Excavation Disturbed Zone Research Articles

Two-Phase Flow Modeling with Tough2-Mp of a Deep Geological Repository Within the First Benchmark of the FORGE Project

FORGE (Fate of Repository Gases) is an international research project supported by funding under the European Commission FP7 Euratom program and lasting four years from 2009 to 2013. The project is dedicated to understanding gas generation and migration as part of the quantitative assessment of a geological repository for radioactive waste. Within the FORGE project, Work Package 1 is dedicated to numerical modeling of a two-phase flow system (hydrogen gas due to corrosion and groundwater) in a geological repository for radioactive waste. Several benchmark exercises were proposed that cover the modeling of a deep geological repository from the disposal cell scale to the repository scale with different codes. During the definition of the exercises, special emphasis was given to the roles of the excavation-disturbed zone and of the interfaces between materials, which could act as a conduit for preferential flow. Some changes were made in the TOUGH2 code to enable the implementation of the prescribed conditions, models, and parameters of the benchmark. The results of the calculations performed with different codes show that TOUGH2 gives comparable results under the numerically challenging conditions defined in the exercise. Some differences were observed resulting from the use of different codes and also from some simplifications in the parameters and models adopted by the participating teams. In this paper, the cell-scale benchmark exercise and the results obtained by the Swiss Federal Nuclear Safety Inspectorate (ENSI) with TOUGH2 will be described, together with some difficulties encountered during the simulation, e.g., convergence problems. The results of other teams participating in the benchmark are in good agreement with the ENSI results.

Development and applications of rock fracture mechanics modelling with FRACOD: a general review

Rock failure is often controlled by fracture initiation, propagation and coalescence, especially in hard rocks where explicit fracturing rather than plasticity is the dominant mechanism of failure. Prediction of the explicit fracturing process is therefore necessary when the rock mass stability is investigated for engineering purposes. However, the fracture mechanics approach is rarely used in practical rock engineering design partly due to the inadequate understanding of complex fracturing processes in jointed rock mass and partly due to the lack of tools which can realistically predict the complex fracturing phenomenon in rock mass. Since 1990s, a new approach to simulating rock mass failure problems has been developed using a numerical code namely FRACOD. FRACOD is a code that predicts the explicit fracturing process in rocks using fracture mechanics principles. Over the past three decades, significant progress has been made in developing this approach to a level that it can predict actual rock mass stability at an engineering scale. The code includes complex coupling processes between the rock mechanical response and thermal process and hydraulic flow, making it possible to handle coupled problems often encountered in geothermal, hydraulic fracturing, nuclear waste disposal and underground Liquefied Natural Gas (LNG) storage. During this period, numerous application cases have been conducted using FRACOD, which includes: borehole stability in deep geothermal reservoir, pillar spalling under mechanical and thermal loading; prediction of tunnel and shaft stability and excavation disturbed zone, etc. This paper summarises the theoretical fundamentals of the fracture mechanics approach with FRACOD and the most recent developments. Several selected application cases are also discussed briefly in this paper to demonstrate the effectiveness of this approach.

Poromechanical response of borehole in excavation disturbed zone

This paper presents time-dependent response of a cylindrical borehole in a poroelastic medium with an excavation disturbed zone. The general solutions are derived based on Biot’s theory of poroelasticity by employing Laplace and Fourier transforms. Both shear modulus and permeability coefficient are assumed to be changed from their original values in the disturbed zone. The general solutions are employed to formulate boundary value problems corresponding to a borehole subjected to axisymmetric loading applied at its surface, and contact problems of a rigid cylindrical plug in a borehole. Selected numerical results are presented to portray the influence of poroelastic effects and the excavation disturbed zone.

