侧向卸荷条件下冻结砂岩变形特性

Characteristics of deformation properties of frozen sandstone under lateral unloading condition

新庄煤矿立井采用冻结法施工技术,在井筒开挖的过程中,由于侧向卸荷作用导致围岩产生卸荷变形。从新庄煤矿立井现场采集白垩系中粒砂岩,对加工后的岩样进行饱水处理,然后利用GCTS电液伺服控制高低温高压岩石三轴测试系统进行冻结(-10℃)条件下的恒轴压、卸围压三轴试验,模拟在井筒开挖过程中围岩的应力变化路径,探索冻结砂岩的变形特性。研究表明:侧向卸荷条件下冻结砂岩表现出弹-脆性特征,轴向表现为压缩变形,径向表现为膨胀变形,径向变形量约为轴向变形量的2倍;当卸荷速率一定时,岩样的卸荷变形随初始围压的增大而增大,尤其是径向变形最为显著,这可能与卸荷回弹变形及岩样内部聚集的能量大小有关;围压卸荷到同一应力水平时,高卸荷速率下岩样的卸荷变形量较小,而变形速率较大;卸荷作用导致岩样变形模量减小,横向应变与纵向应变之比增大,卸荷速率越小,初始围压越大,应变之比变化越大。

The freezing method is adopted in Xinzhuang coal mine, and during the process of shaft excavation lateral, unloading leads to the unloading deformation of surrounding rock. The cretaceous media-grain sandstone is collected from Xinzhuang coal mine, and the samples are processed into saturated states. Then, the constant-axial compression and unloading confining pressure triaxial tests are carried out under freezing（-10 ℃） conditions using GCTS servo-controlled high-low temperature and high-pressure triaxial rock testing system. The stress change path of surrounding rock is simulated in the process of shaft excavation, and the deformation characteristics of frozen sandstone are explored. The results show that under the condition of lateral unloading, the frozen sandstone shows obvious elastic-brittle characteristics. There has compression deformation in the axial direction, but expansion deformation in the radial direction. Moreover, the radial deformation is approximately two times larger than the axial deformation. With the same unloading rate, the unloading deformation of rock specimens increases with the increase of initial unloading confining pressure, and especially the radial deformation is the most significant. This may be related to the unloading rebound deformation and the amount of energy accumulates within the sample. When the confining pressure is unloaded to the same stress level, the unloading deformation of rock specimens is small, and the deformation rate is greater under high unloading rate. The deformation modulus of rock samples decrease in the unloading process, but the ratio of lateral strain to longitudinal strain change increases. The smaller the unloading rate is, the larger the initial unloading confining pressure is, and the greater the variation of deformation modulus is.