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The mechanization of marble cutting operations thrusts the enlargement of quarry exploitations. This trend makes necessary the geomechanical control and computations of the static condition both at the exploitation workplaces and of the residual rock structures (HOEK & BRAY, 1981, HOEK & BROWN, 1982, BRADY & BROWN, 1985, BIENIAWSKI, 1989). Planning of the investigations is driven by the specific geostructural and mechanical rock mass characteristics of the quarry sites in respect to the natural morphology and the excavation geometries (CRAVERO et al., 2003). For instance in open pit quarrying, the monitoring of the structurally controlled deformation of high excavated rock faces is relevant for safety and planning of further quarry developments. The paper reports an experience of monitoring and computations at an open pit quarry. The quarry site belongs to the Alpi Apuane marble basin (Carrara marble), where past exploitation operations left in place a parallelepiped marble spur ?90m high, horizontal section ?30mx20m and hosting old drifts (Fig. 1). This residual rock structure is intersected by different rock joints and a sub-vertical large fault located on the back side of the spur. Evident joint traces appear on the excavation and drift surfaces, and a monitoring plan was defined which allows to detect the influence of rock fractures on the deformation behaviour of the marble spur. Groups of different measuring devices (1D or 3D crack gages, MPBX extensometers, load cells and piezometer) were arranged on the surface and in the old drifts (Fig. 2) while a wireless transmission system conveys the measured data to the quarry technical office (DUNNICLIFF, 1993). Hydraulic fracturing was furthermore applied in two vertical boreholes located on the two opposite sides of the big fault to detect the stress condition (HAIMSON, 1993, AMADEI & STEPHANSSON, 1997). Computations were made to estimate the influence of the rock mass structure and of the environmental condition on the static behaviour of the rock spur. The Block Theory (BT) technique (GOODMAN & SHI, 1985). was applied to detect potentially unstable rock blocks defined by rock joint intersections in the marble spur (Fig. 3). FEM modelling, made by using the commercial software Phase, allowed to clarify the possible role played by the fault and by different stress or water load conditions on the deformation mechanism shown by the spur (Fig. 4). The experimental control along with the analysis of unwanted deformation and rock block instabilities was motivated not only by the need of controlling the evolution of the displacements, but also suggested setting up remediation countermeasures against a possible unstable trend of the marble spur.

The proposed paper is aimed at analysing a rock slope failure that occurred in a sector of an open pit quarry. The failed rock volume was not large, it had a significant impact on the mining operations and the safety of the district road which runs very close to the quarry site. An evaluation of the possible failure mechanisms is given, which was based on a structural description of the rock mass, a mechanical laboratory characterisation of the rock and of rock joints, and on the environmental and exploitation condition. The analysis referred to schemes that could explain the degree of instability of the rock slope. Kinematical analyses, block theory and limit equilibrium were applied and evaluations were also obtained by using DEM models to estimate the static behavior and possible effects induced by quarry blasts of the rock slope.

The paper reports a geomechanical monitoring and measurements experience at an open pit quarry. The quarry site belongs to an Alpi Apuane white marble basin (Carrara marble), where intensive quarry exploitations (both open pit and underground) have been developed. The high level of mechanization and new marble cutting technology have favoured an increase in these exploitations making an experimental evaluation of the static condition, both at the exploitation workplaces and of the permanent residual rock structures, necessary. Planning of the ground control was driven by the specific geostructural and mechanical rock mass characteristics of the site in consideration of the particular geometry of the residual rock face. This control activity plays an important role on the safety and planning of further quarry deepening. The potential of rock block instabilities was estimated on the basis of a geostructural rock mass characterization and the block theory. A monitoring program of the structurally controlled deformation of the excavated rock face was set up and it allowed a displacement progression to be detected at some locations on the rock face. Hydraulic fracturing stress measurements were also carried out at different locations and depths on quarry floor of the quarry and they showed a high horizontal stress level at a shallow depth.

Nel lavoro si presenta un esempio di caratterizzazione e controllo geomeccanico in un cantiere per l'estrazione del marmo, ubicato nelle Alpi Apuane. La cava, già sfruttata a giorno, attualmente si sviluppa anche in sotterraneo in condizioni di parietalità. La caratterizzazione della massa rocciosa ha compreso oltre a saggi meccanici di laboratorio sul materiale oggetto di coltivazione la definizione dei principali sistemi di fratture naturali e la valutazione sperimentale dello stato di sollecitazione mediante la tecnica della fatturazione idraulica. La valutazione del regime tensionale agente al contorno degli scavi è stata condotta mediante modellazione numerica 3D, cosi da porre in relazione lo stato di sollecitazione misurato con quello risultante dal calcolo. E' stata inoltre suggerita una stima della possibile influenza delle discontinuità sulla stabilità del cantiere sotterraneo.

La presente relazione raccoglie i risultati delle determinazioni di stato di sollecitazione (relativa) piana e tridimensionale, effettuate con la tecnica del rilascio tensionale mediante sovracarotaggio nei cantieri di coltivazione della cava denominata "Piastriccioni B - n°5", ubicata nel bacino marmifero di Pescina - Boccanaglia, nel Comune di Carrara (MS).

This paper reports the results obtained in a study on an old, presently inactive, landslide which developed in a calcschist bedrock, near an inhabited zone. The sliding phenomenon conforms to the rock mass structure as the sliding surface is shaped by schistosity joints. The geometrical and mechanical characteristics of schistosity joints are evaluated by means of an in situ survey and laboratory testing. The experimental results and static analysis (limit equilibrium method and stress analysis) allow one to infer the shear strength parameters that are representative of in situ joints. This characterisation is then used to estimate thc static condition of a ground mass that is larger than the landslide itself and which extends uphill to the inhabited zone.

The underground exploitation of ornamental stone, particularly when exploited with mechanized techniques (diamond wire or chain saw) creates big voids in relatively short time. This locally involves the continuous (relatively quick) intensification of the stress state of the exploited rock mass particularly near the cutted free surfaces (slopes, walls, roofs, ...). As a result the stress-strain state of the abandoned support elements of the exploited underground chamber (pillars and diaphragms) and therefore their stability conditions vary with the progress of the exploitation. This implies the need of a continuous monitoring. Besides,not less important to the stability assessment of the underground exploitation chamber it is the role of the natural discontinuities. This involves the knowledge of the attitude and of the geomechanical strength characteristics of the joints in comparison to the free surfaces of the exploitation void as well as of the support elements.