Patterns of stress and strain distribution during deep mining at Boulby, N. Yorkshire

The understanding of stress-deformation state transmission within the rock mass above deep mine workings is a key factor to the comprehension of the response of rock masses to changes of stress regime brought about by the mining activity for the safety of surface and subsurface structures. Based on monitoring data from active actual mine workings, this study numerically analyzes factors controlling stress and deformation using the 2D Fast Lagrangian Analysis of Continua (FLAC 2D) code and a strain-softening model to approximate creep behaviour of rock masses. The results show that distribution of stress and deformation at Boulby mine is primarily governed by the lithological heterogeneity of the overlying strata and the geological structure, including its nature within the undermined area. Data from a bespoke roof-to-floor monitoring closuremeter indicate that convergence of openings is a function of local variables, including the site location, geometry and age of the site. Patterns of ground subsidence are compared to the pattern of levelling-based measured ground subsidence. Furthermore, the analysis shows that the strain-softening model reasonably approximates the creep behaviour of the excavations. The results have implications for how we monitor and model subsidence due to mining deep excavations