Geomechanical model of floor heave in long deep underground excavations

Purpose. To develop an adequate geomechanical model of floor heave in long-term underground excavations and to describe the transition from displacement-controlled support loading to load-controlled support loading. Methodology. This involves a step-by-step modelling of the heaving process, taking into account the results obtained at the previous modelling stages and comparing the obtained results with in-situ measurements. The research tool used is the finite element method, implemented in the Phase2 software product from the Canadian company Rocscience. Findings. A multi-stage geomechanical model of floor heave development in long underground openings was developed, taking into account the dilatancy effect under conditions of constrained volumetric deformation. A qualitative pattern of rock mass displacement around the excavation was obtained, showing a 90 % agreement with in situ monitoring data. The process of rock movement at the bottom of a working is approximated by an analytical dependence, on the basis of which it is possible to predict the operational state of capital workings and plan measures for their maintenance. Originality. A digital geomechanical model of the rock mass heaving process around a single, extended working, constructed using the finite element method, is proposed. Unlike the existing models, it simulates the loss of elastic-plastic stability of the rock as a limit state, dividing the lining loading process into two stages: specified deformation and specified load. It has been proven that the process of rock deformation at the base of a permanent working with a cross-sectional area of 15‒20 m2 extends to a depth of 10–15 m. It has been established that maximum vertical displacements occur at the base of the working and decrease exponentially with increasing distance from it. Practical value. The identified regularities of rock mass deformation around horizontal long underground openings under conditions of elastoplastic instability provide a basis for developing methods to control this process in both time and space. This can be achieved through the regulation of mining and maintenance operations during excavation development and service using a dynamic geomechanical model.