ABSTRACT
Uma Oya Multipurpose Development Project is under construction in Sri Lanka. The headrace Tunnel (HRT) as a water transfer tunnel in this project has already passed 11.5km milestone and is mined in hard rock by TBM. The basic strategy for avoiding damage and negative influence on the surface (environmental problems) due to the water ingress into the tunnel relies on the execution of pre-excavation grouting. This paper reviews, the operation of TBM in headrace tunnel in more detail, focusing on the challenges of excavating through very strong and abrasive quartzite and gneiss, as well as encountering some high inflow of water along the tunnel. Furthermore, the water control procedures including Pre-Excavation Grouting (PEG) and Post Grouting (PG) methods to reduce the ground water ingress done in HRT are described.
