scholarly journals Large-scale testing of a sandwich shaft-sealing system at the Mont Terri rock laboratory

2021 ◽  
Vol 1 ◽  
pp. 133-135
Author(s):  
Klaus Wieczorek ◽  
Katja Emmerich ◽  
Rainer Schuhmann ◽  
Jürgen Hesser ◽  
Markus Furche ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Host Rock ◽  
Large Scale ◽  
Excavation Damaged Zone ◽  
Rock Laboratory ◽  
Custom Made ◽  
Damaged Zone ◽  
Mont Terri ◽  
Mont Terri Rock Laboratory

Abstract. Shaft-sealing systems for nuclear waste repositories are constructed to limit fluid inflow from the adjacent rock during the early stage after closure of the repository and to delay the release of possibly contaminated fluids from the repository at later stages. Current German concepts of shaft seals contain the hydraulic sandwich sealing system as a component of the lower seal in host rock (Kudla and Herold, 2021). The KIT-developed sandwich sealing system consists of alternating sealing segments (DS) of bentonite and equipotential segments (ES) that are characterized by a high hydraulic conductivity. Within the ES, fluid is evenly distributed over the cross section of the seal. Water bypassing the seal via the excavation-damaged zone or penetrating the seal inhomogeneously is contained, and a more homogeneous hydration and swelling of the DS is obtained. The functionality of such a system was proven in laboratory and semi-technical-scale experiments (Schuhmann et al., 2009). After a joint international pre-project (Emmerich et al., 2019) dedicated to the planning of a large-scale in situ test that demonstrates the feasibility and effectiveness of the sandwich shaft-sealing system in interaction with the host rock, the large-scale experiment was launched at the Mont Terri rock laboratory in July 2019 with partners from Germany, Switzerland, Spain, UK, and Canada. It consists of two experimental shafts of 1.18 m diameter and 10–12.6 m depth, constructed using a core drilling technique with a custom-made drill rig in a new niche in the sandy facies of the Opalinus Clay. The seal in shaft 1 consists of four DS (calcigel) of 1 m thickness and five ES (fine-grained quartz sand), each 30 cm thick (Fig. 1). Shaft sinking began in August 2020 and was completed in November 2020. In the following months, the sealing system and instrumentation of shaft 1 were installed. The sealing system is saturated from a pressure chamber located at the shaft bottom via an inclined lateral feeding borehole. Hydration of the system started in May 2021. Shaft 2 will host a slightly modified system emplaced 1–1.5 years later, in order to integrate experience obtained during the early operation phase of shaft 1. In contrast to shaft 1, the excavation-damaged zone around shaft 2 will have had time to develop. The seals and the surrounding rock are intensely monitored. Measurements in the rock (geophysics, pore pressure, and total stress) were started between August 2019 and March 2020. Characterization of the excavation-damaged zone along the wall of shaft 1 was performed by geophysical and surface packer measurements prior to seal emplacement. Measurements inside the shaft comprise water content, relative humidity, and temperature, pore pressure, stress, and displacements. The in situ work is backed by laboratory testing and model simulation. Data and experience obtained to date will be presented. The sandwich experiment is funded by the German Federal Ministry for Economic Affairs and Energy under contract 02E11799.

CO2 data on gas and pore water sampled in situ in the Opalinus Clay at the Mont Terri rock laboratory

2008 ◽  
Vol 33 ◽  
pp. S54-S60 ◽  
Author(s):  
A. Vinsot ◽  
C.A.J. Appelo ◽  
C. Cailteau ◽  
S. Wechner ◽  
J. Pironon ◽  
...  
Keyword(s):  
Pore Water ◽  
Opalinus Clay ◽  
Rock Laboratory ◽  
Mont Terri ◽  
Mont Terri Rock Laboratory

Tiltmeter Measurements at the Underground Rock Laboratory in Mont Terri

2020 ◽  
Author(s):  
Dorothee Rebscher
Keyword(s):  
Decadal Variability ◽  
Opalinus Clay ◽  
Earthquake Activity ◽  
Rock Laboratory ◽  
In Situ Experiments ◽  
First Results ◽  
Mont Terri ◽  
Mont Terri Rock Laboratory

<p>Mont Terri rock laboratory, located in the Swiss Jurassic Mountains, was established with the focus on the investigation and analysys of the properties of argillaceous formations. The scope of Opalinus Clay as a safe, potential option for nuclear waste disposal was broaden, as the behaviour of claystone is of high interest also in the context of caprocks, and hence, for many dynamical processes in the subsurfaces. Extensive research has been performed already for more than 20 years by the partners of the Mont Terri Consortium. These close cooperations cover a broad range of scientific aspects using numerical modelling, laboratory studies, and last not least in-situ experiments. Here, included in the long-term monitoring programme, new investigations apply tiltmeters. Since April 2019, platform tiltmeters have been installed at various locations within the galleries and niches of Mont Terri. The biaxial instruments have resolutions of 1 nrad and 0.1 µrad, respectively (Applied Geomechanics and Lippmann Geophysikalische Messgeräte). The tilt measurements are embedded within various experiments contributing to specific, multiparametrical studies. However, the growing tilt network as a whole will also provide novel information of the rock laboratory. The different time-scales of interest include long-term observations of yearly and decadal variability. So far tilt signals were identified due to excavations during the recent enlargement of the laboratory, earthquake activity (Albania), and local effects. First results of these quasi-continuous recordings will be presented.</p>

scholarly journals Anisotropy of electrical conductivity of the excavation damaged zone in the Mont Terri Underground Rock Laboratory

