阿公店水庫越域引水路工程泥岩隧道之設計

阿公店水庫位於高雄縣燕巢鄉境,係以防洪為主並兼具灌溉及公共給水之多目標水庫,惟因庫區淤積情況嚴重,為恢復水庫原有功能並達水資源永續利用之目的,經核定辦理"阿公店水庫更新工程計畫",採台灣首創排潤蓄清之空庫防淤操作,輔以越域引水路導引旗山溪潔淨水源蓄存運用,以同時解決水庫防洪、淤積及給水問题於一舉。隧道基於水理及施工性考量採4.0m内徑2R-3R-3R之正馬蹄型斷面,隧道開挖主要可能遭遇問題包括擠壓破壞及砂岩夾層蕴藏地下水狀況,由於泥岩隧道岩體分類及支撐設計不盡適用CSIR-RMR及NGI-Q值之經驗設計法則,遂採近似Terzaghi之岩壓估算方式,輔以數值分析法計算隧道變形與岩體-支撐之應力,俾檢核支撐設計之適用性,施工期間並彙整監測资料進行反算分析回饑設計,以期達兼顧安全與經濟之合理設計。考量儘早有效抑制隧道岩體擠壓及潛變變形,確保隧道長期之穩定性,並可維護洞内施工動綜提升施工效率,隧道仰拱設計以預鑄混凝土版進行斷面支撐閉合。

DESIGN OF MUDSTONE TUNNEL FOR TRANSBASIN WATERWAY OF AKUNGTIEN RESERVOIR RENOVATION AND IMPROVEMENT PROJECT

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.