ABSTRACT
The method of tunneling without pressurization involves control of the tunnel free zone stability. An experimental modeling program was carried out to study the behavior of the tunnel free zone during excavation. The reduced-scale model simulated the staged excavation of a circular tunnel at ENTPE, DGCB in Lyon, France. Three soil types were used to investigate influence of soil cohesion on the response of the excavated zone. Horizontal displacements on the circular excavation front were measured using an ultrasonic system to monitor the soil response. Measured displacements included both instantaneous and creep deformations of the excavated front. Conclusions show that the magnitude of tunnel face displacement is a crucial indicator that can be used to predict the outset of tunnel failure as a result of the increase in tunnel excavated length.
