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CATACLASTIC PLASTO-ELASTIC EQUILIBRIA IN BRITTLE ROCK UNDER TRIAXIAL DIFFERENTIAL LOADING CONDITIONS

Objective

THE MAIN TOPIC OF THIS RESEARCH IS THE STUDY OF FRACTURING BEHAVIOUR OF ROCK IN RELATION WITH THE STABILITY OF MINE OPENINGS IN ORDER TO DEVELOP MATERIAL PROPERTIES INCLUDING THOSE CONTROLLING THE STRAIN SOFTENING BEHAVIOUR OF ROCK TYPES.
The main topic of research was the study of the fracturing behaviour of rock and rock masses in relation to the stability of mine openings. Material properties were investigated including the strain softening and volumetric behaviour of rock. Understanding of the deformation mechanisms occurring is important when translating laboratory data (rock properties) into in situ data (rock mass properties). By introducing the developed stress strain relations into finite element or finite difference calculations the forecasting value of numerical simulations concerning the rock around mine openings can be improved.

Conventional test series (uniaxial and conventional triaxial) were out to provide reference data. However, of greater importance were the sophisticated true triaxial test series that were carried out to study complex material behaviour including postfailure behaviour. Cubes with edges of 105 mm and 115 mm of different rocks were tested and properties and failure mechanisms were studied under several true triaxial loading conditions. The samples were deformed far into the plastic range.

The results of the tests were adapted to rock mass behaviour and introduced into numerical simulation calculations in order to verify the applicability of the complicated material behaviour observed in the tests. Also calculations were made concerning the underground situations at the coal mine of Houilleres du Bassin du Centre Midi (HBCM). Here the rock mass properties have to be based on a limited number of tests (the material is not very suitable for testing or is poorly accessible) and on investigation of the deformation mechanisms. The results of these calculations are compared with measurements and observations carried out in this mine.

The main topic of this research was the study of fracturing behaviour of rock and rock masses in relation to the stability of mine openings. Material properties were investigated including the strain softening and volumetric behaviour of rock. Understanding of the occuring deformation mechanisms is important when translating laboratory data (rock properties) into in situ data (rock mass properties). By introducing the thus developed stress strain relations into finite element or finite difference calculations the forecasting value of numerical simulations concerning the rock around mine openings can be improved.
Sophisticated true triaxial test series were carried out to study complex material behaviour including post failure behaviour. Cubes with edges of 105 and 115 mm of different rocks were tested and properties and failure mechanisms were studied under several true triaxial loading conditions. The samples were deformed far into the plastic range. The results of the tests were, adapted to rock mass behaviour in order to verify the applicability of the complicated material behaviour observed in the tests.
The main part of the work was carried out in the laboratory for rock mechanics in Delft, using its testing facilities, including the true triaxial compression machine. In situ measurements and observations regarding rock-mechanical conditions of mine openings and the surrounding rock masses to which the numerical simulations were applied were carried out in an actual mine.
THE FORECASTING VALUE OF THE ULTIMATE STRESS-STRAIN BEHAVIOUR OF ROCK AROUND OPENINGS CAN BE PREDICTED MORE ACCURATELY THAN PRESENTLY POSSIBLE. THIS WILL CONTRIBUTE TO MORE RATIONAL MINE PLANNING WITH RESPECT TO ROCK MECHANICS RESULTING IN FINANCIAL ECONOMIC BENEFITS TO THE MINE EXPLOITATION.
EXPERIMENTS WILL BE CARRIED OUT WITH A UNIQUE TRUE TRIAXIAL COMPRESSIVE MACHINE, PROVIDED WITH A VERY SOPHISTICATED MEASURING SYSTEM.
THE GENERAL OUTLINE OF THE PROPOSED RESEARCH PROGRAM IS AS FOLLOWS : CUBES WITH EDGES OF 120 MM WILL BE TESTED, AND MATERIAL PROPERTIES AND FAILURE MECHANISMS WILL BE STUDIED UNDER MULTI AXIAL LOADING CONDITIONS. RESULTS OF THE TESTS WILL BE INTRODUCED INTO FEM-CALCULATIONS IN ORDER TO VERIFY THE APPLICABILITY OF THE OBTAINED DATA. EVIDENTLY THESE CALCULATIONS ARE TO BE MADE AT SEVERAL PROJECT STAGES.

THIS STUDY WILL PROVIDE AN EVALUATION AS TO THE APPLICABILITY OF THE RESULTS OF THE RESEARCH FOR APPLIED USE OF CALCULATIONS AS THE FORECASTING VALUE OF THESE CALCULATIONS IS DEFINITIVELY ENHANCED.

IT IS EXPECTED THAT THE RESULTS WILL MAKE IT POSSIBLE, WITH RESPECT TO ROCK MECHANISMS, TO IMPROVE MINE PROCEDURES, WITH INHERENT FINANCIAL-ECONOMIC BENEFITS TO EXPLORATION COSTS. MINE SAFETY ASPECTS CAN BE ALSO IMPROVED.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

TECHNISCHE UNIVERSITEIT DELFT
Address
Julianalaan 134
2628 BL Delft
Netherlands

Participants (1)

HOUILLERES DU BASSIN DU CENTRE DU MIDI
France
Address

Montceau-les-mines