The demand for ornamental stones increases day by day due to their use in modern architecture. This increase has led to the intensive exploitation of the existing marble quarries. The immediate result is the diminution or even the exhaustion of the known surface deposits. Additionally environmental reasons enforce the underground marble exploitation.

In spite of this fact the scientific knowledge of underground marble quarries is very limited. Actually underground marble quarries don't have much in common with other forms of underground mines (the dimension of openings, the method of excavation, the form of the excavated material, the support method etc). The exploitation is empirical and based more on experience than on scientific knowledge. This uncertainty discourages other exploiters to do the big step and go underground.

The project - Partners and goals

The E.U. being aware of the problem, has approved a research project (duration 36 months) with the participation of several parts (educational foundations and production units) for the development of an integrated computer aided design and planning methodology for underground marble quarries.

The partners who are involved are the following:

1. DIONYSSOMARBLE Co S.A. (coordinator)
2. Cooperativa Condomini Lavoratori dei Beni Sociali di Levigliani s.c.r.l. (CCLL)
3. Lasa Marmo SpA

And the educational foundations:

1. Institut National de l'Environnement Industriel et des Risques (INERIS)
2. Politecnico di Torino, Dipartimento di Georisorce e Territorio (POLITO)
3. Technische Universität Berlin (TU Berlin)
4. Centro Studi per la Fisica delle Rocce e le Geotecnologie (CNR)

The goals of the project are:

1. The optimization of the extraction process of marble quarries for a given fracture system pattern and quality will result that the minimum amount of resource material necessary for safe and reliable operation of the production system would be left in place.

2. A natural extension of the above is the achievement of maximum productivity-and thus economic returns-in an operating quarry, since practice indicates that material recovery and productivity are rarely optimal, because they fail to exploit the full potential of the adopted exploitation technique(s).

3. Optimization of the rock reinforcement and support systems will allow the reduction of the exploitation cost, since reinforcement failures and unnecessary supplementary or reinstallation of roof reinforcement will be minimized.

4. Availability of decision support techniques based on integrated expert knowledge of geomechanical rock behaviour, deposit geometry, and rock quality distribution will support the marble mining companies in designing underground openings optimized in terms of safety, productivity and economy.

5. Prediction of the recovery (size, quality and quantity) of the excavated blocks and the optimization of it with the use of modern computer based techniques.

6. Dissemination and exploitation of the outcome of the project.
Description of the methodology of underground marble mining

The method that is used in underground marble quarrying is room and pillar. The first step is to excavate a gallery into the deposit, which later will be expanded to create a room. A part of the deposit will be left in place as a pillar in order to support the roof. A pattern of several rooms and pillars will be formed during the progress of the excavation. The dimensions of them are depending on the experience of the exploiter, since there is no scientific methodology in underground marble quarries.

After the completion of the first floor the exploitation continues on the second floor, following the pattern of rooms and pillars of the first floor. This procedure will be repeated as the excavation goes deeper.

The support method that is followed is bolting the roof and the pillars in order to reinforce them.

Description of the research methodology

The lack of scientific knowledge in underground marble quarrying led the E.U. to initiate a research project with the participation of several industrial and academic partners. The whole project is divided in two periods. In the first period (duration 24 months) a room was excavated in each site, around a square pillar (15 x 15 m). During this phase all the appropriate instrumentation (multiple borehole extension meters, stress meters, convergence stations) was installed to monitor the rock mass state of stress and deformability. Furthermore thorough investigation of the rock mass geomechanical properties through field surveys and laboratory tests took place. Based on the data collected, a 3D rock block model as well as appropriate numerical models of the roof-pillar-floor system were developed.

On the second phase the knowledge acquired during phase A will be applied on the exploitation of the experimental sites. Modern computer based decision support system will be used to advise for the selection of the most cost effective and safe quarry layout. In this way it is possible to evaluate the effectiveness of the system. Further exploitation of the test sites will provide the system with all the necessary information to enrich the database, so as the decisions will be more accurate.

Industrial partners (Dionyssomarble, Lasamarmo and CCLL)

The industrial partners have to carry out the excavation of the afore mentioned room around a pillar. During the progress of the excavation they are obligated to install all the appropriate instrumentation and to take frequent measurements. Meanwhile more instruments are installed with the progress of the excavation, according to the specifications of the project. All the data are send to the academic partners in order to elaborate them. Finally the room has to be expanded, so that any alterations in the stress condition and deformability of the roof can be studied and the academic partners can reach to safe conclusions.

Academic partners

The academic partners carrying out the mechanical characterization of the rock materials (over 850 specimens have been tested so far). They also designed the systems of geomechanical monitoring to be installed in the experimental room and pillar and the verification of the performance of these systems (CNR).
Another aspect they work on is the development of a software (RESOBLOCK), which reproduces the discontinuities of the rock mass in a 3D model. The input of the software is a 2D depiction of the discontinuities (with orientation and inclination of the fractures), as well as, the characterazation of them, according to the extension of them, the filling material, the roughness and the opening. Thus the software can display a 3D model of the expected blocks. RESOBLOCK in the first phase of the project was fed with data and produced a model. This theoritical model will be verified and calibrated with data collected during the second phase of the project, with actual data (INERIS).

Subsequently the outcome of the tasks performed by CNR and INERIS will be used by POLITO in order to develop a numerical model for each quarry. POLITO's methodology is based on Distinct Element Model (DEM). According to this model the whole marble deposit consists of rigid and deformable blocks and dispalcements are then due to joint movements.
The theory which supports that the blocks, that constitute the pillar are rigid allows a reliable assessment of the global stability conditions with a shorter computational time than the deformable one. On the other hand the deformable blocks theory, allows a more detailed computation path of stress, strain and displacement. With the development of this model it will be possible to calculate the stresses which will be grow with a wide opening excavation, as well as, the expected displacement of the roof and the walls of the room. Finally all the knowledge provided from the afore mentioned partners has to be presented to the interested parts. The aim of TUBERLIN is to develop a decision support system (DSS) for cost, safety and quality effective mine designs applicable in underground marble mining. The DSS addresses itself to companies that plan to start the underground mining of marble and to companies that already operate marble mines. The first group will be supported in its planning steps for the mine layout, while the second will receive assistance in optimizing and modifying an existing mine design. The decision support system software in the early stages will produce an optimized quarry layout. This layout will be calibrated according to actual data while the DSS database is being enriched with additional information in order to become more reliable and accurate.

Progress state

The project now is on the 24th month since it has been commenced. In November 2000 the 2nd annual meeting took place in Berlin. The main issues discussed were of technical matters. It was also announced the completion of phase A and advance to phase B. Besides these, all the partners manifested their common will to disseminate and exploit the outcome of the project.