Modelling of Short-Term Interactions Between Concrete Support and the Excavated Damage Zone Around Galleries Drilled in Callovo–Oxfordian Claystone

peer reviewedProduction of energy from nuclear power plants generates high-level radioactive nuclear waste, harmful during dozens of thousand years. Deep geological disposal of nuclear waste represents the most reliable solutions for its safe isolation. Confinement of radioactive wastes relies on the multi-barrier concept in which isolation is provided by a series of engineered (canister, backfill) and natural (host rock) barriers. Few underground research laboratories have been built all over the world to test and validate storage solutions. The underground drilling process of disposal drifts may generate cracks, fractures/strain localisation in shear bands within the rock surrounding the gallery especially in argillaceous rocks. These degradations affect the hydro-mechanical properties of the material, such as permeability, e.g. creating a preferential flow path for radionuclide migration. Hydraulic conductivity increase within this zone must remain limited to preserve the natural barrier. In addition galleries are currently reinforced by different types of concrete supports such as shotcrete and/or prefab elements. Their purpose is twofold: avoiding partial collapse of the tunnel during drilling operations and limiting convergence of the surrounding rock. Properties of both concrete and rock mass are time dependent, due to shotcrete hydration and hydromechanical couplings within the host rock. By the use of a hydro-mechanical coupled Finite Element Code with a Second Gradient regularization, this paper aims at investigating and predicting support and rock interactions (convergence, stress field). The effect of shotcrete hydration evolution, spraying time and use of compressible wedges is studied in order to determine their relative influence

Analysis of Fracture Mechanics Tests on Opalinus Clay

Many studies have recently been conducted to evaluate various mechanical characteristics of the Opalinus Clay (OPA) formation in view of its potential use as the hosting rock for the Swiss nuclear waste repositories. Its sedimentary bedding makes OPA a transversely isotropic rock and its directional mechanical properties need to be measured. This paper reports on an experimental and computational approach that was adopted to define the parallel-to-bedding fracture mechanics (FM) parameters of OPA in Mode-I. OPA cores from Mont Terri Underground Research Laboratory (URL) were submitted to laboratory tests on notched semi-circular specimens under three-point bending (SCB). In these tests, crack propagation is forced along the notch direction. However, the 45° bedding inclination of the specimen axis frequently deviated the crack from the expected direction. An analysis of the SCB tests was performed by means of non-linear FM techniques and the pertinent Mode-I parameters along the bedding were estimate

Télésurveillance des excavations souterraines par des mesures de déformation (CIUS)

The Niobec mine is located in St-Honore 15 km north-east of Chicoutimi (Quebec, Canada) and produces Niobium at a rate of 815,000 metric tones annually. Exploitation is done using the Long Hole method with sill and crown pillars at the levels 300-600 (90-180m) and 700-1000 (200-300m). For economic reasons, no backfill has been used at this mine. As a result, stopes with a minimum 100 meters in height have been left open since excavation. Mining activity take places in a carbonatite pluton located in the Pre-Cambrian Shield. The carbonatite and host rocks are capped by flat lying limestone. Six CIUS (Cylindre Instrumente de l'Universite de Sherbrooke) have been installed at this mine. The CIUS is a cylindrical concrete inclusion, instrumented with vibrating wires, installed in a borehole and used to follow the variations of stress and deformation in the host medium (rock mass). The objectives of instrumentation at this mine by the CIUS are to monitor the variations of stress and deformation. The thesis presents the development and application of a probabilistic model for prevention and prediction of in-situ rock mass failure. The programming procedure of a rock failure warning system (Alarm System) using the CIUS' data has also been presented. The algorithm of this model operates on the basis of the detection of the anomalies on the deformation rates, recorded by the CIUS. The warning system contains the CIUS and an acquisition system, developed at the Universite de Sherbrooke (CAIUS), in which the algorithm of the preventive model can be implanted. It has been shown that this unit can offer the continuous remote monitoring of underground structures, regardless where they are located

Télésurveillance des excavations souterraines par des mesures de déformation (CIUS)

The Niobec mine is located in St-Honore 15 km north-east of Chicoutimi (Quebec, Canada) and produces Niobium at a rate of 815,000 metric tones annually. Exploitation is done using the Long Hole method with sill and crown pillars at the levels 300-600 (90-180m) and 700-1000 (200-300m). For economic reasons, no backfill has been used at this mine. As a result, stopes with a minimum 100 meters in height have been left open since excavation. Mining activity take places in a carbonatite pluton located in the Pre-Cambrian Shield. The carbonatite and host rocks are capped by flat lying limestone. Six CIUS (Cylindre Instrumente de l'Universite de Sherbrooke) have been installed at this mine. The CIUS is a cylindrical concrete inclusion, instrumented with vibrating wires, installed in a borehole and used to follow the variations of stress and deformation in the host medium (rock mass). The objectives of instrumentation at this mine by the CIUS are to monitor the variations of stress and deformation. The thesis presents the development and application of a probabilistic model for prevention and prediction of in-situ rock mass failure. The programming procedure of a rock failure warning system (Alarm System) using the CIUS' data has also been presented. The algorithm of this model operates on the basis of the detection of the anomalies on the deformation rates, recorded by the CIUS. The warning system contains the CIUS and an acquisition system, developed at the Universite de Sherbrooke (CAIUS), in which the algorithm of the preventive model can be implanted. It has been shown that this unit can offer the continuous remote monitoring of underground structures, regardless where they are located