Abstract:

The headrace tunnel of Bihai hydropower project penetrates the metamorphic rock formation in eastern Taiwan. It is aligned along the right side of HoPing River in a steep and mountainous terrain. The condition for access road is extremely bad. Before access road could be reached, heavy lift helicopter served as the main transportation role, for catching up the master schedule, to supply the material, personnel, and machines, etc. The net diameter of the 6.5 km long headrace tunnel is only 2.7 m. It limits the design and construction. Taipower chose TBM as the main measure to reduce the construction time. But the original contractor failed due to encountering shear zone with gushing water. TBM got stuck, and failed to release. Taipower changed the contractor, and made a new decision to use traditional drill and blast method instead. The new contractor removed the TBM in pieces and breakthrough the tunnel on schedule. The most successful countermeasures include dealing with gushing water with large diameter drainage pipes and adopting needle beam steel form, etc. The lining speed is almost the fastest record in Taiwan's hydropower projects.

Key words: headrace tunnel, shear zone, lining, needle beam