Abstract Brittle rock mass failures due to geostress release (rock burst and spalling, etc.) and caused by structural plane stress (surrounding rock relaxation, shotcrete spalling and crown collapse, etc.) are very common during underground cavern excavation. Taking the underground cavern group of tailrace connection pipes at the left bank of the Baihetan hydropower station as an example, and based on a statistic and analysis of site survey results, it studied the rock failure mechanism due to geostress release by means of 500 μm microscopic observation and the indoor uniaxial compression test. Rock failure mechanism caused by structural plane stress was also studied by numerical simulation and in-hole video, and some corresponding countermeasures were proposed. The research indicates that the brittle rock mass with good integrity (grade Ⅱ) has certain plasticity, it is prone to inducing shear compression failure and forming a failure plane with a small angle relative to force direction after load release due to cavern excavation, plastic potential energy releases along fracture plane and then causes spalling of thin layer or rock burst; the rock mass with poor integrity (grade Ⅲ) has characteristics of high lithological strength and low rock mass strength due to presence of joints and dislocation interfaces; micro-cracks of rock mass gradually spread and connect each other to form mutual cutting structural planes, and it develops towards further depth of rock mass until stress releases completely under the effect of high geostress; it is inclined to causing collapse due to the vibration effect of cavern blasting, the failure develops from outside to inside and is characterized by time-efficiency from the macroscopic view.
Abstract：
Brittle rock mass failures due to geostress release (rock burst and spalling, etc.) and caused by structural plane stress (surrounding rock relaxation, shotcrete spalling and crown collapse, etc.) are very common during underground cavern excavation. Taking the underground cavern group of tailrace connection pipes at the left bank of the Baihetan hydropower station as an example, and based on a statistic and analysis of site survey results, it studied the rock failure mechanism due to geostress release by means of 500 μm microscopic observation and the indoor uniaxial compression test. Rock failure mechanism caused by structural plane stress was also studied by numerical simulation and in-hole video, and some corresponding countermeasures were proposed. The research indicates that the brittle rock mass with good integrity (grade Ⅱ) has certain plasticity, it is prone to inducing shear compression failure and forming a failure plane with a small angle relative to force direction after load release due to cavern excavation, plastic potential energy releases along fracture plane and then causes spalling of thin layer or rock burst; the rock mass with poor integrity (grade Ⅲ) has characteristics of high lithological strength and low rock mass strength due to presence of joints and dislocation interfaces; micro-cracks of rock mass gradually spread and connect each other to form mutual cutting structural planes, and it develops towards further depth of rock mass until stress releases completely under the effect of high geostress; it is inclined to causing collapse due to the vibration effect of cavern blasting, the failure develops from outside to inside and is characterized by time-efficiency from the macroscopic view.
SUN Huixiang
.On Failure Mechanism of Surrounding Rocks of the Deep-buried Underground Cavern Group under High Geostress and Its Countermeasures[J] MODERN TUNNELLING TECHNOLOGY, 2019,V56(3): 8-17
2019, Vol. 56 