南桠河三级水电站的地下洞室,包括引水隧洞、调压井、斜井式压力管道和施工支洞,全长约十公里。开挖直径一般为5.5至6.5米(调压井为17.5米)。洞室埋深在山脊部分多大于400米;冲沟切割处仅27.5至64.0米。沿线均属早震旦系花岗岩体。由于水电站位于“川滇南北向构造带”上,又介于区域大断裂——南北向楂罗断裂和北西向石棉断裂之间。围岩因构造变动的影响受到强烈的破坏,断裂纵横交错,岩脉穿插繁杂,致使岩体完整性较差。在洞室开挖过程中,主体工程上仅大规模坍方就有十六处之多(见图1)。客观上因围岩整体 The underground cavern of Nanyanghe III hydropower station includes diversion tunnel, surge shaft, inclined shaft pressure pipe and construction branch hole, which is about 10 kilometers in length. Excavation diameter is generally 5.5 to 6.5 meters (17.5 meters surge tank). Depth of burial depth in the ridge part of more than 400 meters; gutter cutting only 27.5 to 64.0 meters. Along the line are early Sinian granite body. As the hydropower station is located in the “Sichuan-Yunnan-North-South tectonic belt”, it is also between the regional major faults - the north-south hawthorn fault and the northwest-west asbestos fault. The surrounding rock is strongly destroyed due to the tectonic changes. The fractures are criss-crossed in a crisscross pattern, and the dykes are interwoven so that the integrity of the rock mass is poor. In the excavation of the cavern, there are only as many as 16 large-scale collapses in the main project (see Figure 1). Objectively due to the surrounding rock as a whole