Sediment Sluice Tunnel of Zengwen Reservoir and construction of section with huge underground excavation adjacent to neighboring slope

摘要: Abstract To mitigate severe and worsening siltation, a series of management improvement measures have been carried out at the Zengwen Reservoir. The Sediment Sluice Tunnel, built in mountain to left dam, is crucial project prevent inflows with high sediment concentrations that are caused by heavy rain, slowing siltation extend service life reservoir. tunnel has length 1220.3 m, an elevation 175.0 m its intake 103.5 m outlet. designed maximum flow velocity 30 m/s. A huge underground excavation (1058 m2) was conducted construct energy dissipation pool connected twin-bore outlet tunnels were constructed adjacent neighboring slope solve problem hinterland limitation scouring on opposite river bank. During construction tunnels, middle wall between these suffered from overstress support many mutual locked bolts broke successively, causing major emergency. Fortunately, successively scanned LiDAR point clouds provide not only comprehensive displacements rock surrounding associated variation spatiotemporal deformation patterns during tunneling, but also geometric related characteristics discontinuity sets rock, including attitude, spacing persistency bedding two joint sets. set (J2), had poor persistence per results geological investigation performed design stage, disturbed successive excavations tunnels. mobilization shear displacement J2 leaded increase reduction strength, weakening whole mass wall. Such excavation-induced set, accounting for breaking wall, can be hardly determined conventional numerical simulation. Additional installed perpendicular suppress soon after mechanism understood, mitigating crisis effectively.