A practical tool for the stability estimation of underground quarries in North France

The presence of underground quarries in North France in close proximity to urbanized areas, imposes serious problems in terms of security of both people and constructions at one hand, and induces a strong constraint against planning and urban development on the other hand. The purpose of this paper is to provide a practical tool for the preliminary estimation of the stability of underground quarries.,In this paper, a numerical stability study of quarries, excavated in chalk of North France with or without joints, by the method of rooms and pillars, is presented. This integrates the data provided from site: mechanical properties of the chalk and geometric characteristics of the quarries (width of the pillar W, height of the pillar H and span between pillars L), as well as the orientation of the joints (α). Numerical parametric analysis is conducted using FLAC 3D. Factors of safety are computed from the numerical models. Then, a second-order regression technique is applied on these numerically obtained factors, to correlate new formulae.,As a result, user-friendly formulae for the calculation of factors of safety Fs (ex) are extrapolated. Besides, abacuses to determine the minimum permissible effective width of safe pillars are proposed.,By this, it becomes possible, knowing only few parameters about geometry and properties, to give a fast estimation of the stability state of any quarry in the region.