A study on the excavation face failure of pressurized slurry shield.

• The pressure fluctuation occurred during the tunnel construction. • Numerical simulation and experiments are both carried out to analyze the causes. • The breakdown of the filter cake is the main cause of the pressure fluctuations. • Compressed air breaks through filter cake, which causes pressure fluctuations. The Wuhan Metro Line 8 Crossing River Tunnel Project suffered manifest pressure fluctuations when opening the excavation chamber of the slurry shield. In this paper, numerical simulation and air pressure test are both carried out to analyze the causes of the pressure fluctuation. The analysis results show that the air pressure applied on the excavation face during the opening of chamber lies in the safe region, excluding the possibilities of active and/or passive excavation face failures. Then, calculated by empirical formula, the pressure on site is lower than the hydraulic fracture pressure, which means the pressure fluctuation is not related to the hydraulic fracture. At last, by air pressure tests, the break through pressure of the filter cake is found much smaller than the air pressure on site. Therefore, it is concluded in this paper that the quality of the filter cake does not meet the design standard, and the breakdown of the filter cake is the main cause of the observed pressure fluctuations on the excavation face. Furthermore, the mechanism of filter cake breakdown is investigated experimentally. [ABSTRACT FROM AUTHOR]