The headrace tunnel of Shihlin hydropower project extend about 5500 m long from the intake gate shaft to the surge tank for leading flow into the Liyutan Reservoir. Before releasing into the reservoir, the headwater of the project, having 284 m head will be fully utilized for power generation. The tunnel will be of a concrete lined pressure type with an inner diameter of 3.5 m. The upstream stretch, about 1.2 km as measured from the intake, passes through the Shihlin anticline geological structural formation and coal deposits. Accordingly, the conventional construction method, drilling and blasting (D&B) method has been selected for tunnel excavation from intake in the downstream direction. This selection is based on the consideration that the fault, shear and gas containing zones, can be safely and quickly passed with the D&B method. Meanwhile, the tunnel boring machine (TBM) method has been selected to excavate the remaining portion of the tunnel from the surge tank in the upstream direction toward the intake for shortening excavation time of the tunnel construction.
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