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IMPROVED MINE PILLAR DESIGN AND GROUND CONTROL BY USING ROCK MECHANICS FOR BAUXITE MINING

Objective

The development of a laboratory and field scale and the application of modern rock mechanics techniques and principles on rock behaviour, in mine pillar design and roof control in order to establish safer underground mining conditions under increased extraction rate and reduced mine costs in bauxite mining.
The methodology adopted led to the development of a scientific approach to pillar design in discontinuous rock masses. It can be equally well applied to any underground mine where stability is maintained using natural rock supporting elements and structural problems due to the behaviour of the rock mass are encountered. Such a methodology is more reliable than a purely empirical approach to the design of naturally supported mine layouts in discontinuous rock masses. Validation and calibration of the methodology, through comparison to in situ measurements, offers advantages in terms of safety and ore recovery when compared to other approaches.
The work to be carried out comprises 8 stages. These are as follows.

Stage 1 is the identification of the problem. Collection and evaluation of all existing data. Selection of mines and sites in the mines for the project.

Stage 2 is the geomechanical study. It will include collection of all basic engineering data necessary for a detailed geomechanical study of the sites selected. The mechanical properties and quality indices of the intact rock (bauxite and limestone) determined. A detailed discontinuity study of the rock mass will be carried out using the classical field techniques coupled with photoanalysis. The geomechanical data gathered will allow the establishment of the rock mass characterization.

Stage 3 is the detailed geomechanical study of selected pillars and roof sites. Field and photographic techniques will be used to study the characteristics of the discontinuity patterns present and to identify other rock mass parameters. The rock mass modulus of deformation will be calculated based on the CSIR and Q classification systems. Evaluation of early field results derived from exploration boreholes will be used as guides to an early mining planning. Graphical representation of the discontinuity data of the rock masses and joint cluster analysis by means of probabilistic techniques will be performed.

Stage 4 is the laboratory tests which will be conducted on both the intact rock and on selected rock pieces that include discontinuities. Scale effects will be studied up to the size of the maximum pillar used. The criteria of failure will be established.

Stage 5 is the field tests. The appropriate rock mechanics instruments and equipment will be installed in selected underground locations in order to establish the deformability features of the rock mass. Pillar stress variations will be established as mining proceeds away from the pillar by making use of the previous instrument or additional. Field tests will be carried out using seismic geophysical methods or ground penetrating radar. Equipment improvements, modifications and adjustments will be made in order that the results obtained can be of direct use to this study. A 3-dimensional presentation of the discontinuity patterns present in the bauxite pillars will be attempted using tomographic and geostatistic techniques. Special attention will be given to acoustic emission and microseismic activity of the pillars as a warning before failure. A correlation will be attempted of acoustic pulse propagation characteristics in the rock mass to certain geomechanical rock features and factors.

Stage 6 is the evaluation of results. Application of numerical modelling techniques to describe rock behaviour. Comparison of numerical modelling results to experimental field results derived from underground measurements. Appropriate improvements of the model in order that theory and field results correlate with each other. Suggestions for improvement of the exploitation method being applied.

Stage 7 is the application of the derived model to the design of future underground mines. Necessary modifications affected by the general layout of the mine. Planning will be attempted to include simultaneously a sound theoretical background and reliable field methods in such a way as to supplement each other so that finally a realistic and scientifically fully supported underground design in case of room and pillar mining will result.

Stage 8 is the final joint report.

Coordinator

National Technical University of Athens
Address
42,Odos 28 Octovriou
10682 Athens
Greece

Participants (3)

Bauxite Parnasse Mining Company SA
Greece
Address
21A,amerikis
10672 Athens
Imperial College of Science, Technology and Medicine
United Kingdom
Address
Prince Consort Road
SW7 2BP London
Politecnico di Torino
Italy
Address
Corso Duca Degli Abruzzi 24
10129 Torino