Ultrasonic sounding and monitoring of the excavation damaged zone in relation with drift support

Under high in situ stresses, the excavation of underground openings generally causes the creation of a disturbed (EdZ: Excavation disturbed Zone) and/or damaged (EDZ: Excavation Damaged Zone) zone, resulting from the initiation and growth of cracks and fractures and from the pre-existing stress redistribution. The EdZ or EDZ changes the mechanical and hydromechanical properties which in return, constitute a potential risk for the performance of the geologic and/or engineered structures in the context of waste underground storage. Ultrasonic experiments have been implemented to characterize the EDZ extension around drifts and its evolution in time according to the structural support type (soft or rigid) and the environmental conditions. Those studies consist of two experimental components: (1) the prior auscultation of the floor and sidewalls of the gallery by ultrasonic transmission tomography, (2) the monitoring of the time-dependant evolution of EDZ and the analysis of measurable changes in the propagation of ultrasonic waves in the medium term. A code for computing these continuous in situ velocity measurements into the elastic has been developed. Then, the five dynamic elastic constants for the assumed transverse isotropic character of the rock are derived as a function of time and the distance from the drift wall. Performed a few months after the excavation of the galleries, the tomography shows that ultrasonic velocities are higher in the orthoradial direction (both in the concrete support and rock). This velocity field highlights clearly the damaged zone and induced stress shift.

Brief Comments on “Unloading Rock Mechanics” and Engineering Applications

Since rock masses are not a true continuous, homogeneous, isotropic and linear-elastic (CHILE) continuum, the loading and unloading behaviors differ greatly from each other. Professor Ha Qiulin and his co-workers have demonstrated that strength and deformational characteristics, initial rock stresses, scale effects, creep, deformation and fracture patterns are quite different and stress path dependence is particularly emphasized. As engineering unloading of the rock mass is essentially of a dynamic nature by excavation, we will first discuss the excavation process and related stabilization techniques. For the complex stress and deformation conditions around the excavated boundaries, it seems rational to define an excavation disturbed zone (EDZ) as in the last decades. In tunnel excavation, temperature and ventilation effects should be also taken into account. Space-and-time dependence on tunnel behaviors is important. Finally, further research topics are discussed.

Characterization of redox conditions in the excavation disturbed zone of a drift in the Kamaishi Mine, Japan

The excavation of drifts during construction of a geologic repository for high-level nuclear waste (HLW) could affect mechanical and hydraulic properties of the rock within a zone extending a short distance into the rock from drift walls. Related impacts on groundwater chemistry within such an Excavation Disturbed Zone (EDZ) are largely unknown, but the oxygen in air circulating through drifts could conceivably diffuse into groundwater within the EDZ and cause these solutions to become strongly oxidizing. A study was therefore undertaken of redox conditions within the EDZ of crystalline host rocks in the abandoned Kamaishi Fe–Cu mine in Japan, which is believed to be generally representative of conditions that could exist in the EDZ of a HLW repository. The chemical compositions of groundwaters flowing into three boreholes that were drilled various distances into the Kurihashi granodiorite were monitored continuously. The results indicated that dissolved oxygen concentrations tend to decrease with increasing distance into the rock. Oxygen penetrated, at most, a few meters into the rock from a drift (E.L. 250m drift) that intersected a specific fracture (Fracture No. 99), for example. A conceptual model was developed that takes into account both the reaction rate of dissolved oxygen with ferrous minerals and the diffusion rate of oxygen into the rock matrix. A quantitative evaluation of the model using a numerical solver indicated that the oxygen diffusion depth could vary from 3 to 30cm from the unsaturated/saturated zone boundary, depending on the reactive surface areas of ferrous minerals. These estimates may overestimate the migration distance of a redox front, however, because ferrous minerals other than biotite were not considered in the model and the partial pressure of O2(g) was fixed at the atmospheric value of 0.21bar throughout the unsaturated zone. More accurate assessments of redox-front behavior may be possible given better constraints on mineralogy and associated kinetic parameters (i.e., reactive surface areas and rate constants), and on microbial effects on oxygen consumption. Additionally, the use of more realistic boundary conditions on dissolved oxygen concentrations in the unsaturated zone would help reduce uncertainties in model results.

