Research methods for excavation face stability in shield tunneling are deterministic methods at present. In order to account the variability of soil parameters

reliability method to assess tunnel excavation face stability is proposed. Limit support pressure at excavation face of shield tunneling is studied with numerical simulation. Limit support pressures with different soil parameter samples are forecasted by BP neural network. Then the probability distribution of them is gained. Principle of determining the earth pressure during tunnel excavation by use of earth pressure balance shield machine is discussed theoretically and practically. Limit state equation of excavation face stability in shield tunneling is established. Excavation face stability is calculated with reliability method. The work not only can assess excavation face stability rationally

but also is significance to determine the support pressure scientifically.