天生桥二级水电站引水隧洞高外水压力形成机制及排水效果渗流场分析

Analysis on the Mechanism of High External Water Pressure andSeepage Field Around the Water Diversion Tunnel andEvaluation of the Effect of Drainage of Tianshengqiao-ⅡHydropower Station

天生桥二级水电站引水隧洞穿过多条岩溶管道。隧洞在施工期多处发生了大涌水。根据暗河的岩溶水文地质条件，分析了高外水压力形成机制；并进行平面渗流场分析，研究设置排水洞后降低外水压力效果。结果表明：设置排水洞后外水压力大大降低．目前，排水洞及其支洞已戳住部分暗河水流，排水效果明显。证明设排水洞是降低外水压力的有效措施。

The diversion tunnels of Tianshengqiao-Ⅱ hydropower station traverses many undergroundkarst rivers. During construction large quantity of karst pipe water gushed into the tunnels. According to hydrogeological condition of the karst rivers, the mechanism of high external water pressure is analysed. Two dimensional seepage field is studied to evaluate the effect of lowering the pressure acting on the lining of the diversiontunnels by using a drainage tunnel. Research shows that with a drainage tunnel the external water pressure acting on the lining of the diversion tunnels is greatly reduced. Now a drainage tunnel and its branch tunnels todrain the karst groundwater are designed and the drainage effect is very obvious. Engineering practice has verified that using a drainage tunnel is an effectual measure to lower the external water pressure.