Few theoretical methods and experimental data exist for the analysis of tunnel-face stability in cohesionless soils. The present paper addresses a series of practical questions by using centrifugal-model tests. The values of limit internal-support pressures are given for various conditions (density of the sand, position of the tunnel with respect to the ground surface). These values are shown to be low as predicted by the latest limit-calculation models and collapse is shown to be sudden. The geometry of the failure zone is depicted for different embedment depths. The initial mechanism appears to be of a bulk shape with a limited extent in front of the face. The presence of a short unlined length of tunnel at the face is also investigated. Data are presented about its effect on the failure mechanism, on the limit pressure, and on stress transfer onto the tunnel lining at collapse. The results obtained in the model tests are in general agreement with present knowledge of full-scale situations.
