大埋深、高地应力地下洞室群围岩破坏机理及应对措施研究

On Failure Mechanism of Surrounding Rocks of the Deep-buried Underground Cavern Group under High Geostress and Its Countermeasures

地下洞室开挖过程中,脆性围岩应力释放型破坏(岩爆、片帮掉块等)和结构面-应力型破坏(围岩松弛、喷层开裂、顶拱坍塌等)是洞室群围岩破坏常见的主要形式。文章以白鹤滩水电站左岸尾水连接管洞室群为研究对象,结合现场踏勘统计分析,基于500μm显微镜观察、室内岩石力学单轴压缩试验对围岩应力释放型破坏机理进行了研究,基于数值模拟、孔内摄像技术对围岩结构面-应力型破坏机理进行了研究,并分别提出了相应的应对措施。研究表明,完整性较好的脆性围岩(Ⅱ类)具有一定的塑性性能,洞室开挖卸荷后岩体易发生压剪破坏,产生与受力方向呈小夹角的破坏面,塑性势能沿破裂面释放,进而引起薄层掉块或岩爆现象;对于完整性较差的围岩(Ⅲ类),由于节理、错动带等裂隙的存在,多表现为岩性强度高、岩体强度低的性状。围岩微裂纹在高地应力作用下逐渐扩展连通,形成相互切割的结构面,并逐步向岩体深部不断发展,直至应力完全释放,受周边洞室爆破振动影响时易发生坍塌现象,破坏过程在宏观上表现为由表及里并具时效性的特点。

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.