scholarly journals Geophysical estimation of the damage induced by an observatory digging in a limestone heterogeneous vadose zone – Beauce aquifer (France)

2020 ◽  
Author(s):  
Céline Mallet ◽  
Clara Jodry ◽  
Gautier Laurent ◽  
Mohamed Azaroual
Keyword(s):  
Host Rock ◽  
Water Saturation ◽  
Point Of View ◽  
Time Variability ◽  
Heterogeneous Structure ◽  
Saturation State ◽  
Magnetic Resonance Sounding ◽  
Damaged Zone ◽  
Fractured Limestone ◽  
Initial Zone

<p>The O-ZNS observatory offers a unique geophysical support for characterization, at different scales (from nano- to metric scales) of the heterogeneous Beauce Limestones aquifer. Currently under development at an agricultural site in Villamblain (Centre Val de Loire, France), this observatory is based on an exceptional well (20 m-depth and 4 m-diameter) associated with many external boreholes on an area of around 2 400 m<sup>2</sup>. It will combine different geophysical techniques and innovative multi-geosciences sensors to image, monitor and understand fluid and heat transfers in the heterogeneous structure of the vadoze zone.</p><p>An initial geophysical characterization has been conducted with surface measurements (3D electrical resistivity imaging and 2D Magnetic Resonance Sounding) that gave interesting information on the lithology of O-ZNS site: a silty-clayed soil of a few meter thick, then a highly heterogeneous and karstified limestone and finally, the massive fractured limestone. Cross-hole radar measurements add to these information a description of the initial zone, the soil properties and the water content. Also, data from three boreholes and the collection of core samples as well as logging measurements completed and improved this initial characterization.</p><p>All these data have been used to develop a finite element numerical model representing both the study site and the well under Plaxis 2D. Through the realism of geotechnical engineering including deformation, stability and water flow, the idea, is to anticipate the effect of the digging and provide information about the induced damaged zone that will derive. We also look into describing the evolution of this damaged zone depending on the seasoning variation (i.e. from 3 to 5 m) of the groundwater level. All these characterizations will allow us to better focus our field geophysical investigations on monitoring the damaged zone.</p><p>The model consists of a description of the different soil layers from the boreholes that includes elastic, microstructural and transport properties, followed by a description of the interface between the soil and the well. The hydraulic conditions will take into account the time-variability of fluxes and the aquifer level. Furthermore, this model is coupled with the construction phasing from a civil engineering point of view. The results will give the evolution of stress and strain induced by the engineering development of O-ZNS well in the host rock as well as an estimate of the material displacement and its elasticity limits. The preliminary modelling generated a result stipulating a damaged zone of 1-2 m around the well at the surface. The magnitude of the damaged zone is reduced with depth. It seems that, at the bottom, the host rock is undamaged.</p><p>Undergoing development are focused on refining the model by providing more effective and updated estimations of the soil and structure properties in order to validate or improve the first results together with an estimation of the time evolution of the damaged zone with the water saturation state. Afterward, we will be able to compare and validate these results to pictures and measurements performed during the digging that will start in the spring 2020.</p>

THM analysIs of natural and engineered barriers for large excavations in deep nuclear waste repository

2021 ◽  
Author(s):  
Matias Alonso ◽  
Jean Vaunat ◽  
Minh-Ngoc Vu ◽  
Antonio Gens
Keyword(s):  
Nuclear Waste ◽  
Host Rock ◽  
Thermal Load ◽  
Water Pressure ◽  
Large Diameter ◽  
Coupled Processes ◽  
Nuclear Waste Repository ◽  
Damaged Zone ◽  
Waste Repository ◽  
The Impact

<p>Argillaceous rocks have great potential as possible geological host medium to store radioactive waste.  Andra is leading the design of a deep geological nuclear waste repository to be located in the Callovo-Oxfordian formation. In the framework of this project, excavations of large diameter galleries are contemplated to access and to store intermediate-level long-lived nuclear waste at repository main level. The closure of the repository will be realized by building sealing structures of expansive material.</p><p>The response of such structures is affected by several thermo-hydro-mechanical coupled processes taking place in the near and far field of the argillaceous formations. They include the formation of an excavation induced damaged zone around the galleries, the impact of the thermal load on host rock pressures and deformations, the long-term interaction with support concrete structural elements and the hydration and swelling of sealing materials. As a result, the study of their performance requires to perform simulation works of increasing complexity in terms of coupling equations, problem geometry and material behaviour. As well, challenging computational aspects, as the ones related to fractures creation and propagation, have to be considered for a representative analysis of the problem.</p><p>This work presents advanced large scale THM numerical models to provide keys about the response of the host rock around large diameter galleries during excavation and further thermal load as well as to analyse the performance of large diameter sealing structures. Particular features of the models include on one hand advanced constitutive laws to capture the development of the fractured zone around excavations, the behaviour of host rock/gallery support interfaces and the multi-scale response of bentonitic backfill. On the other hand, simulations consider geometries including constructive details of interest at decimetre scale within large discretization domain covering the whole formation stratigraphic column.</p><p>These challenging simulations provided qualitative and quantitative results on key aspects for natural and engineered barrier integrity, like extension of the damaged zone, impact of the thermal load and water pressure variations in the surrounding geological layers, duration of natural hydration phase, swelling pressure development and seals global stability.</p>

