Behavior of Pressure Tunnels and Guidelines for Liner Design

Numerous cases of pressure‐tunnel failures have occurred in recently commissioned projects. The cost of the remedial measures, particularly the lost revenue during the time taken for the implementation of these measures, is significant. This paper presents a framework to identify and evaluate the variables that control tunnel behavior and thus determine the key decisions made in the design of a pressure tunnel. An approach is also given for incorporating the hydraulic and mechanical liner‐ground interaction in the evaluation of the water tightness of various types of liners under operating conditions as well as for evaluating the capability of these liners to control the pore‐water pressure in the surrounding rock mass. This approach also permits an evaluation of potential benefits derived from consolidation grouting of the rock mass surrounding the tunnel. Finally, specific liner design recommendations and guidelines are given to accommodate a wide combination of rock mass characteristics, topography, ground‐water levels, and operating conditions.