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INTERPRETATION AND VALIDATION OF THERMO-MECHANICAL MODELS RELATING TO THE UNDERGROUND THERMO-HYDRO-MECHANICAL EXPERIMENT AT TENELLES, HAUTE-VIENNE.

Objective

AN UNDERGROUND THERMO-HYDRO-MECHANICAL EXPERIMENT HAS ALREADY BEEN CARRIEDOUT IN THE FANAY-AUGERES MINE AT THE TENELLES SITE IN A MODERATELY FRACTURED BODY OF GRANITE.
THE PURPOSE OF YHE EXPERIMENT WAS THE SPACE-TIME SIMULATION OF THE PHENOMENA ASSOCIATED WITH HEAT EMISSION FROM A WASTE STORAGE FACILITY. THE AGREEMENT DEFINED BY THE LAWS OF SIMILARITY BETWEEN AN ACTUAL SITE AND A REDUCED MODEL IS STRICTLY VALID ONLY IF THE HEAT EMISSION, ACTUAL AND SIMULATED, TAKES PLACE IN A CONTINUOUS MEDIUM. THIS ASSUMPTION OF A CONTINUOUS MEDIUM WAS, MOREOVER, ONE OF THE BASES FOR THE PRELIMINARY DESIGN STUDY.
IN REALITY, THE BODY OF ROCK IS AFFECTED BY A THREE-DIMENSIONAL NETWORK OF UNSATURATED DISCONTINUITIES.
THIS STUDY WILL COVER THREE CATEGORIES OF PHYSICAL MECHANISM WHICH ARE NORMALLY CONSIDERED SEPARATELY:
- THERMAL PHENOMENA
- MECHANICAL PHENOMENA
- HYDRAULIC PHENOMENA (BOREHOLE INJECTION TESTS)
THE RESULTS WILL BE INTERPRETED AT TWO LEVELS:
1. DETERMINATION OF THE EXPERIMENTAL VALUES OF THE PHYSICAL PARAMETERS AND INTERPRETATION OF THE RESULTS AS A FUNCTION OF THE CONDITIONS OF THE MEDIUM (CONDITIONS REGARDING LIMITS, MECHANICAL DISCONTINUITIES, ETC)
2. USE OF MATHEMATICAL AND NUMERICAL MODELS WHICH ARE EITHER AVAILABLE OR WILL HAVE TO BE PREPARED.
THE INTERPRETATION WILL FIRST OF ALL BE DONE SEPARATELY. THE FINAL OBJECTIVE WILL BE TO PROPOSE A MODEL COMBINING ALL THOSE MECHANISMS, SHOULD THIS PROVE NECESSARY AND FEASIBLE.

1.1. THERMAL PHENOMENA
THE EXPERIMENTS ALREADY PERFORMED IN GRANITE MEDIA HAVE DEMONSTRATED THAT HEAT TRANSFER OBEYS FOURIER'S LAW AND CAN HENCE BE CORRECTLY REPRESENTED BY A MODEL BASED ON THE ASSUMPTION OF A CONTINUOUS MEDIUM. A SYSTEM OF FRACTURES THROUGH WHICH A CONSIDERABLE FLOW OF WATER COURSES COULD DISTURB THIS BEHAVIOUR; THE PROBLEM WILL BE STUDIED.

1.2. MECHANICAL PHENOMENA
THE INTERPRETATION OF THE DISPLACEMENT OR DEFORMATION MEASUREMENTS WILL REVEAL THE DISTURBANCES BROUGHT ABOUT BY THE DISCONTINUITIES IN A REFERENCE BEHAVIOUR WHICH WILL BE THAT OF A CONTINUOUS MEDIUM OBEYING HOOKE'S LAW. THE THERMOMECHANICAL CHARACTERISTICS OF THE ROCK MATRIX HAVE HENCE BEEN CAREFULLY MEASURED.
BY USING A MODEL, NUMERICAL SIMULATIONS WILL BE CARRIED OUT WHICH ARE AS FAITHFUL AS POSSIBLE FROM THE STANDPOINT OR BOTH TEST-SITE GEOMETRY AND THE RECORDED HEAT EMISSION.

1.3. HYDRAULIC PHENOMENA
THE DISTURBANCE CAUSED BY THE EFFECT OF HEAT TAKES THE FORM, WHERE THE FRACTURES ARE CONCERNED, OF A VARIATION OF THICKNESS CAPABLE OF GIVING RISE TO A VARIATION IN THE HYDRAULIC PROPERTIES OF THE FRACTURES.
MEASUREMENTS OF THESE CHARACTERISTICS WERE CARRIED OUT WITH DIFFERENT METHODS (INJECTIONS, BOREHOLE LEAKTIGHTNESS MEASUREMENTS) BEFORE, DURING AND AFTER THE HEATING AND COOLING PHASES.
THE INTERPRETATION WILL HENCE CONCERN THE HYDRAULIC BEHAVIOUR OF A NUMBER OF IDENTIFIED FRACTURES.

2. VALIDATION OF THE CALCULATION TOOLS (MODELS)
THIS WILL INVOLVE COMPARING THE EXPERIMENTAL RESULTS WITH THE THEORETICAL FORECASTS DESCRIBED ABOVE.
THE DIVERGENCE BETWEEN THE RESULTS OBTAINED WITH THE MODELS AND THE EXPERIMENTAL RESULTS WILL BE IDENTIFIED. THEY WILL BE COMPARED WITH THE GEOLOGICAL DISCONTINUITIES OF THE NATURAL MEDIUM IN THE EXPERIMENT (PRINCIPAL FRACTURES, DIVERGENCES AS REGARDS DIRECTION AND DENSITY OF THE SETS OF CRACKS, ETC).
THE LAST STAGE WILL BE AN ATTEMPT TO REPRESENT THREE-DIMENSIONALLY THE MAJOR FRACTURES AFFECTING THE BODY OF ROCK UNDER STUDY, WHICH WILL BE DIVIDED BY PLANE JOINTS; AN ATTEMPT WILL BE MADE TO MODEL THE MECHANICAL BEHAVIOUR OF THOSE JOINTS: COHESION, ANGLE OF FRICTION.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Commissariat à l'Energie Atomique (CEA)
Address
Centre D'études De Fontenay-aux-roses
92265 Fontenay-aux-roses
France

Participants (1)

BRGM
Address

Emp