DESIGN, CONSTRUCTION, AND OPERATION OF UNLINED PRESSURE TUNNELS: SUGGESTIONS FOR GOOD INDUSTRY PRACTICE

摘要

The design, construction and operation of unlined pressure tunnels for the conveyancernof water requires a comprehensive evaluation of a number of key technicalrnissues including the prevailing geological conditions prior to construction, considerationrnof hydraulic requirements, operations, impact of scour on long term tunnel stability,rnmethod of excavation, evaluation of final lining, maintenance access requirements duringrnoperations, debris accumulation and hydraulic design of rock traps, and an evaluationrnof the encountered geological conditions from detailed mapping during construction.rnWith the continued construction of an increasing amount of unlined pressure tunnelsrnparticularly for hydropower development a number of lessons have been learned overrnthe past few decades regarding the design, construction and operation of unlined pressurerntunnels. The acceptability of unlined pressure tunnels for any given site needs tornconsider environmental impacts and the potential for external influences during operations.rnMany unlined pressure tunnels have been successfully constructed and operatedrnfor decades without any major problems. Some rock environments appear to berncommonly associated with the presence of adverse and dissoluble mineral infillingsrnthat can result with excessive scour that can manifest into significant blockages andrncollapses. The uncertainty associated with the requirements for final tunnel supportrnand lining suggests that risk-sharing contracts offer the best choice to owners to providerna reliable conveyance tunnel for low-risk operations. This paper serves to addressrna number of key technical issues for practitioners and offers suggested guidelines forrngood industry practice.