To reactivate the top slicing method but replacing the wooden sets with concrete chocks which can slide on the walls.
The old mining method of top slicing under caving was frequently used in Europe 50 years ago and provided good economical results in nonmechanized mines, but the mechanization of the method has been nearly impossible, until now. The old method has been updated by mechanizing the installation and removal of roof support, for subvertical veins with natural caving.
Prototypes of hydraulic props have been designed and manufactured, in order to solve the problem, as well as a manipulator dedicated to installation and removal of the props. The scope of the mechanized method covers veins whose thickness varies from 3 to 4 metres and inclination from 60 to 90 degrees.
The economical evaluation of the method in the Bourneix mine showed very promising results in terms of payback (around 3 years, where the new method replaces the old bolted and grill fitted one).
The mechanical stresses created with the top slicing under caving method were less important than with cut and fill methods. This has been directly measured in the existing wooden cut and fill stopes, as well as confirmed by finite element calculations. Such a lower stress condition directly reduces the mining costs.
The research comprises the following phases.
The first phase is the studies and preliminary trials which will involve the following:
further development of the sliding chocks developed by Coreal;
study of the viability of the top slicing project with sliding chocks;
design, study and development of different types of sliding chocks or slabs to support the open slices in the subvertical lodes of the metal mines participating in this research;
development of a prototype sliding chock and the ancillary equipment for the 2 contracting mines;
design of the adaptations to the sliding chocks to enable them to support a flexible floor accompanying the descent of the chocks or a continuous metal grating positioned in step with ore extraction to contain the caved material;
preliminary trials in open workings and comparative studies of the capital cost of metal and concrete chocks;
development of the simulation software;
and study of the safety and feasibility of the method. .SP 0 The CGES will participate in the studies for the choice of site. In particular, the fissuration studies carried out in the walls will establish the caving characteristics of the overlying wall. To this end, CGES will develop software characterising the cave in properties of the overlying wall which will be communicated to the other research participants.
The second phase is the in situ trials in 2 mines.The CGES will carry out the following studies during the in situ trials (at the Bourneix mine):
measurement of the mechanical properties of the walls and the lode;
measurement of the thrust of the chocks on the walls using Gloetz jacks or similar;
measurement of the stresses on the bearing elements of the sliding chocks by means of gauges buried in the concrete;
measurement of the expansion of the material in the overlying wall in the slices being worked supplemented by endoscopic readings, the purpose being to establish the geometry of the caved areas and their chronology;
structural study of sliding chocks with a view to reducing as far as possible their weight and bulk with account taken of the stresses measured in situ;
and measurement of surface collapse.
In one of its mines, the Societa Italiana Miniere undertakes to carry out a trial with top slicing using sliding chocks over a minimum working length of 30 m and a minimum sample of 10 slices.
The final phase is the drafting of the final report which will be submitted to all the participants for approval at the end of the trials in France and Italy (Sardinia). This report will concern not only technical questions, but also economic comparisons which can be made on the basis of these trials between the cut and fill and top slicing methods on the one hand and between top slicing under concreted fill and top slicing on the other.
Funding SchemeCSC - Cost-sharing contracts
09016 Iglesias Cagliari
87500 Le Chalard