小幅 振荡破坏可细分为往复式、滞回环式波动，应力振幅、波动频率特征分析可见清晰的应力调整过程。 岩样原始孔裂隙分布状态对其致裂部位及破坏形式起主控作用。 2 种循环荷载作用下，岩样破裂 均以剪切破裂为主，并次生了张性破裂。 卸载段回弹和扩容效应是出现小幅振荡破坏的主要原因。

In order to reveal the pore fracture propagation and failure mechanism of underground engineering surround⁃ ing rock under cyclic loads，the uniaxial compression and CT scanning were used to carry out constant amplitude cyclic loading and unloading and stepwise linear cyclic loading and unloading tests on siltite. The stress⁃strain curves of siltite，the propagation of pores and fractures，and the occurrence and scale of fractures in the failure stage are studied under cyclic loading and unloading. The results show that the siltite porosity decreases first and then increases under two kinds of cyclic loads，and the porosity of fracture cycle changes suddenly，which has the characteristics of in⁃ stantaneous fracture. Under the constant amplitude cyclic loading and unloading，rock failure occurs in the 25th cyclic loading section， and according to the strain difference， the cumulative strain difference and its first derivative mainly，the fracture propagation in the failure stage of rock samples is subdivided into three stages: fracture initiation， fracture propagation，and accelerated failure. Under the stepwise lineal cyclic loading and unloading，the rock failure occurs in the 4th cyclic unloading section，and presents the characteristics of low⁃amplitude oscillation failure when the strength is lower than the peak load of 1.04 MPa. According to the unimodal fluctuant stress amplitude，frequency， strain difference，cumulative strain difference and its first derivative mainly，the fracture propagation in the failure stage of rock samples is subdivided into five stages: fracture initiation，rapid fracture propagation，metastable fracture propa⁃ gation，fracture regeneration，and accelerated failure. According to the form of stress⁃strain curve，the low⁃amplitude os⁃ cillation failure can be subdivided into a reciprocating cyclic wave and a hysteretic cyclic wave，and the analysis of stress amplitude and wave frequency shows a clear stress adjustment process. The distribution of original pores and fractures of the rock samples plays a major role in controlling the fracture location and failure form. Under the action of two kinds of cyclic loads，the fracture of rock samples is mainly shear fracture and secondary tensile fracture. The rebound and dilatancy effect of the unloading section are the main causes of low⁃amplitude oscillation failure.