Study on cracking process and influencing factors of reinforced concrete lining in high-pressure tunnels

To effectively prevent severe cracking and leakage in the reinforced concrete linings under high water pressure， it is essential to investigate the cracking process and its influencing factors for the purpose of guiding the crack-limiting design of pressure tunnels and controlling crack width. Based on the theory for coupling between stress and seepage flow in the the pores and fractures， a discrete element approach for seepage-stress-cracking coupling analysis of the dual medium of pressure tunnels was established. The approach was validated using the results from model tests of pressure tunnels. Subsequently， a numerical simulation of the filling and emptying process of large-diameter high-pressure tunnels was conducted. The characteristics of lining crack evolution during the process was analyzed， and the effects of factors such as the permeability coefficient of the surrounding rock， lining thickness， rebar diameter， and the number of cracks on the crack width in the lining was studied. The rationality of the existing crack control criteria was discussed. The results indicate that the method established in this paper can effectively reflect the results of pressure tunnel model tests and the operational behaviors. The crack width in the lining is positively correlated with the filling water pressure. Due to the increased external water pressure on the lining after cracking and the separation between the lining and the surrounding rock， the crack propagation pattern undergoes a complex process. The total crack width in the lining is directly proportional to the permeability coefficient of the surrounding rock， lining thickness， and the number of cracks. The findings provide technical support and theoretical reference for the crack-limiting design of the permeable linings of high-head pressure tunnels.