Gas flow in Callovo-Oxfordian claystone (COx): results from laboratory and field-scale measurements

AbstractTo understand the fate and impact of gas produced within a repository for radioactive waste, a series of laboratory and field scale experiments have been performed on the Callovo-Oxfordian claystone (COx), the proposed host rock for the French repository. Results show the movement of gas is through a localized network of pathways, whose properties vary temporarily and spatially within the claystone. Significant evidence exists from detailed laboratory studies for the movement of gas along highly unstable pathways, whose aperture and geometry vary as a function of local stress, gas and porewater pressures. The coupling of these parameters results in the development of significant time-dependent effects, impacting on all aspects of COx behaviour, from gas breakthrough time, to the control of deformation processes. Variations in gas entry, breakthrough and steady-state pressures are indicative of microstructural heterogeneity which exerts an important control on the movement of gas. The localization of gas flow is also evident in preliminary results from the large scale gas injection test (PGZ) where gas flow is initially focussed within the excavation damaged zone (EDZ), which acts as a preferential pathway for gas. Numerical models based on conventional two-phase flow theory are unable to adequately describe the detailed observations from laboratory tests.

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Modelling of water and gas flow through an excavation damaged zone in the Callovo-Oxfordian argillites in the framework of a single porosity model

Geological Society London Special Publications ◽

10.1144/sp443.6 ◽

2016 ◽

Vol 443 (1) ◽

pp. 319-332 ◽

Cited By ~ 3

Author(s):

Luc-Vincent Bénet ◽

Étienne Blaud ◽

Jacques Wendling

Keyword(s):

Gas Flow ◽

Excavation Damaged Zone ◽

Damaged Zone ◽

Flow Through ◽

Porosity Model

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Gas Flow Through Water-Saturated Shear Zones: Field and Laboratory Experiments and Their Interpretation

MRS Proceedings ◽

10.1557/proc-506-741 ◽

1997 ◽

Vol 506 ◽

Cited By ~ 1

Author(s):

P. Marschall ◽

J. Croisé ◽

U. Fischer ◽

R. Senger ◽

E. Wyss

Keyword(s):

Shear Zone ◽

Gas Flow ◽

Two Phase Flow ◽

Gas Permeability ◽

Numerical Models ◽

Shear Zones ◽

Parameter Estimates ◽

Phase Flow ◽

Two Phase ◽

Flow Processes

ABSTRACTGas threshold pressure tests and gas tracer tests have been performed at the Grimsel Test Site to study two-phase flow processes in a shear zone. In addition, capillary pressure and gas permeability measurements were carried out in the laboratory on drillcore samples. The laboratory investigations were complemented by assessing the pore structure of the shear zone material. The interpretation of the field tests with numerical models indicated that the structural and two-phase flow parameters to be determined are highly correlated with one another and, consequently, the parameter estimates can be rather uncertain. The joint interpretation of field and laboratory results, however, led to a more stringent description of the two-phase flow processes, expressed by a better overall fit of the test data and smaller uncertainty ranges of the estimated parameters. The results showed that the gas mobility in the shear zone was very high even at high water saturation and gas flow was limited to the narrow zones of brittle deformation along the shear zone.

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

Radioactive waste ◽

10.25283/2587-9707-2020-3-101-111 ◽

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

Safety of Nuclear Waste Disposal ◽

10.5194/sand-1-133-2021 ◽

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.

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Demonstration of Gas-Permeable Seals for Radioactive Waste Repositories: Laboratory and In-Situ Experiments

ASME 2011 14th International Conference on Environmental Remediation and Radioactive Waste Management, Parts A and B ◽

10.1115/icem2011-59224 ◽

2011 ◽

Cited By ~ 1

Author(s):

Joerg Rueedi ◽

Paul Marschall

Keyword(s):

