| The world-wide use of pressure tunnels and shafts in hydroelectric, water supply, and sanitary sewer projects has been steadily increasing over the past 25 years. This trend will continue as underground excavation techniques improve and become more economical, and as pumped storage hydroelectric projects become more popular. The magnitudes of the internal pressures of these projects are also increasing.;The review of design procedures was supplemented with an examination of approximately 160 case histories of projects with pressure tunnels and shafts. Particular attention was given to projects where a failure or incident occurred. The case history information has been summarized in the form of tables and discussions, and provides a basis for comparisons between project design and performance.;A review has been made of historical and current design approaches for unlined and lined pressure tunnels and shafts. Particular issues which have been addressed in detail include: adequate confinement of unlined pressurized waterways for the prevention of hydraulic jacking; assessment of leakage potential; layout strategies of tunnels, shafts, and surge facilities, with consideration of constructability; load transfer of internal pressures for steel lined, concrete encased, penstock tunnels and shafts; and the design of steel lined sections for resistance to buckling due to external pressures. Additional topics which have been addressed include: hydraulic roughness of drill and blast and machine excavated waterways; lake taps; plugs; grouting; and drainage. |