Estimation of Excavation Disturbed Zone of High Slope in the Left Bank of Jinping-I Hydropower Station

The proposed Jinping-I hydropower station is located on the middle reach of the Yalongjiang River, Sichuan Province, P.R. China. It consists of a double-curvature arch dam with a maximum height of 305 m, which will be the highest in the world. Excavation disturbed zone (EDZ) in the left bank slope is one of the most important aspects in slope stability and deformation evaluation. This paper is focused on estimation of EDZ in the left bank slope of Jinping-I hydropower station based on numerical simulation. Geological conditions of the left bank slope are firstly analyzed. Then, displacement field of the slope during excavation is calculated by finite element method (FEM). It can be indicated that the model and parameters in this paper is reasonable by comparing observed results with calculated ones. EDZ in the left bank slope can be estimated based on the calculated displacement field. It can be inferred that the range of EDZ is related to the controlling discontinuities such as fault f42-9 and Lamprophyre X etc. which are adjacent to the excavation line.

Application of a transversely isotropic brittle rock mass model in roof support design

Accurate modelling of the potential failure modes in the rock mass is an essential task towards a robust design of roof support systems in coal mines. The use of generalised rock mass properties based on averaged properties (e.g. Hoek–Brown model) has been found to limit the capability to reproduce the actual rock mass behaviour which may include a wide range of interacting and complex failure mechanisms such as shear and tension fracturing of the intact rock and shear and separation of pre-existing discontinuities, including re-activation. Recent studies have also shown that traditional models, such as the Mohr–Coulomb, may not accurately describe the behaviour of the intact rock, particularly for stress induced failures where spalling and slabbing are observed. This is mainly due to the cohesion and friction components of the shear strength of the intact rock not being mobilised at the same rate with strain-softening of the former component playing an essential role in the post peak behaviour. In addition, coal measure rocks are often transversely isotropic, both by way of the preferred orientation of clay particles within the finer grained lithology and by bedding textures and bedding partings, and this is often ignored in computer simulations. A newly developed transversely isotropic brittle rock mass model is applied in the simulation of a hypothetical and simple roadway development. A Cohesion Weakening-Friction Strengthening (CWFS) approach is adopted to describe the intact rock where the mobilisation and strain-softening of the two shear strength components are linked to plastic deformation. The impacts of anisotropy and brittle rock on the development of the excavation disturbed zone or height of softening, as often referred to, are investigated and their implication in the roof support design discussed.

Mechanical properties of abandoned and closed roadways in the Kushiro Coal Mine, Japan

The objective of this research is to clarify the mechanical properties and self-healing ability of the Excavation Damaged Zone (EDZ) around rock caverns in clastic-rock. Observations of nearly one hundred closed roadways up to fifty years old, which can be regarded as very severe EDZs with no initial sealability and are up to 300 m deep in clastic-rock, were made at the Kushiro Coal Mine, Japan, to accomplish the objective. Most old roadways were closed, though a few remain open. Closure of old roadways was mainly due to roof deflection and/or floor heave. Large plastic deformations dominated; however, severe fractures were seldom observed in closed old roadways. Rayleigh wave velocity and hydraulic conductivity in the closed old roadways were in the range of 0.3–1.2 km/s and 5×10 −7–1×10 −7 m/s, respectively, and those in EDZ and EdZ (Excavation disturbed Zone) around recently excavated roadways were 1.1–1.8 km/s and 1×10 −8–5×10 −8 m/s, respectively. The extent of EDZ around the present tailgate was in the range of 1–5 m. Mechanical excavation and prevention from water are suggested as the key points for long-term maintenance of rock repositories. Pressurization from inside the cavern to decrease the permeability of EDZ is proposed for maintenance of rock repositories in medium-hard clastic-rock masses at similar depths for long periods.