2010 ◽  
Vol 181 (1) ◽  
pp. 303-320 ◽  
Author(s):  
Florence Nicollin ◽  
Dominique Gibert ◽  
Nolwenn Lesparre ◽  
Christophe Nussbaum
Keyword(s):  
Electrical Conductivity ◽  
Excavation Damaged Zone ◽  
Rock Laboratory ◽  
Damaged Zone ◽  
Mont Terri

scholarly journals Mechanical and hydraulic properties of the excavation damaged zone (EDZ) in the Opalinus Clay of the Mont Terri rock laboratory, Switzerland

Solid Earth ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 1581-1600
Author(s):  
Sina Hale ◽  
Xavier Ries ◽  
David Jaeggi ◽  
Philipp Blum
Keyword(s):  
Actual State ◽  
Fracture Aperture ◽  
Near Surface ◽  
Mechanical Fracture ◽  
Excavation Damaged Zone ◽  
Rock Laboratory ◽  
Hydraulic Aperture ◽  
Damaged Zone ◽  
Mont Terri

Abstract. Construction of cavities in the subsurface is always accompanied by excavation damage. Especially in the context of deep geological nuclear waste disposal, the evolving excavation damaged zone (EDZ) in the near field of emplacement tunnels is of utmost importance concerning safety aspects. As the EDZ differs from the intact host rock due to enhanced hydraulic transmissivity and altered geomechanical behavior, reasonable and location-dependent input data on hydraulic and mechanical properties are crucial. Thus, in this study, a hydromechanical characterization of an EDZ in the Mont Terri underground rock laboratory, Switzerland, was performed using three different handheld devices: (1) air permeameter, (2) microscopic camera and (3) needle penetrometer. The discrete fracture network (DFN), consisting of artificially induced unloading joints and reactivated natural discontinuities, was investigated by a portable air permeameter and combined microscopic imaging with automatic evaluation. Geomechanical and geophysical characterization of the claystone was conducted based on needle penetrometer testing at the exposed rock surface. Within the EDZ, permeable fractures with a mean hydraulic aperture of 84 ± 23 µm are present. Under open conditions, self-sealing of fractures is suppressed, and cyclic long-term fracture aperture oscillations in combination with closure resulting from convergence processes is observed. Based on measured needle penetration indices, a uniaxial compressive strength of 30 ± 13 MPa (normal to bedding) and 18 ± 8 MPa (parallel to bedding) was determined. Enhanced strength and stiffness are directly related to near-surface desaturation of the claystone and a sharp decrease in water content from 6.6 wt % to 3.7 wt %. The presented methodological approach is particularly suitable for time-dependent monitoring of EDZs since measurements are nondestructive and do not change the actual state of the rock mass. This allows for a spatially resolved investigation of hydraulic and mechanical fracture apertures, fracture surface roughness, and physico-mechanical rock parameters and their intra-facies variability.

scholarly journals Concept of Large-scale Thermomechanical URL Experiments in the Nizhnekanskiy Rock Massif

2020 ◽  
Vol 12 (3) ◽  
pp. 101-111
Author(s):  
E. V. Moiseenko ◽  
◽  
N. I. Drobyishevsky ◽  
R. A. Butov ◽  
Yu. N. Tokarev ◽  
...  
Keyword(s):  
Host Rock ◽  
Large Scale ◽  
Mutual Influence ◽  
Thermomechanical Properties ◽  
Coupled Processes ◽  
Small Scale ◽  
Initial State ◽  
Excavation Damaged Zone ◽  
Damaged Zone ◽  
Engineered Barriers

Numerical simulation of thermomechanical processes in a deep underground radioactive waste repository requires information on the host rock and the engineered barriers properties at a scale of dozens of centimeters, meters and more. However, the extrapolation of the values obtained on small-scale samples in surface laboratories yields excessive uncertainties. The materials behavior is also influenced by conditions that cannot be reliably reproduced in a surface laboratory, such as water content or initial stress-strain state. Following experiments are planned to study the host rock and the engineered barriers behavior during heating under conditions similar to those expected in the repository, as well as to assess their large-scale thermomechanical properties. In the experiment focused on the excavation damaged zone thermal mechanics, the behavior of reinforced drift walls and vaults under heating will be studied. The experimental facility will involve two drifts with the same orientation as the planned repository ones. As a result, the spatial distribution of excavation damaged zone thermomechanical parameters and their evolution due to heating will be identified. The second experiment focuses on the host rock mass behavior under spatially nonuniform unsteady heating. The facility will feature two vertical boreholes with heaters. The experiment will be divided into several stages: study of the host rock initial state, estimation of the rock main thermomechanical properties, study of the temporal evolution of the stress field due to 3D temperature gradients and of the processes in the host rock occurring during its cooling and re-saturation with water. Following the completion of the separate-effect test program, an integrated experiment should be carried out to study the coupled processes with respect to their mutual influence. The obtained results will be used to refine the values of input parameters for numerical simulations and their uncertainty ranges, as well as to validate the computer codes.

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