Abstract: Reasonable support pressure on excavation face is the key to maintaining the tunnel face stable and safe during shield tunnelling construction. In this study, the passive failure mode of excavation face in clay strata, the plastic zone development, and the stratum displacement caused by excessive support pressure are simulated numerically in consideration of soil strength reduction induced by segmented advancing and excavation unloading. In addition, the influences of tunnel depth, tunnel diameter, and soil properties on the limit support pressure are explored. The reasonable range of limit support pressure is given through centrifugal model test. Results are concluded as follows: 1) When support pressure intensifies gradually, the front soil is squeezed into a shovel shape, and in the meantime, a ring plastic zone is formed around the excavation face due to punching and cutting effect. With the distance to excavation surface prolongs, the longitudinal strata displacement in front of excavation face increases but then decreases until stabilizes; whereas the horizontal strata displacement in the deep follows normal distribution.2) The augment of tunnel depth and tunnel diameter would amplify the limit support pressure to different extends. Support pressure is most sensitive to elastic modulus, followed by internal friction angle, Poisson’s ratio and cohesion. The range of passive limit support pressure is recommended to be 1-1.9 times of earth pressure at rest. The results would offer reference for shield tunneling construction control in clay stratum.

Key words: shield tunnelling, clay strata, tunnel excavation face, passive failure, numerical simulation, centrifuge mode test