Radioactive Waste ◽

Large Scale ◽

Gas Flow ◽

Two Phase Flow ◽

Gas Transport ◽

Phase Flow ◽

Transport Capacity ◽

Underground Structures ◽

Two Phase ◽

National Cooperative

In low/intermediate-level waste (L/ILW) repositories, anaerobic corrosion of metals and degradation of organic materials produce hydrogen, methane, and carbon dioxide. Gas migration in a L/ILW repository is one of the processes evaluated in the safety assessment of deep geological disposal in low-permeability formations, in particular with respect to the development of gas pressures in the repository caverns which could negatively affect the host rock or the engineered barrier system (EBS). In order to restrict build-up of gas overpressures in the emplacement caverns, Nagra (National Cooperative for the Disposal of Radioactive Waste, Switzerland) has proposed design options aimed at increasing the gas transport capacity of the backfilled underground structures, compromising neither the low hydraulic conductivity nor the radionuclide retention capacity of the EBS (Nagra, 2008). They involve specially designed backfill and sealing materials such as high porosity mortars as backfill materials for the emplacement caverns and sand/bentonite (S/B) mixtures with a bentonite content of 20% to 30% for the seals themselves and for backfilling other underground structures. These increased gas permeability materials can supplement the gas flow that is expected to occur through the excavation damaged zone (EDZ) and avoid the creation of overpressures. Preliminary experimental studies have confirmed the gas transport capacity of the S/B mixtures and demonstrated the ability to design mixtures with specific target permeabilities for water and gas flow (Nagra, 2008). Two-phase flow modelling studies have shown that the gas transport capacity of seals is largely dependent on their permeability and length. More detailed models of sealing elements show a rather complex history of seal saturation during the early saturation phase and the later gas escape phase (Gaus et al., 2010). Note, however, that current modelling approaches are based on parameters and conceptual understanding of small-scale laboratory experiments. Two large(r) scale experiments which aim at validating and, if necessary, improving current conceptual models for the resaturation and gas invasion processes into S/B seals and the determination of up-scaled gas / water permeabilities of S/B seals (i.e. two-phase flow parameters for large-scale models) have been initiated and will be highlighted in the paper. The first one, a mock-up experiment, was set up in 2010 as part of the EU 7th FP project FORGE, aiming at demonstrating seal performance on an intermediate (decimetre scale). The second one is a large-scale experiment (metre-scale), the Gas-Permeable Seal Test (GAST), which was also initiated in 2010 at the Grimsel Test Site (GTS). For GAST, a seal will be emplaced at the GTS to demonstrate the effective functioning of gas-permeable seals on a realistic scale and with realistic boundary conditions (‘proof of concept’).

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Research Progress of Initial Mechanism on Debris Flow and Related Discrimination Methods: A Review

Frontiers in Earth Science ◽

10.3389/feart.2021.629567 ◽

2021 ◽

Vol 9 ◽

Author(s):

Jun Du ◽

Zhong-jie Fan ◽

Wen-tao Xu ◽

Lin-yao Dong

Keyword(s):

Debris Flow ◽

Large Scale ◽

Numerical Models ◽

Soil Mass ◽

Assessment Method ◽

Research Progress ◽

Two Phase ◽

Indicator Method ◽

Technical Limitation ◽

Debris Flow Initiation

The initial of debris flow can be classified into two types based on their triggering positions, that is, debris flow from slope and debris flow from gully or channel. For the former, great progress has been achieved on the mechanisms of soil failure and liquefaction. The framework established by a series of theories or laws, such as the Mohr–Coulomb criteria, the unsaturated soil mechanics, and the critical state of soil mass, has been used widely in industry and research. However, the details and discrimination basis for the transformation process from landslide into debris flow still need to be further clarified. Relatively, debris flow from gully or channel is more complex due to its various mass sources and the diversity of processes. Nevertheless, through a great number of case studies and experimental statistics, people have gradually recognized the influential rule and critical condition of factors from landform, hydrology, and other aspects on debris flow initiation. Furthermore, based on the theories of granular flow, continuum mechanics, and rheological law, some typical event-based scenarios can also be reproduced by different single-/two-phase depth integral/average numerical models. However, some key knowledge on mechanism and application level is still insufficient, such as the erosion and entrainment mechanism of materials from different sources, the boundary tractions and materials exchange, as well as the selection of prediction indicators. Three current discriminated methodologies for debris flow initiation, that is, the safety factor method, the rainfall indicator method, and the comprehensive assessment method, were summarized in this article. Considering the technical limitation of each methodology, it is believed that the establishment or improvement of a unified, stable, and open-access database system for event registration and query, as well as the development of large-scale and high-precision rainfall monitoring, is still regarded as the important aspect of debris flow prevention in the future. In addition, as an economic and efficiency means for obtaining information on potential threats and real-time hazard messages, the multielement method for debris flow is recommended as a long-term reference.