Hydro-geochemical processes in the emplacement cavern of a low and intermediate-level waste repository in an indurated clay-rock

2021 ◽  
Author(s):  
Vanessa Montoya ◽  
Jaime Garibay-Rodriguez ◽  
Olaf Kolditz
Keyword(s):  
Chemical Evolution ◽  
Nuclear Waste ◽  
Host Rock ◽  
Numerical Models ◽  
Intermediate Level ◽  
High Level Waste ◽  
Nuclear Waste Repository ◽  
Case Scenario ◽  
Damaged Zone ◽  
Waste Repository

<p>By 2080, Germany will have to store around 600 000 m<sup>3</sup> of low and intermediate-level nuclear waste (L-ILW) with negligible heat generation. This kind of waste is largely made up of used parts of nuclear power stations such as pumps, pipelines, filters, etc. placed in various types of waste containers made from either steel, cast iron, or reinforced concrete in different designs and sizes (i.e. cylindrical or box shaped). It is already decided that a total of 303 000 of the 600 000 m<sup>3</sup> L-ILW will be disposed in a final storage facility in the former iron ore mine Schacht Konrad which is under construction. However, it is still not clear where the L-ILW emplaced in in the old salt mine Asse (200 000 m<sup>3</sup>) will be stored in the future. The situation is particularly critical, as the waste have to be retrieved from the instable mine shafts partially flooded with groundwater, causing strong socio-political concerns as radioactive waste could contaminate the water nearby. For this reason, the new search for a nuclear waste repository for high-level waste (HLW), started in 2017, should also consider the possibility to accommodate the waste from Asse. Obviously, this is still subject to critics as this will make finding a final repository more difficult as storing HLW and L-ILW together requires different concepts and designs for each other and, above all, much more space.</p><p>In this context, in this contribution we have defined conceptual and numerical models to assess the hydro-chemical evolution of a L-ILW disposal cell in indurated clay rocks, involving the interaction of different components/materials and the expected hydraulic and/or chemical gradients over 100 000 years. The L-ILW disposal cell leverages a multi-barrier concept buried 400 m below the surface. The multi-barrier system is comprised of the waste matrix (i.e. backfilling the waste drums), the disposal container, the mortar backfill in the emplacement tunnel (where the disposal containers are located) and the clay host rock. The dimensions and design of the emplacement tunnel (e.g. 11 × 13 m) and disposal cells represent and consider some aspects taken into account in the designs of some European countries. In addition, tunnel walls reinforced with a shotcrete liner and the Excavation Damaged Zone is considered in the concept. The model is implemented in OpenGeoSys-6, an open-source version-controlled scientific software based on Finite Element Method which is capable of handling fully coupled hydro-chemical models by coupling OpenGeoSys to iPHREEQC. First calculation results, demonstrate that the most important processes affecting the near-field chemical evolution are i) the degradation of the concrete and cementitious grouts with porewater migrating inwards from the host rock and ii) the significant quantities of reactive and non-reactive gases (i.e. hydrogen, carbon dioxide and methane) that are generated as a result of: i) the anaerobic corrosion of metals present in the waste and containers and ii) the degradation of organic compounds by microbial and chemical processes. As a first approximation, some assumptions and simplifications have been considered, probably resulting in a wort case scenario.</p>

scholarly journals Influence of Humidity on the Elastic Modulus and Axis Compressive Strength of Concrete in a Water Environment

Materials ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 5696
Author(s):  
Guohui Zhang ◽  
Changbing Li ◽  
Hai Wei ◽  
Mingming Wang ◽  
Zhendong Yang ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Elastic Modulus ◽  
Water Saturation ◽  
Water Environment ◽  
Systematic Research ◽  
Saturation State ◽  
Soaking Time ◽  
Axial Compressive Strength ◽  
Saturated Concrete ◽  
Compressive Strength Of Concrete

