THDC India Limited, Rishikesh, Uttarakhand, India
Online published on 11 November, 2021.
Vishnugad Pipalkoti Hydro Electric Project (VPHEP) is a run of the river scheme, located on river Alaknanda, spanning between Helong and Birahi Villages in Chamoli district of Uttarakhand, india. The Project envisages construction of 65m high Concrete Gravity Dam, three nos. underground Desilting Chambers of 390m length each, 13.4 km long circular Head Race Tunnel (HRT) of 8.8 m finished diameter (12 km by double shield Tunnel Boring Machine-TBM) etc. In order to facilitate the start of excavation of HRT through TBM, an entry adit of diameter 9.95m and a chamber of diameter 12 m for launching the TBM are being constructed through huge deposits of River Borne Material (RBM) and slope wash material (debris). Construction of this large adit and large launching chamber by non-blasting, pre-strengthening and multiple drifting methods etc. through RBM is a unique example of engineering in the Himalayan region. Challenges during execution intensified in monsoon season due to massive water seepage laden with silt (being the RBM as tunnelling media) in entry adit to TBM.
This paper briefs about the art of engineering for designing, construction and tackling of complex geological circumstances encountered during construction of such a large adit. The adit 55 m in length, part of which will act as launching chamber (17.5 m length) for TBM has been constructed successfully.
