Abstract
A small-diameter tunnel boring machine was used for the excavation of a headrace tunnel (excavated diameter 2.6m, length approximately 1145 m) at a small hydro project for the Electric Power Development Co. Ltd. Based on detailed geological investigations, the rock mass was classified comprehensively into five levels according to hardness of the rock, degree of weathering, spacing of cracks, etc. In addition, lateral loading tests in boreholes, seismic tests and laboratory tests on rock cores were carried out. The modulus of deformation, seismic wave velocity, thickness of loosened zone and the uniaxial compressive strength of the rock were obtained from the results of these tests. Additionally, the mechanical performance of the tunnel boring machine during excavation was recorded. Thrust, torque, excavation rate and abrasion loss from the cutters were examined in detail for each excavation section. It was found that the performance characteristics of the machine have a close relation with the rock mass classes. Studies were also undertaken to evaluate the excavation cost as a function of the geological conditions when using the tunnel boring machine.
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