Concrete structures are often in different humidity conditions that have a significant impact on the elastic modulus of concrete, therefore, systematic research on the evolution of the law of concrete elastic modulus under different humidity conditions is needed. In this study, the variation laws of the water saturation of concrete specimens with strength grades C15, C20, and C30 were obtained, and then the influence laws of the water saturation on the concrete axial compressive strength were carried out, and the prediction model of elastic modulus of concrete with respect to water saturation was constructed. The results showed that the water saturation of concrete with strength grades C15, C20, and C30 increased with an extension of immersion time, and the water saturation showed an approximately linear rapid growth within three soaking hours, reaching 47.56%, 71.63%, and 47.29%, respectively. Note, the concrete reached saturation state when the soaking time was 240 h. The axial compressive strength with strength grades C15, C20, and C30 decreased with increased water saturation, and the axial compressive strength of saturated concrete decreased by 27.25%, 21.14%, and 20.76%, respectively, as compared with the dry state concrete. The elastic modulus of concrete with strength grades C15, C20, and C30 increased with increased water saturation, and the elastic modulus of saturated concrete was 1.18, 1.19, and 1.24 times higher than those of dry concrete, respectively.

scholarly journals Influence of the Saturation Ratio on Concrete Behavior under Triaxial Compressive Loading

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Xuan-Dung Vu ◽  
Matthieu Briffaut ◽  
Yann Malecot ◽  
Laurent Daudeville ◽  
Bertrand Ciree
Keyword(s):  
Nuclear Power ◽  
Water Saturation ◽  
Confining Pressure ◽  
Degree Of Saturation ◽  
Triaxial Tests ◽  
Saturation Ratio ◽  
Concrete Wall ◽  
Saturation State ◽  
Massive Concrete ◽  
The Impact

When a concrete structure is subjected to an impact, the material is subjected to high triaxial compressive stresses. Furthermore, the water saturation ratio in massive concrete structures may reach nearly 100% at the core, whereas the material dries quickly on the skin. The impact response of a massive concrete wall may thus depend on the state of water saturation in the material. This paper presents some triaxial tests performed at a maximum confining pressure of 600 MPa on concrete representative of a nuclear power plant containment building. Experimental results show the concrete constitutive behavior and its dependence on the water saturation ratio. It is observed that as the degree of saturation increases, a decrease in the volumetric strains as well as in the shear strength is observed. The coupled PRM constitutive model does not accurately reproduce the response of concrete specimens observed during the test. The differences between experimental and numerical results can be explained by both the influence of the saturation state of concrete and the effect of deviatoric stresses, which are not accurately taken into account. The PRM model was modified in order to improve the numerical prediction of concrete behavior under high stresses at various saturation states.

scholarly journals Accelerating universe and the time-dependent fine-structure constant

2009 ◽  
Vol 5 (H15) ◽  
pp. 302-302
Author(s):  
Yasunori Fujii
Keyword(s):  
Fine Structure ◽  
Scalar Field ◽  
Structure Constant ◽  
Theoretical Background ◽  
Point Of View ◽  
Fine Structure Constant ◽  
Time Variability ◽  
Accelerating Universe ◽  
Tensor Theory ◽  
The Right

I start with assuming a gravitational scalar field as the dark-energy supposed to be responsible for the accelerating universe. Also from the point of view of unification, a scalar field implies a time-variability of certain “constants” in Nature. In this context I once derived a relation for the time-variability of the fine-structure constant α: Δα/α =ζ Ƶ(α/π) Δσ, where ζ and Ƶ are the constants of the order one, while σ on the right-hand side is the scalar field in action in the accelerating universe. I use the reduced Planckian units with c=ℏ =MP(=(8π G)−1/2)=1. I then compared the dynamics of the accelerating universe, on one hand, and Δα/α derived from the analyses of QSO absorption lines, Oklo phenomenon, also different atomic clocks in the laboratories, on the other hand. I am here going to discuss the theoretical background of the relation, based on the scalar-tensor theory invented first by Jordan in 1955.

scholarly journals Kafka’s animals between mimicry and assimilation

2019 ◽  
Vol 9 (3-4) ◽  
pp. 159-167
Author(s):  
Barbara Di Noi
Keyword(s):  
Gustave Flaubert ◽  
Point Of View ◽  
The Self ◽  
Heterogeneous Structure ◽  
Small Animals ◽  
The Subject

