Modelling the deformation of underground excavations in layered rock masses (original) (raw)

Two small-scale models simulating an opening in a flat-lying layered rock mass were manufactured in the laboratory using ilmenite sand and gypsum mixtures and tested on a loading frame until failure. It was observed that the failure of the opening was initiated by tensile cracking at the mid-section of the immediate roof layer. The loading frame test results have been back-analysed using a Cosserat Continuum Finite Element code. In the finite element formulation, the layers have been assumed to be elastic with equal thickness and equal mechanical properties; whereas the inter-layer interfaces (joints) have been assumed to be elastic perfectly-plastic. It is observed that the present Cosserat continuum model accurately predicts the experimental displacements everywhere, except for the roof region where the prediction is accurate up to a certain load level beyond which the experimental displacements increase more rapidly than those predicted by the numerical model. It is shown that the load, at which the measured displacements start to deviate noticeably from those obtained from the numerical prediction corresponds to the critical load that may initiate cracks in the roof layer.