Face failure in homogeneous and stratified soft ground: Theoretical and experimental approaches on 1g EPBS reduced scale model

Mechanisms of face collapse and face blow-out of tunnels driven in soft grounds with pressurized shield tunnel boring machine are studied. Results presented are issued from several tests carried out with an original laboratory reduced-scale model of earth pressure balanced shield (EPBS). The failure kinematics and limit face pressures in homogeneous purely frictional or cohesive–frictional soils, as well as in stratified soils (two or three-layered soils) are presented and analyzed. Comparisons of these experimental results with the predictions from yield design theory are discussed.

► Tests are carried out with an original EPBS reduced-scale physical model.
► Experimental results are compared with yield design theory.
► Face collapse: agreement in cohesive frictional but not in purely frictional soil.
► New mechanisms in stratified soils are exhibited.
► Low relevance of the theoretical model on blow-out failure.