MONITORING OF UNDERGROUND EXCAVATIONS: MEASUREMENT SYSTEM DESIGN BY NUMERICAL MODELLING

Underground exploitation of ornamental stone can lead to the opening of large voids carried out in a relatively short time especially when mechanized excavation is applied /such as diamond wire or chain cutter). This fact induces a rapid variation of the natural state of stress in the rock mass. Natural stresses vary spatially in the rock mass depending on the three surfaces position and orientation. Active state of stress in the supporting elements (pillars and long pillars) and their stability conditions gradually varies with the progression of the excavation. Consequently stability conditions of the voids must be surveyed by the measurements of the stresses and deformations induced in the rock mass around excavations. Rock discontinuities influence underground structures behavior and have to be taken into account. Preliminary studies performed in three ornamental stone quarries for the design of a system of surveying and controlling of the stability conditions during the excavation are described in the paper. Exploitation have been simulated by 3D modeling reproducing the different excavation phases and geometry. Rock mass deformability and strength features have been determined by laboratory test on the intact materials and by detailed in situ surveys of the gee-structural conditions of the rock masses. Stresses, strains and displacements induced by the excavations have been computed by numerical models. On the basis of these results the typologies, place and timing of installation of the measurements devices have been obtained for the three quarries.