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

Abstract

Purpose 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. Design/methodology/approach 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. Findings 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. Originality/value 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.

Numerical Modeling and Back-Analysis Approach on a Monitored Underground Cavern for the Extraction of Marble for Ornamental Uses

“…Through appropriate back-analysis procedures, the measurement findings are processed in order to enhance and increase the reliability of the first estimate of the geomechanical parameters of the rock acquired from the geomechanical classification [11][12][13].…”

“…In the context of excavation and rock engineering, back-analysis refers to a specific process that is developed with numerical analysis techniques for determining the stressstrain states of the rock mass and supporting structures [12,[14][15][16][17]. This process begins with the in situ displacement and stress measurements and allows for the initial estimates of the following parameters to be calibrated using the calculation model:…”

“…Selecting one of the following is necessary to carry out a back-analysis [12]: (a) a representative calculation model that can ascertain the state of stress and strain in the rock mass, taking into account the evolutions of the excavation phases; (b) an error function; and (c) an effective algorithm that minimizes the error (the difference) between the numerical model's calculation results and the observed in situ measurements.…”