Modeling Approaches for Investigating Gas Migration from a Deep Low/Intermediate Level Waste Repository (Switzerland)

In low/intermediate-level waste (L/ILW) repositories, anaerobic corrosion of metals and degradation of organic materials produce mainly hydrogen, methane, and carbon dioxide. The Swiss reference concept for the L/ILW repository consists of parallel caverns sealed off from a single access tunnel in a deep low-permeability claystone formation. The potential buildup of excess gas pressures in the backfilled emplacement caverns was investigated in a series of two-phase flow models. In the first step, a large-scale model was constructed, implementing the 3D radial tunnel and cavern geometry with a simplified rectangular geometry. In the second step, the potential impact of the detailed geometry of the engineered barrier system (EBS) and the associated heterogeneity inside the cavern was examined using detailed models of the repository caverns, tunnel seals, access tunnel, and surrounding host rock. The simulation results from the large-scale 3D repository model show that during the early post-closure period simulated pressures can vary significantly between different parts of the repository. The simulated pressure increase in the emplacement caverns remained below the fracture pressure of the rock for realistic assumptions. Gas flow is largely limited to the EBS and the excavation disturbed zone (EDZ); thus, gas flows through and around the repository seal into the adjacent tunnel system, which is also demonstrated in the detailed repository-cavern model. The repository seal model described the detailed two-phase flow pattern of early time resaturation of the repository by water inflow from the ramp and subsequent counter flow associated with the gas flow from the repository cavern. Overall, the results of the detailed models complement and confirmed the results of the large-scale 3D model in terms of the timing of the pressure peaks and the migration of gas from the cavern into the surrounding host rock and through the repository seal.

Hydrogen solubility in pore water of partially saturated argillites: Application to Callovo-Oxfordian clayrock in the context of a nuclear waste geological disposal

In nuclear waste geological disposals, large amounts of hydrogen (H 2) are expected to be produced by different (bio-)geochemical processes. Depending on the pressure generated by such a process, H 2 could be produced as a gas phase and displace the neighbouring pore water. As a consequence, a water-unsaturated zone could be created around the waste and possibly affect the physical and physic-chemical properties of the disposal and the excavation disturbed zone around it. The present study is the first part of an ongoing research program aimed at evaluating the possible chemical evolution of the pore water–minerals–gas system in such a context. The goal of this study was to evaluate, in terms of thermodynamic equilibrium conditions, the geochemical disturbance of the pore water due to variations in hydrogen pressure, temperature and relative humidity. No heterogeneous reactions involving mineral phases of the clayrock or reactive surface sites were taken into account in the thermodynamic analysis. In the case sulphate reduction reaction is allowed, geochemical modelling results indicate that the main disturbance is the increase in pH (from around 7 up to more than 10) and an important decrease in the redox potential (Eh) related to hydrogen dissolution. This occurs from relatively low H 2 partial pressures (∼1 bar and above). Then, temperature and relative humidity (expressed in terms of capillary pressure) further displace the thermodynamic equilibrium conditions, namely the pH and the aqueous speciation as well as saturation indices of mineral phases. Finally, the results suggest that the generation of hydrogen, combined with an increase in temperature (between 30 °C and 80 °C) and a decrease in relative humidity (from 100% to 30%), should increase the chemical reactivity of the pore water–rock–gas system.

Top coal flows in an excavation disturbed zone of high section top coal caving of an extremely steep and thick seam