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Numerical Simulation of Condensed Water Behavior in Gas Diffusion Layers of PEFC Using the Lattice Boltzmann Method

ASME 2013 11th International Conference on Nanochannels, Microchannels, and Minichannels ◽

10.1115/icnmm2013-73111 ◽

2013 ◽

Author(s):

Yutaka Tabe ◽

Ryuji Kamijo ◽

Yuji Honjo ◽

Kengo Suzuki ◽

Takemi Chikahisa

Keyword(s):

Lattice Boltzmann Method ◽

Liquid Water ◽

Lattice Boltzmann ◽

Large Scale ◽

Gas Flow ◽

Gas Diffusion ◽

Two Phase ◽

Water Behavior ◽

Condensed Water ◽

Boltzmann Method

Numerical simulations using the lattice Boltzmann method (LBM) has been developed to elucidate the dynamic behavior of condensed water in a gas diffusion layer (GDL) of a polymer electrolyte membrane fuel cell (PEFC). Here, a LBM model of two-phase flow with equal densities was applied, because the condensed water behavior is less affected by the gas flow. The simulation results showed that the LBM applied here can simulate dynamic capillary fingering at low migration speeds of liquid water in a GDL, which is similar to the results of the LBM simulation with large density differences. Using the equal density LBM, we conducted efficient large-scale analyses to elucidate the effect of the GDL structure and wettability on the liquid water behavior inside of the GDL.

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Modelling the multiscale behaviour of claystone: deformation, rupture, and hydro-mechanical phenomena around underground galleries

E3S Web of Conferences ◽

10.1051/e3sconf/202020510003 ◽

2020 ◽

Vol 205 ◽

pp. 10003

Author(s):

Benoît Pardoen ◽

Frédéric Collin ◽

Pierre Bésuelle ◽

Robert Charlier ◽

Jean Talandier ◽

...

Keyword(s):

Large Scale ◽

Flow Characteristics ◽

Small Scale ◽

Underground Engineering ◽

Engineering Structures ◽

Excavation Damaged Zone ◽

Damaged Zone ◽

Scale Characteristics ◽

High Level ◽

Double Scale

In the context of underground exploitation, the behaviour of rocks near galleries and tunnels conditions their stability. Underground drilling generates deformations, damage, fracturing, and significant modification of flow characteristics in the surrounding rock. However, the influence of small-scale characteristics and behaviour on the rock deformations and damage at engineering scale remains a complex issue. Consequently, the multiscale behaviour of a clay rock is modelled starting from the large scale of the excavation damaged zone around galleries and then enriching the approach by considering microstructural characteristics from the scale of mineral inclusions. Lastly, a double-scale numerical framework is considered. It allows to relate small- to large-scale rock behaviour in terms of deformations and material rupture. In fact, the development of damage and cracking at microscale allows to predict large-scale fracturing. The developed method focuses on a claystone in the particular context of long-term management of high-level nuclear wastes by deep geological repository. The results highlight the possibilities of double-scale computing in the prediction of the behaviour of underground engineering structures.

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The Numerical Simulation of Hard Rocks for Tunnelling Purposes at Great Depths: A Comparison between the Hybrid FDEM Method and Continuous Techniques

Advances in Civil Engineering ◽

10.1155/2018/3868716 ◽

2018 ◽

Vol 2018 ◽

pp. 1-18 ◽

Cited By ~ 5

Author(s):

Nicholas Vlachopoulos ◽

Ioannis Vazaios

Keyword(s):

Numerical Models ◽

Fracture Initiation ◽

Fracture Network ◽

Complex Nature ◽

Underground Opening ◽

Hard Rocks ◽

Excavation Damaged Zone ◽

Damaged Zone ◽

Stress Changes ◽

Element Method

Tunnelling processes lead to stress changes surrounding an underground opening resulting in the disturbance and potential damage of the surrounding ground. Especially, when it comes to hard rocks at great depths, the rockmass is more likely to respond in a brittle manner during the excavation. Continuum numerical modelling and discontinuum techniques have been employed in order to capture the complex nature of fracture initiation and propagation at low-confinement conditions surrounding an underground opening. In the present study, the hybrid finite-discrete element method (FDEM) is used and compared to techniques using the finite element method (FEM), in order to investigate the efficiency of these methods in simulating brittle fracturing. The numerical models are calibrated based on data and observations from the Underground Research Laboratory (URL) Test Tunnel, located in Manitoba, Canada. Following the comparison of these models, additional analyses are performed by integrating discrete fracture network (DFN) geometries in order to examine the effect of the explicit simulation of joints in brittle rockmasses. The results show that in both cases, the FDEM method is more capable of capturing the highly damaged zone (HDZ) and the excavation damaged zone (EDZ) compared to results of continuum numerical techniques in such excavations.

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