Modeling and monitoring in a soft argillaceous shale tunnel

Taking advantage of measurements from an in situ monitoring program and an elastoplastic model using the finite-difference method, this paper simulates and evaluates the deformation and stability of a tunnel in soft argillaceous shale. The elastoplastic model is implemented in FLAC3D program to simulate the deformation and the stress of the soft argillaceous shale during construction. In situ tests performed in the soft argillaceous shale tunnel show that the results from numerical simulations are in good quantitative agreement with the measured in situ data. Results of the simulations also suggest that deformation rate is high during the initial phase of tunnel excavation, compared with the later phase, but the time to reach a steady state remains long. Entire primary support has been undergoing plastic deformation before construction of the secondary lining, which takes the form of so-called “shear yield” from the middle to the bottom of the arch. Some auxiliary measures, especially the anchor, should be applied to enhance stabilization because of the large compressive stress located at the arch springing of the tunnel. The methodology applied in this article can be used to investigate the effect of construction on the performance of tunnels in soft argillaceous shale.