Compared with gentle dip long-wall caving, the length of a working face in fully-mechanized top-coal caving for extremely steep and thick seams is short, while its horizontal section is high with increasing production. But the caving ratio is low, which might result in some disasters, such as roof falls, induced by local and large area collapse of the top coal in a working face and dangers induced by gas accumulation. After the development of cracks and weakening of the coal body, the tall, broken section of the top coal (a granular medium) of an extremely steep seam (over 60°) shows clear characteristics of nonlinear movement. We have thoroughly analyzed the geological environment and mining conditions of an excavation disturbed zone. Based on the results from a physical experiment of large-scale 3D modeling and coupling simulation of top coal–water–gas, we conclude that the weakened top coal can be regarded as a non-continuous medium. We used a particle flow code program to compare and analyze migration processes and the movements of a 30 m high section top coal over time before and after weakening of an extremely steep seam in the Weihuliang coal mine. The results of our simulation, experiment and monitoring show that pre-injection of water and pre-splitting blasting improve caving ability and symmetrical caving, relieve space for large area dynamic collapse of top coal, prolong migration time of noxious gases and release them from the mined out area and so achieve safety in mining.

Analysis of the parameter identifiability of the in situ diffusion and retention (DR) experiments

In situ diffusion experiments are performed at underground research laboratories to overcome the limitations of laboratory diffusion experiments. The diffusion and retention (DR) experiments are long-term, natural-scale, in situ experiments performed in the anisotropic Opalinus Clay Formation at Mont Terri, Switzerland. Dilution data are monitored at the injection interval and overcoring data will be measured at samples around the injection interval at the end of the experiment during overcoring. Interpretation of DR experiments is complicated by the non-ideal effects caused by the sintered filter, the gap between the filter and the borehole wall and the excavation disturbed zone (EdZ). Their impact on parameter estimates has been evaluated with numerical sensitivity analyses and synthetic experiments having the same geometry and parameters as the real DR experiments. Dimensionless sensitivities of tracer concentrations in the injection interval and along the overcoring profiles have been computed numerically. They have been used to identify the tracer parameters that can be estimated with the least uncertainty from tracer dilution and overcoring data. Sensitivities of tracer dilution data change with time and those of overcoring concentrations along the bedding are different from those along profiles normal to the bedding. Concentrations along overcoring profiles are sensitive to the effective diffusion normal to the bedding. Synthetic experiments generated with prescribed known parameters have been interpreted automatically with INVERSE-CORE 2D and used to evaluate the relevance of non-ideal effects and determine parameter identifiability in the presence of random errors for HTO and 22Na +. Model results show that it is difficult to estimate the parameters of the undisturbed clay when the tracer dilution data contain noise. The convergence of the estimation algorithm improves when the starting values are smaller than the true parameters. Although the parameters of the undisturbed clay and the EdZ cannot be estimated using tracer dilution data, their joint estimation from overcoring noisy data is possible for standard deviations of the noise up to 0.05. Large estimation errors in the parameters of the undisturbed clay and poor fits are obtained when the assumption about the existence of EdZ is incorrect. The effective diffusion of the filter is a key parameter for the interpretation of the experiments. Small errors in the volume of the circulation system do not affect the estimates of the component of the effective diffusion of undisturbed clay parallel to bedding. The results of the identifiability analysis clearly shows that: (1) The proper interpretation of in situ DR experiments requires accounting for the filter and the EdZ and (2) Overcoring data allow a more accurate estimation of the parameters of the undisturbed clay than the tracer dilution data.

Seismic Tomography Investigation in 140m Gallery in the Horonobe URL Project

AbstractThe Japan Atomic Energy Agency (JAEA) established the Horonobe Underground Research Laboratory (URL) Project at Horonobe, in Hokkaido, Japan to enhance reliability of nuclear waste disposal technologies to be developed in deep sedimentary environments. JAEA has undertaken a number of in-situ experiments to determine changes in the properties of the host rock and the extent of the excavation disturbed zone (EDZ) created by the excavation of underground galleries for the disposal of radioactive waste. This paper reports a seismic tomography survey (using a hammer seismic source) of the “140m Gallery” at a depth of 140m below the surface of the Horonobe URL. The observation area was 3m square on the horizontal plane along the sidewall of the 140m Gallery. The measurement was repeated with the progress of excavation of a tunnel. In this experiment, the distribution of seismic velocity in the rock around the new tunnel and its decrease as the tunnel was dug, were observed using a simple small-scale seismic tomography system. The data collected show that this system can be used to capture the EDZ around tunnels.

