Abstract：The Akungtien Reservoir，located at upstream of Akungtien Creek，Yenchao Hsiang，Kaohsiung County，is a multipurpose reservoir，with functions of flood prevention，irrigation and public water supply. The reservoir suffered severe sedimentation since its completion. The A-kung-tien Reservoir Renovation and Improvement Project adopts an original measure of reservoir evacuating operation by spilling turbid flood and storing clear water，and diverting clear water from Chishan Creek to solve the problems and fulfill the functions. On account of hydraulic properties and construction capacities，the transbasin tunnels are designed with 2R-3R-3R U-shaped cross-section and 4 m in inner diameter. The major problems in tunnel excavation stage may be squeezing failure and encountering sandstone strata rich in groundwater. Because the experience design method based on CSIR-RMR and NGI-Q systems is not quite suitable in rock mass classification and support design of mudstone tunnels，Terzaghi's rock loading concept combined with numerical analysis on deformation-support stress relation is adopted to examine the applicability of support design. In construction stage，feedback analysis with tunnel monitoring data and on-going design are performed to achieve a reasonable，economical，and safety design of tunnel supports. The tunnel invert is closed by installing precast concrete plate to effectively suppress the deformation of rock masses caused by squeezing and creeping and to ensure long-term stability of tunnel support.
2004, Vol. 23 
