Water ingress in long hard rock TBM tunnels

David Lees

The 15 km headrace tunnel for the Uma Oya project in Sri Lanka was excavated by double shield TBM and intersected large quantities of water. The study of this project with regards to better understanding the effects of the tunnel on the hydrogeology of the area, identifying relevant in-tunnel investigation techniques, and developing better pre-excavation and post excavation grouting systems is relevant to other long hard rock TBM projects.

The presentation will address why we need to limit the water ingress into tunnels under construction with regards to the potential effect on the environment with dewatering of surface and near surface aquifers, the effect on the construction and its schedule, and the methods available for prediction and control of ground water during tunnel excavation.

Examples from other projects around the world including past completed projects, projects under construction and future planned projects, detailing how such hazards have been or will be treated, will also be presented.

Engineers Australia members participating in AGS technical sessions can record attendance on their personal CPD logs. Members should refer to Engineers Australia CPD policy for details on CPD types, requirements and auditing guidelines.