Managing Geological Complexity in BVC and PAC of Tehri PSP, India - A case study


Tehri hydroelectric project is located on the left bank of River Bhagirathi in the state of Uttarakhand. Tehri Pumped Storage Project (PSP) comprising 4 Nos of reversible pump-turbine units of 250 MW each, involves construction of an underground Machine Hall, Upstream Surge Shaft with Chambers - 3 & 4, a Butterfly Valve Chamber (BVC), a Penstock Assembly Chamber (PAC), the Downstream Surge Shaft with Chamber - 3 & 4, a pair of Tail Race Tunnels (TRTs) and the Outlet structures. Execution of large infrastructure projects cannot be imagined without high- level engineering explorations, the prerequisites to increasing the economic efficiency of capital investments. Prior Estimate of uncertainties and risks involved in the construction process is central to decision making in the underground projects. In such Projects, a significant part of uncertainties results from unknown geological conditions. Timely calculation of risks and action required therein is vital in mitigating geological risks in the underground construction and tunnelling projects. Continuous updating of geological models, readjustment of excavation and support to actual ground conditions are the measures that control all geological risks at the site. In short, adopting appropriate excavation technology, proper sequences, dependable support, monitoring behaviour and auxiliary measures mitigate the geological risks to a great extent.