Abstract: It is difficult to prevent the cracking of the lining of hydraulic tunnels under high water pressure. The key to designing a permeable lining is to determine the stress characteristics and crack control standards of reinforced concrete structures under the loads jointly born by the lining and surrounding rock. Based on the characteristics of crack initiation and propagation in pressure tunnel linings, this study analyzes the engineering applicability of conventional formula calculations and numerical methods to concrete lining cracking, and examines the sensitivity of crack openings to determine the main parameters of lining design. We also compare the results of crack control standard analysis, numerical simulation, and actual measurement, and demonstrate the key to evaluating a crack control standard of the linings. The results show that most of the projects are in normal operation, even though their measured crack openings are often beyond the crack limit standard. The current global crack control standards are too strict, lowering the utilization efficiency of support structure materials. Therefore, new threshold crack opening that is consistent with the real engineering cases should be established. Considering the engineering safety and economic benefits of pressure tunnels, this study suggests that the reasonable reinforcement ratio of concrete linings should be roughly 0.9%, lining thickness roughly 800 mm, and critical crack opening 0.35-0.5 mm.

Key words: pressure tunnel, formula method, numerical simulation, threshold crack opening, reinforcement ratio, lining thickness