Numerical model of a long-term in situ diffusion and retention (DR) experiment in Opalinus Clay

Determining diffusion parameters under real conditions is necessary for the performance assessment of a deep geological repository. Here we present a numerical model for the interpretation of a long-term in situ diffusion and retention (DR) experiment performed on Opalinus clay (OPA) at Mont Terri underground rock laboratory in Switzerland using a comprehensive set of tracers which includes neutral (HTO, HDO), anionic (Cl, Br, I), weakly-sorbing (22Na, 133Ba and 85Sr) and strongly-sorbing tracers (60Co, 137Cs). Compared to the model used for scoping calculations, our current model accounts for the presence of a sintered filter, a gap between the filter and borehole wall and an excavation disturbed zone (EdZ). Sensitivity analyses have been performed to identify the relevance of these non-ideal effects and evaluate identifiability of diffusion anisotropy and distribution coefficients. Results of sensitivity analyses indicate that tracer concentrations are not sensitive to De of gap, but very sensitive to De of filter except for HTO and HDO. Concentrations of HTO, HDO, I, Na, Sr and Ba are sensitive to De of EdZ while those of strongly-sorbing tracers such as Co and Cs are much less sensitive. All sorbing tracers are sensitive to changes in Kd of clay. The relevance of diffusion anisotropy increases with time for all tracers except strongly-sorbing tracers.

Comprehensive assessment on dynamic roof instability under fractured rock mass conditions in the excavation disturbed zone

The damage process of fractured rock mass showed that the fracture in rocks induced roof collapse in Yangchangwan Coal Mine, China. The rock mass was particularly weak and fractured. There occurred 6 large-scale dynamical roof falls in the excavation disturbed zone (EDZ) with the collapsing volume of 216 m 3. First, the field detailed geological environment, regional seismic dynamics, and dynamic instability of roadways were generally investigated. Second, the field multiple-index monitoring measurements for detecting the deep delamination of the roof, convergence deformation, bolt-cable load, acoustic emission (AE) characteristic parameters, total AE events, AE energy-releasing rate, rock mass fracture, and damage were arranged. Finally, according to the time-space-strength relations, a quantitative assessment of the influence of rock-mass damage on the dynamic roof instability was accomplished.

Impact of Silicon Migration Through Buffer Material on the Lifetime of Vitrified Waste

AbstractA sensitivity analysis was conducted to evaluate the impact of silicon migration through buffer material on the lifetime of vitrified waste. The results indicate that the lifetime depends on a combination of the dissolved glass fraction in the non-steady-state phase controlled by the silicon pore diffusion coefficient (Dp) and the silicon distribution coefficient (Kd) in the buffer material and the steady-state dissolution rate defined by Dp and the groundwater flow rate (Q) in the excavation disturbed zone. In the case where the glass dissolution rate reaches the steady-state dissolution rate, the sensitivity of the lifetime to Dp and Q varies according to the magnitude relationship between Dp and Q. We also discuss the impact on the lifetime of glass hydration, which proceeds simultaneously with glass matrix dissolution. The results show that glass hydration is less important for the lifetime than glass matrix dissolution in an open system and it can be concluded that silicon migration through the buffer material will be an important process for estimating the lifetime of the vitrified waste. A preliminary calculation of the long-term waste behavior with realistic assumptions indicates the importance of the silicon migration parameters Kd and Dp, which control the dissolution behavior of the vitrified waste in the non-steady-state phase, for evaluating radionuclide release.