Abstract In Kafka’s literary world, several animals emerge; they belong to an odd and enigmatic fauna, on the edge between violence and artistry but also between stillness and music; according to the writer, scripture represents both the fault and the punishment waiting for the solitary artist. Animals, especially depicted as hordes of small mice or other rodents, also hint to the heterogeneous structure of the Self, who doesn’t manage to keep under control all the divisions in his ambiguous dentity. Through opposition between the point of view of the subject, who considers his own isolation as indispensable to carry on writing, and the multitude of escaping small animals, Kafka also expresses and experiences his own impossibility of “description” (Beschreibung). In the meantime, Kafka’s animals embody the creatural and unconscious sources of imagination the writer draws from that constantly escape his own control and willingness, pushing forwards into an unknown and inhospitable region, towards the wasteland, the eternal winter that can be identified with scripture. In writing, a deep metamorphosis of the Self takes place. Kafka shares this belief with one of the writers he most admired and considered his master, Gustave Flaubert, who firmly thought that, while writing, one loses his previous identity, becoming someone else, even assuming the appearence of the “otherness”. We can state that Kafka’s imagery of animals takes to the extreme the paradox and ambiguity the idea of writing relies on, also reproducing, especially, in his hybrid creatures, the feeling of uncertainty and lack of safety of the assimilated Jewish artist.

Technique Proves Effective in Remediation of Phase-Trapping Damage in Tight Reservoirs

2021 ◽  
Vol 73 (07) ◽  
pp. 60-61
Author(s):  
Chris Carpenter
Keyword(s):  
Chemical Treatment ◽  
Water Saturation ◽  
Gas Permeability ◽  
Abu Dhabi ◽  
Absolute Permeability ◽  
Treatment Technique ◽  
The Core ◽  
Carbonate Formation ◽  
Irreducible Water Saturation ◽  
Damaged Zone

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202996, “An Efficient Treatment Technique for Remediation of Phase-Trapping Damage in Tight Carbonate Gas Reservoirs,” by Rasoul Nazari Moghaddam, SPE, Marcel Van Doorn, and Auribel Dos Santos, SPE, Nouryon, prepared for the 2020 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, held virtually 9–12 November. The paper has not been peer reviewed. Aqueous- and hydrocarbon-phase trapping are among the few formation-damage mechanisms capable of significant reduction in effective permeability (sometimes near 100%). In this study, a new chemical treatment is proposed for efficient remediation of water- or hydrocarbon-phase-trapping damage in low-permeability porous media. The method proposed here is cost-effective and experimentally proved to be efficient and long-lasting. Such a chemical treatment is recommended to alleviate gas flow in tight gas with aqueous-trapping-damaged zones or in gas condensate reservoirs with condensate-banking challenges. Introduction Remediation techniques for existing aqueous- or hydrocarbon-phase-trapping damage can be categorized into two approaches: bypassing the damaged region by direct penetration techniques and trapping-phase removal. In the former category, the damaged zone is bypassed by creation of high-conductance flow paths through hydraulic fracturing or acidizing. However, for tight and ultratight formations, conventional acidizing may not be feasible (mostly because of injectivity difficulties). In the second category, direct removal and indirect removal have been used, but usually are seen as short-term solutions. The fluid used in the proposed treatment is comprised of a nonacidic chelating agent. The treatment fluid can be injected safely into the damaged region, while a slow reaction rate allows it to penetrate deep into the formation. In the proposed treatment, the mechanism is the permanent enlargement of pore throats where the nonwetting phase has the most restriction (to overcome the capillary forces) to pass through. In fact, phase trapping or capillary trapping occurs inside the pore structure when viscous forces are not strong enough to overcome the capillary pressure. The experimental setup and method are detailed in the complete paper. Results and Discussion Treatment of Outcrop Samples: Lueder Carbonate. The performance of the proposed treatment fluid initially was investigated on two outcrop core samples from the Lueder carbonate formation. The first treatment was conducted on the Le1 core sample with an absolute permeability of 1.46 md. To establish trapped water in the core, 10 pore volumes (PV) of 5 wt% potassium chloride brine were injected followed by nitrogen (N2) gas displacement. Then, to achieve irreducible water saturation, N2 was injected at a rate of 2 cm3/min for at least 100 PVs until no further water was produced. Next, the effective gas permeability was measured while N2 was injected at approximately 0.2 cm3/min. The effective gas permeability was obtained as 0.042 md. The trapped water saturation was also calculated (from the core weight) as 77.7%. After all pretreatment measurements, the core was loaded into the core holder for the treatment. The treatment injections with preflush and post-flush were performed at 130°C. In this test, 0.5 PV of treatment fluid was injected.

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.

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.

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