[en] The Tournai's region is characterised by famous outcrops of carboniferous limestone which is mined out for cement and raw material production. The four main quarries found in the Region, i.e. Gaurain-Ramecroix, Milieu, Antoing and Lemay, are owned by the three main cement producers in Belgium: Italcementi, Holcim and CBR. The overall production of limestone is about 20 million tons per year, giving big pits with depths up to about 150m. With the growth of the pits, the quarries are approaching each other leading to the problem of managing the reserves contained in the separating walls and their mechanical stability.
The limestone deposit is composed of different seams having varying thickness, chemical composition and even mechanical properties. The deposit has an overall horizontal dip and is intersected by two main sets of discontinuities with a spacing of about 10m or less. It is also crossed by a set of east to west faults but the quarries are implanted in the in between areas, so to not be crossed by these faults. The layers and specially the shallow ones are characterised by a typical karstic weathering giving open or filled cavities.
This paper presents the global work carried out in order to study the stability of the Lemay quarry. We first describe and measure the orientation and spacing of discontinuities and tried to relate to the development of weathering. Some rock samples have then been retrieved and laboratory tests performed to determine the mechanical behaviour in atmospheric and under confining conditions. We then qualified the rock mass using mechanical and structural properties.
To work as realistically as possible, we coupled a mining planning analysis using a professional mining software with a mechanical approach. We developed a Matlab program to retrieve a three dimension model from the mining tool to create a mesh for a finite element computation. We used continuum models but with adjusted mechanical properties to take into account the presence of discontinuities. Another Matlab program has also been developed to assess the probability of rock slope failure using the strike and dip of discontinuities versus the face orientation from a point to another in the quarry
