1,721,023 research outputs found
Re-evaluation of selected hydro-mechanical processes in the near field of a potential nuclear waste repository in the Zuercher Weinland
No full textRecharge areas and geochemical evolution of groundwater in an alluvial aquifer system in the Sultanate of Oman
Full text linkA regional hydrogeochemical model was developed to evaluate the geochemical evolution of different groundwaters in an alluvial aquifer system in the Interior of Oman. In combination with environmental isotopes the model is able to extract qualitative and quantitative information about recharge, groundwater flow paths and hydraulic connections between different aquifers. The main source of water to the alluvial aquifer along the flow paths of Wadi Abyadh and Wadi M’uaydin in the piedmont is groundwater from the high-altitude areas of the Jabal Akhdar and local infiltration along the wadi channels. In contrast, the piedmont alluvial aquifer along Wadi Halfayn is primarily replenished by lateral recharge from the ophiolite foothills to the east besides smaller contributions from the Jabal Akhdar and local infiltration. Further down gradient in the Southern Alluvial Plain aquifer a significant source of recharge is direct infiltration of rain and surface runoff, originating from a moisture source that approaches Oman from the south. The model shows that the main geochemical evolution of the alluvial groundwaters occurs along the flow path from the piedmont to the Southern Alluvial Plain, where dedolomitization is responsible for the observed changes in the chemical and carbon isotope composition in these waters
Characterizing excavation-induced perturbations around a short tunnel in an overconsolidated clay shale
No full textThe Opalinus Clay is under investigation for deep geological disposal of nuclear waste in Switzerland. Past investigations indicate that the Excavation Damaged/Disturbed Zone is comprised of macroscopic fracturing. Recent excavation of the EZ-B niche at the Rock Laboratory revealed only a few induced macroscopic fractures from drillcore mapping and televiewer imaging. However, borehole seismic profiling showed marked velocity and amplitude decreases within the first 50 cm. Due to the limited induced macroscopic fracturing identified, the zone of excavation-induced perturbation was characterized through the integration of borehole data to reveal a non-uniform zone around the niche. ©2008, ARMA, American Rock Mechanics Association
Characterizing excavation-induced perturbations around a short tunnel in an overconsolidated clay shale
No full textThe Opalinus Clay is under investigation for deep geological disposal of nuclear waste in Switzerland. Past investigations indicate that the Excavation Damaged/Disturbed Zone is comprised of macroscopic fracturing. Recent excavation of the EZ-B niche at the Rock Laboratory revealed only a few induced macroscopic fractures from drillcore mapping and televiewer imaging. However, borehole seismic profiling showed marked velocity and amplitude decreases within the first 50 cm. Due to the limited induced macroscopic fracturing identified, the zone of excavation-induced perturbation was characterized through the integration of borehole data to reveal a non-uniform zone around the nich
Characterisation of excavation-induced damage around a short test tunnel in the Opalinus Clay
No full textCharacterisation of excavation-induced damage around a short test tunnel in the Opalinus Clay
No full textIn Switzerland, the Opalinus Clay is under consideration as a potential host rock for deep geological storage of nuclear waste. The Swiss concept involves high-level waste containers emplaced in small-diameter drifts of roughly three metres. At the Mont Terri Underground Rock Laboratory, a short mine-by experiment (EZ-B) was executed in 2005 with the objective of characterising the excavation-induced damage through an interpretation of integrated field data. The damage zone was found to consist of two parts. Fracture mapping from drillcores and televiewer images revealed a thin inner zone of macroscopic fracturing (20 cm) and devoid of borehole instabilities as well as coinciding with the lowest P-wave characteristics (normalised amplitudes and velocities). The outer zone (50 to 80 cm) was defined by increasing P-wave
characteristics and evidence of borehole instabilities. Supplementing the data interpretation, a simplified numerical elastic stress analysis indicated that the rock mass in the sidewalls and upper western haunch are the most susceptible to spalling.
In these regions, stress levels only just reach a spalling limit around 0.05 in the inner fractured zone, suggesting that the zone of macro-fracturing around the niche is not significant. It is postulated that the physical manifestation of the relatively weak bedding plane strength is dominated by bedding-perpendicular displacement as opposed to bedding-parallel shea
Analysis of Fracture Mechanics Tests on Opalinus Clay
Full text linkMany 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
- …
