黄金坪水电站大断面尾水隧洞结构安全性研究

依托黄金坪水电站尾水隧洞工程,采用数值模拟、现场监测的手段进行了深埋大断面尾水隧洞开挖结构安全研究。研究结果表明:将隧洞断面划分为4层开挖,顶层采用导坑扩挖法,先开挖中部导坑,再向两侧进行刷扩处理,因刷掉的是围岩松动圈外圈的低应力松散带,避免了扰动深部围岩,有利于结构安全;大断面尾水隧洞在分层开挖、支护过程中,围岩最大拉应力为0.86 MPa、最大压应力为6.9 MPa,支护结构最大拉应力为0.6 MPa、最大压应力为5.0 MPa,均远小于允许应力而且不会发生岩爆,围岩和隧洞支护体系在开挖、支护完成后逐步达到稳定状态;围岩多点位移计的现场监控量测结果验证了数值计算结果的正确性,研究方法可为类似工程提供参考。

Case Study on Structural Safety of Large Cross-section Tailrace Tunnel of Huangjinping Hydropower Station

In the paper, the structural safety of the deeply-buried large cross-section tailrace tunnel of Huangjinping hyd ropower station is evaluated by means of numerical simulation and field monitoring. The result of this study shows ： The tunnel is excavated in four benches, and Bench I is excavated by pilot tunneling method, i. e. , the pilot is excavated before enlarging excavation is made. In this way, the disturbance to the deep surrounding rock is avoided, because the loose surrounding rock with low stress at the outer ring of the surrounding rock is excavated in the enlarging excavation. Therefore, the excavation method adopted is favorable for the structural safety of the tailrace tunnel. In the process of the excavation and supporting of the large cross-section tailrace tunnel, the maximum tensile stress and the maximum com- pressive stress of the surrounding rock are 0.86 MPa and 6.9 MPa respectively, and the maximum tensile stress and the maximum compressive stress of the supporting structure are 0.6 MPa and 5.0 MPa respectively. All of the above-men- tioned values are far less than the allowable stress values, and rock burst would not happen. The surrounding rock and the supporting structure reach stable gradually after the excavation and supporting are finished. The field monitoring re- suits obtained by multi-point displacement gauges verifies the accuracy of the numerical results. The research method de- scribed in the paper can provide reference for similar projects in the future.