Water hammer pressure and limit support pressure on shield excavation face under high water pressure

Under high water pressure, water hammer pressure induced by pressurized water flow in soil may cause shield excavation face collapse. A theoretical model for calculating water hammer pressure on underwater shield excavation faces is deduced. By optimizing E. LECA’s failure mode for shield-tunnelling faces using upper-bound limit analysis, an upper-bound solution for the limit support pressure of a three-dimensional shield tunnel face is derived. This solution is compared with the water hammer pressure formula, and the critical water surface height (hw) under different C/D is solved graphically. Results show that when the water surface is low, water hammer effects can be ignored. As water surface height exceeds hw, water hammer impact increases. For identical soil parameters, hw increases with C/D, exhibiting a linear relationship. This supports safer design of underwater shield tunnelling.