Continuous active-source seismic monitoring of brine injections directly in the main fault at Mont Terri, Switzerland

2021 ◽  
Author(s):  
Tanner Shadoan ◽  
Jonathan Ajo-Franklin ◽  
Yves Guglielmi ◽  
Todd Wood ◽  
Michelle Robertson ◽  
...  
Keyword(s):  
Seismic Monitoring ◽  
Active Source ◽  
Main Fault ◽  
Mont Terri

Coupled processes in clay during tunnel excavation

2020 ◽  
Author(s):  
Antonio Pio Rinaldi ◽  
Yves Guglielmi ◽  
Alba Zappone ◽  
Florian Soom ◽  
Michelle Robertson ◽  
...  
Keyword(s):  
Rock Mass ◽  
Fiber Optics ◽  
Fault Zone ◽  
Coupled Processes ◽  
Elastic Response ◽  
Elastic Behaviour ◽  
Main Fault ◽  
A Chain ◽  
Mont Terri ◽  
Waste Repositories

<p><span>Tunnel excavations are known to perturb the hosting rock mass at long distances, with changes in the hydrogeological flow affecting, as well as deforming the rock mass, inducing subsidence in a zone above the tunnel. During the extension of the Mont Terri Underground Rock Laboratory, we had the unique opportunity to monitor the final part of the excavation of Gallery18 and the final breaktrough.</span></p><p><span>The joint effort of two experiments (CS-D lead by ETH Zurich and FS-B lead by LBNL) allowed for a detailed characterization of the poro-elastic response of the rock mass and the Mont Terri Main Fault Zone to the excavation. Geophysical, geomechanical, and hydrogeological monitoring include: (1) pressure monitoring in several borehole intervals; (2) deformation at a chain potentiometer and fiber optics grouted in boreholes (normal to bedding and parallel to fault zone), and platform-tilmeters installed at the tunnel floor, as well as detailed 3D displacement at the SIMFIP probe.</span></p><p><span>All monitoring systems detected major perturbations starting from 15 days before the breakthrough and continuing for several days after it. We summarize the observations and will combine numerical modelling and observed trend to conceptualized the pattern of poro-elastic deformation. The results of the analysis could help shedding light on the poro-elastic behaviour of clay, providing interesting hints for the modeling community and helping in planning of future nuclear waste repositories in such material.</span></p>

scholarly journals Monitoring Stress-Induced Seismic Velocity Changes At SAFOD Using Crosswell Continuous Active-Source Seismic Monitoring (CASSM)

2020 ◽  
Author(s):  
Thomas Daley ◽  
Taka'aki Taira ◽  
Fenglin Niu ◽  
Pierpaolo Marchesini ◽  
Todd Wood ◽  
...  
Keyword(s):  
Seismic Velocity ◽  
Seismic Monitoring ◽  
Active Source ◽  
Seismic Velocity Changes ◽  
Velocity Changes

scholarly journals Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

Solid Earth ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 1-24 ◽  
Author(s):  
Ben Laurich ◽  
Janos L. Urai ◽  
Christian Vollmer ◽  
Christophe Nussbaum
Keyword(s):  
Electron Microscopy ◽  
Fault Zone ◽  
Shear Zones ◽  
Deformation Mechanisms ◽  
Opalinus Clay ◽  
Rock Laboratory ◽  
Main Fault ◽  
Clay Formation ◽  
Mont Terri ◽  
Mont Terri Rock Laboratory

Abstract. We studied gouge from an upper-crustal, low-offset reverse fault in slightly overconsolidated claystone in the Mont Terri rock laboratory (Switzerland). The laboratory is designed to evaluate the suitability of the Opalinus Clay formation (OPA) to host a repository for radioactive waste. The gouge occurs in thin bands and lenses in the fault zone; it is darker in color and less fissile than the surrounding rock. It shows a matrix-based, P-foliated microfabric bordered and truncated by micrometer-thin shear zones consisting of aligned clay grains, as shown with broad-ion-beam scanning electron microscopy (BIB-SEM) and optical microscopy. Selected area electron diffraction based on transmission electron microscopy (TEM) shows evidence for randomly oriented nanometer-sized clay particles in the gouge matrix, surrounding larger elongated phyllosilicates with a strict P foliation. For the first time for the OPA, we report the occurrence of amorphous SiO2 grains within the gouge. Gouge has lower SEM-visible porosity and almost no calcite grains compared to the undeformed OPA. We present two hypotheses to explain the origin of gouge in the Main Fault: (i) authigenic generation consisting of fluid-mediated removal of calcite from the deforming OPA during shearing and (ii) clay smear consisting of mechanical smearing of calcite-poor (yet to be identified) source layers into the fault zone. Based on our data we prefer the first or a combination of both, but more work is needed to resolve this. Microstructures indicate a range of deformation mechanisms including solution–precipitation processes and a gouge that is weaker than the OPA because of the lower fraction of hard grains. For gouge, we infer a more rate-dependent frictional rheology than suggested from laboratory experiments on the undeformed OPA.

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