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STABILITY AND REINFORCEMENT OF MINE WORKING. DEVELOPMENT OF DIMENSIONING METHODS BASED ON GEOSTATIC STUDIES OF FRACTURE AND ON THE KEY BLOCK METHOD. APPLICATIONS TO CABLE BOLTING.

Objective

THE AIM OF THE PROJECT IS TO FORMULATE A METHODOLOGY ENABLING THE FISSURATION OF ROCK TO BE OBJECTIVELY OBSERVED WHEN ASSESSING THE STABILITY OF OPEN-CAST AND UNDERGROUND MINES AND DESIGNING THEIR SUPPORT.
THE RESEARCH SHOULD AID THE DEVELOPMENT OF SUPPORT SYSTEMS SUITED TO LARGE-SCALE UNDERGROUND WORKINGS, PARTICULARLY ROOF BOLTING BY CABLE.
Methods of evaluating mine stability have been investigated both in underground and in open situations. Methods of evaluating mine dimensions have also been assessed with a view to better safety being achieved during exploitation.

The objective of the work was to apply structural analysis, geological mapping, geostatistics and the key block method to the study of problems of stability and the reinforcement of rock masses in mine workings. Improvement of the methods of assessing the stability of workings in rock and the dimensioning of the support provides a realistic decription and geometrical outline of the fracturing of rock masses. A computation code combining geostatical study of the fracturing with stability analysis of the blocks it delimits has been developed based on the theory of key blocks. The model presented enables any structuring, in the geostatistical sense of the word, of the natural fracturing of rock masses to be taken into account, and the stability of the rocks, bounded by fractures of finite dimensions and intersected by underground workings or open pits, to be identified and assessed. it is therefore easier to define and dimension the means of support to be used, such as cable bolting, to ensure the safety of the working. The results of the modelling developed on this project indicate considerable scope for rationalizing support requirements (bolts/cables) in blocky rock. The result of this work may be a generally acceptable set of probabilistic equations for block
size and frequency and for support requirements. The development and proving in different workings of a device for the point measurement of the forces working on support cables undoubtedly contribute to an improved understanding of the interactions between the rock mass and the support.
IT IS TO CONSIST OF THE FOLLOWING PHASES :

I. DESCRIPTION AND MODELLING OF ROCK FISSURATION :
STRUCTURAL ANALYSIS OF OUTCROPS, BOREHOLES OR ROADWAYS; GEOSTATISTICAL STUDY AND MODELLING.
II. STABILITY ANALYSIS:
APPLICATION OF THE KEY BLOCK METHOD : DEVELOPMENT OF PROBABILISTIC STABILITY CALCULATION MODELS.
III. VALIDATION OF MODELS ON ACTUAL SITES IN FRANCE AND ENGLAND.
IV. CABLE BOLTING. VALIDATION OF FORCE SENSORS MEASURING CABLE TENSION. EQUIPMENT AND MONITORING OF AN EXPERIMENTAL MINE IN SPAIN.

THE OBJECTIVE OBSERVATION OF ROCK FISSURATION AND GEOSTATISTICAL MODELLING SHOULD RESULT IN BETTER DESIGN METHODS FOR MINES AND THEIR SUPPORTS.
BY IMPROVING THE ELEMENTS REQUIRED FOR CORRECT DESIGN, THIS METHOD SHOULD ENABLE CABLE BOLTING TO BE IMPROVED AND LARGE-SCALE UNDERGROUND WORKINGS TO BE EXCAVATED, POSSIBLY LEADING TO APPRECIATE GAINS IN MINE PRODUCTIVITY.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Bureau de Recherches Géologiques et Minières (BRGM)
Address
39-43 Quai André Citroën
75739 Paris
France

Participants (1)

Camborne School of Mines
United Kingdom
Address
Pool
TR15 3SE Redruth