MONITORING BASED EMERGENCY REINFORCEMENT DESIGN FOR DIVERSION TUNNEL OF MING TOMBS PUMPED-STORAGE STATION IN BEIJING

When the diversion tunnel of Ming Tombs pumped storage station in Beijing passed through the fragmented rock mass, landslip happened in the early stage of excavation because of bad geological conditions. Displacement monitoring was performed in time after landslip. The monitored results showed that support structure composed of anchoring shotcrete with wire mesh and steel arch frame used by the original design had great deformation, especially in the side walls. According to the monitored results, supporting scheme for the diversion tunnel was modified significantly. For example, steel arch frames and reinforced bars for the wire mesh were increased. Sprayed concrete was thickened. The inverted arch was added for the tunnel floor. After the above measures were constructed, the displacement of the tunnel has decreased and the deformation has stabilized. The displacement and deformation have reached the design and operation requirements. The successful design illustrates that the monitoring during construction for design change is very important under complicated engineering geologic conditions. Design of other tunnels can draw lessons from this case study.