石灰岩孔道试样孔内卸压条件下破坏特征的研究

 为了研究复杂应力环境下岩体工程开挖的影响，设计内压加卸载试验装置，利用内径20 mm、外径49.84 mm的厚壁圆筒石灰岩试样，在RMT–150C岩石力学试验系统进行不同内压条件下的加卸载试验，重点分析了孔内卸压条件下试样的破坏形式产生机制。结果表明：(1) 固定孔压加载时，由于试样孔道内外存在应力差，不能进入延性变形阶段，高围压时有孔压试样的强度明显高于无孔压试样的强度；(2) 孔压卸载对试样造成的损伤较大，卸载孔压后重新加载的试样，其强度低于常规三轴压缩时的孔道试样；卸载破坏时试样内外压差越大，其强度越小，表明围岩发生破坏的根源在于巷道开挖卸载后引起应力差的增加；(3) 固定孔压时，试样多呈现单一的剪切面滑移破坏，而卸载孔压时试样破坏形式都为张拉破坏或者压拉组合破坏，应力路径对孔道试样破坏形式影响较大。研究结果为揭示深埋巷道围岩破坏失稳现象的产生机制提供参考。

Failure characteristics of hollow cylindrical specimens of limestone under hole pressure unloading

A new device was designed to study the failure characteristics of rock in complex stress state under excavation unloading. The hollow cylinder specimens with 49.84 mm in outer diameter and 20 mm in inner diameter were prepared and were tested under loading and unloading conditions on the system RMT–150C. The failure mechanism of the specimens subjected to the hole pressure unloading was discussed in detail. Owing to the existence of the stress difference，the hollow cylinders do not show the ductile behavior under the high confining pressure，the strengths of the hollow cylinders with hole pressures are greater than those of the hollow cylinders with no hole pressure at high confining pressure. The effect of the hole pressure unloading on the damage of hollow cylinder is great. The strengths of the hollow cylinders under the hole pressure unloading are lower than those of the hollow cylinders under the axial loading. The influence of the unloading on the strength is smaller when the stress difference at the failure is large. This indicates that the reason of the failure of the surrounding rock lies in the increase of the stress difference after the excavation unloading. The failure mode of most of the hollow specimens with a certain hole pressure is shearing. However，all specimens under hole pressure unloading conditions present the modes of tensile failure or tensile-shear failure，indicating that the stress paths have the great effect on the failure patterns of the hollow cylinders.