Model Study of Tunnel Prereinforcement

Physical models were designed for the investigation of two prereinforcement systems: (1) Reinforcing far ahead of the main excavation; and (2)spiling reinforcement ahead of the face. In both cases, the use of reinforcement was responsible for permanently stabilizing an otherwise unstable opening. Data from the physical models were used to calibrate a numerical model from which additional information on long-term behavior, methods to account for the capacity of a prereinforcement system, and the mechanisms involved were ascertained. These studies indicated that prereinforcement can stabilize a rock mass effectively as it reduces deformations and thereby deterioration due to strain softening, provides rock mass confinement leading to increased available strength, and maintains rock arch continuity allowing for increased tangential stress in the immediate vicinity of the opening.