A multiple-code simulation study of the long-term EDZ evolution of geological nuclear waste repositories

This simulation study shows how widely different model approaches can be adapted to model the evolution of the excavation disturbed zone (EDZ) around a heated nuclear waste emplacement drift in fractured rock. The study includes modeling of coupled thermal-hydrological-mechanical (THM) processes, with simplified consideration of chemical coupling in terms of time-dependent strength degradation or subcritical crack growth. The different model approaches applied in this study include boundary element, finite element, finite difference, particle mechanics, and elasto-plastic cellular automata methods. The simulation results indicate that thermally induced differential stresses near the top of the emplacement drift may cause progressive failure and permeability changes during the first 100 years (i.e., after emplacement and drift closure). Moreover, the results indicate that time-dependent mechanical changes may play only a small role during the first 100 years of increasing temperature and thermal stress, whereas such time-dependency is insignificant after peak temperature, because of decreasing thermal stress.

Modeling of damage, permeability changes and pressure responses during excavation of the TSX tunnel in granitic rock at URL, Canada

This paper presents numerical modeling of excavation-induced damage, permeability changes, and fluid-pressure responses during excavation of a test tunnel associated with the tunnel sealing experiment (TSX) at the Underground Research Laboratory (URL) in Canada. Four different numerical models were applied using a wide range of approaches to model damage and permeability changes in the excavation disturbed zone (EDZ) around the tunnel. Using in situ calibration of model parameters, the modeling could reproduce observed spatial distribution of damage and permeability changes around the tunnel as a combination of disturbance induced by stress redistribution around the tunnel and by the drill-and-blast operation. The modeling showed that stress-induced permeability increase above the tunnel is a result of micro and macrofracturing under high deviatoric (shear) stress, whereas permeability increase alongside the tunnel is a result of opening of existing microfractures under decreased mean stress. The remaining observed fracturing and permeability changes around the periphery of the tunnel were attributed to damage from the drill-and-blast operation. Moreover, a reasonably good agreement was achieved between simulated and observed excavation-induced pressure responses around the TSX tunnel for 1 year following its excavation. The simulations showed that these pressure responses are caused by poroelastic effects as a result of increasing or decreasing mean stress, with corresponding contraction or expansion of the pore volume. The simulation results for pressure evolution were consistent with previous studies, indicating that the observed pressure responses could be captured in a Biot model using a relatively low Biot-Willis’ coefficient, α ≈ 0.2, a porosity of n ≈ 0.007, and a relatively low permeability of k ≈ 2 × 10−22 m2, which is consistent with the very tight, unfractured granite at the site.

Study of the initiation and propagation of excavation damaged zones around openings in argillaceous rock

The study of the creation and evolution of the excavation disturbed zone (EDZ) in argillaceous rocks is a major issue for the safety of nuclear wastes underground repositories. In this context, the argillaceous Tournemire site has provided a unique opportunity to study the evolution of the EDZ with time thanks to the existence of three openings of different ages. A thorough characterization of the EDZ has been conducted by different means such as visual observation, analysis of samples extracted from drilled boreholes, EDZ permeability measurements, etc. On the basis of these measurements, a conceptual model of the EDZ initiation and propagation at the Tournemire site has been proposed. In order to validate this model, numerical simulations of increasing complexity have been carried out. In a first attempt, the response of the rock mass to the excavation phase, followed by seasonal cyclic variations of temperature and relative humidity inside the opening, has been simulated by means of a purely mechanical analysis, using a simple elastic material model. The EDZ has been estimated by post-processing the calculated stress states, using a Mohr–Coulomb failure criterion. The results obtained show that no EDZ could be predicted unless adopting a low cohesion value for the rock mass. Moreover, the deferred nature of the EDZ formation in Tournemire could not be reproduced. These limitations have then been suppressed by using a coupled viscoplastic-damaging mechanical model, the parameters of which have been identified from different laboratory experiments. With this model, a time evolution of the EDZ could be predicted, but the EDZ pattern could not match the one observed in situ. Finally, in view of the importance of the hydraulic couplings, unsaturated hydro-mechanical calculations have been carried out to investigate the effect of the numerous seasonal variations cycles and the resulting shrinkage.