In this study, we investigated the failure process and evolution mechanisms in circular tunnels under a complex stress path of deep in-situ stress + excavation unloading + stress adjustment using a simulation test based on loading first and then drilling (LFTD) mode. This test was performed on cubic sandstone specimens using a true-triaxial testing system combined with a self-developed drilling unloading test device. For comparison, another set of sandstone specimens, similar to the original specimens but with Φ25 mm circular through-holes, were processed to perform another set of simulation tests based on drilling first and then loading (DFTL) mode. Under constant lateral stress, compared with the DFTL test, the initial failure vertical stress was lower, and the surrounding rock was more prone to failure in the LFTD test, indicating that drilling unloading causes damage to the surrounding rock, thereby inducing a strength-weakening effect. Under constant lateral and vertical stresses, sidewall failure in the LFTD test was more severe. The sidewall's initial failure vertical stress difference between the LFTD and DFTL tests increases with increasing lateral stress or initial hydrostatic pressure. The effect of drilling unloading becomes more apparent under a higher initial stress state. Comparing the same types of simulation tests under different stress states, the initial failure vertical stress increases with the lateral stress or initial hydrostatic pressure, inducing a strength-strengthening effect in the surrounding rock. Comparing the strength-strengthening effect caused by increasing the lateral pressure or initial hydrostatic pressure and the strength-weakening effect caused by drilling unloading shows that the strength-strengthening effect is more evident.

本研究采用先加载后钻孔（LFTD）模式模拟试验研究了深地应力+开挖卸荷+应力调整的复杂应力路径下圆形隧道的破坏过程及演化机制。本次试验采用真三轴试验系统结合自主研发的钻井卸荷试验装置对立方砂岩试件进行。为了比较，另一组砂岩标本，与原始标本相似，但具有Φ加工 25 mm 圆形通孔以执行另一组基于先钻孔后加载 (DFTL) 模式的模拟测试。在恒定侧向应力下，与DFTL试验相比，LFTD试验的初始破坏竖向应力较低，围岩更容易发生破坏，说明钻孔卸荷对围岩造成破坏，从而引起强度弱化。影响。在恒定的横向和垂直应力下，LFTD 测试中的侧壁失效更为严重。LFTD 和 DFTL 测试之间的侧壁初始失效垂直应力差随着侧向应力或初始静水压力的增加而增加. 在较高的初始应力状态下，钻井卸荷效果更加明显。对比不同应力状态下的同类型模拟试验，初始破坏竖向应力随着侧向应力或初始静水压力的增加而增加，从而引起围岩强度强化作用。对比增加侧压或初始静水压力引起的强度强化作用和钻井卸荷引起的强度减弱作用，强度强化作用更加明显。