(1. Work Safety Key Laboratory on Prevention and Control of Gas and Roof Disasters for Southern Coal Mines，Hunan University of Science and Technology，Xiangtan，Hunan 411201，China；2. Hunan Provincial Key Laboratory of Safe Mining Techniques of Coal Mines，Hunan University of Science and Technology，Xiangtan，Hunan 411201，China；3. School of Resources and Safety Engineering，Central South University，Changsha，Hunan 411803，China；4. School of Resource Environment and
Safety Engineering，Hunan University of Science and Technology，Xiangtan，Hunan 411201，China)
Abstract：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.
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2017, Vol. 36 
