Due to the coexistence of the thin layered marbleized dolomite rock mass and a major fault ( F3 ) in the entrance segment of the No. 3 and No. 4 diversion tunnels at right bank of Wudongde Hydropower Station, the geological condition is poor. Besides, due to large excavation cross-section, high side wall and thin separate wall for the two tunnels, collapse is prone to oc-cur during tunneling. The two excavation schemes of Ⅱand Ⅲ layers, namely the left excavation first and right excavation sec-ond, the right excavation first and left excavation second, in the entrance segment under the existing supporting scheme were compared through numerical simulation. The relaxation depth, measured displacement, the maximal and the minimum principal stress, and the displacement increment of the monitoring points of the selected typical sections were determined. It was shown that the scheme of left excavation first and right exaction second is better. Meanwhile, as affected by the fault andⅤtype rock, the separate wall between No. 3 and No. 4 diversion tunnels is in an extremely unstable situation, so the penetrating anchors is necessary during construction. The in-situ practice showed that stability of the rock mass would be guaranteed as the scheme of left excavation first and right excaction second was adopted and the penetrating anchors were applied.%乌东德水电站右岸3、4号导流洞进口段为薄层的大理岩化白云岩,并且存在大断层,地质条件较差。同时,由于导流洞施工具有开挖断面大、边墙高及中隔墙薄等特点,隧洞开挖过程中存在局部垮塌的隐患。在该区域选取了4个典型断面,借助数值模拟手段,在既有的支护方案下对比了导流洞进口段Ⅱ、Ⅲ层先左侧后右侧及先右侧后左侧开挖方式下各典型断面的松弛深度、位移、最大主应力及最小主应力的分布情况,同时给出了两种开挖方式下监测点处的位移增量情况。分析结果表明,先左后右的开挖方案更优。同时,受断层及Ⅴ类围岩的影响,3、4号导流洞中隔墙区域处于极不稳定的状态,应施加对穿锚索支护。现场开挖实践表明,采用先左后右的开挖方案并在3、4号导流洞中隔墙区域进行对穿锚索的加强支护保证了围岩的稳定性。
展开▼
