Hydromechanical response of a bedded argillaceous rock formation to excavation and water injection

2015 ◽  
Vol 52 (1) ◽  
pp. 1-17 ◽  
Author(s):  
A.D. Le ◽  
T.S. Nguyen
Keyword(s):  
Rock Mass ◽  
Pore Pressure ◽  
Damage Zone ◽  
Water Injection ◽  
Constitutive Relationship ◽  
Opalinus Clay ◽  
Anisotropic Plastic ◽  
Mont Terri ◽  
Excavation Damage

Opalinus clay is a candidate host formation for the geological disposal of nuclear wastes in Switzerland. The understanding of its long-term mechanical (M) and hydraulic (H) behaviour is an essential requirement for the assessment of its performance as a barrier against radionuclide transport. To study the HM response of Opalinus clay, a microtunnel, 13 m in length and 1 m in diameter, was excavated in that formation at the Mont Terri Underground Research Facility. The rock mass was equipped with sensors to measure the deformation and pore pressure in the rock mass during and after the excavation. A mathematical model that couples the equations of flow and mechanical equilibrium was developed to simulate the HM response of the rock mass. An anisotropic plastic constitutive relationship, based on a microstructure tensor approach, was incorporated in the model. Creep was also considered, as well as the anisotropy of permeability. It is shown that the model satisfactorily predicts the shape and extent of the excavation damage zone (EDZ), deformation, and pore pressure in the rock mass. It is also shown that anisotropy and creep play an important role in the HM response of the rock mass to excavation. The model was further used to simulate water injection tests performed at the test section in the microtunnel. The results show that EDZ, due to its high permeability, is a preferential groundwater flow path along the microtunnel.

scholarly journals Comparison between in situ and laboratory diffusion studies of HTO and halides in Opalinus Clay from the Mont Terri

2004 ◽  
Vol 92 (9-11) ◽  
Author(s):  
Etienne Tevissen ◽  
J. M. Soler ◽  
P. Montarnal ◽  
A. Gautschi ◽  
Luc R. Van Loon
Keyword(s):  
Tritiated Water ◽  
Opalinus Clay ◽  
Diffusion Experiment ◽  
Diffusion Technique ◽  
Diffusion Studies ◽  
Through Diffusion ◽  
Mont Terri

SummaryA long-term single-borehole diffusion experiment (DI) using tritiated water (HTO) and stable iodide (All HTO results obtained with a through diffusion technique are within the same range as those obtained in the

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>

3D Predictive HM-modeling in the heterogeneous Opalinus Clay of the Mont Terri rock laboratory and validation with monitoring data from a mine-by test

2021 ◽  
Author(s):  
Chao Li ◽  
David Jaeggi ◽  
Christophe Nussbaum ◽  
Paul Bossart
Keyword(s):  
Pore Pressure ◽  
Initial Conditions ◽  
Near Field ◽  
Early Time ◽  
Monitoring Data ◽  
Opalinus Clay ◽  
Stress Monitoring ◽  
Rock Laboratory ◽  
Mont Terri ◽  
Mont Terri Rock Laboratory

<p>The Mont Terri rock laboratory began in 1996 with 8 niches, followed by a research tunnel in 1998. Since then the laboratory has been expanded every 10 years, mainly in the shaly facies of the Opalinus Clay. In March 2018, south of the existing laboratory, the Mont Terri Project Partners initiated another extension «Gallery 18» of the Mont Terri rock laboratory mainly located in sandy facies of the Opalinus Clay. In October 2019 the extension was finished, resulting in more than 500 m of additional galleries and niches for new experiments. In the frame of this extension, for the first time a heterogeneous mine-by test, comprising a sheet of sandy facies and carbonate-rich sandy facies sandwiched between shaly facies was conducted in the rock laboratory. This so-called MB-A experiment (hydro-mechanical characterization of the sandy facies before and during excavation) consists of two lateral niches for instrumentation and monitoring and a test gallery of 30 m length oriented perpendicular to the latter. The instrumentation based on 26 boreholes with lengths up to 40 m consists of pore pressure transducers, extensometers, inclinometers and stress monitoring stations. It was finished several months before excavation of the test section was started in order to assure equilibration close to the initial conditions. Excavation of the test gallery running parallel to bedding strike was carried out in May 2019 in 20 days.</p><p>Elastic predictive modeling is performed in 3D to estimate the hydro-mechanical behavior of the rock mass during a sequential excavation according to effective daily advances and as-is sensor locations. The modeling results are compared with monitoring data. The calculation predicts a rotation of the early time near-field pore pressure reduction from perpendicular to parallel to bedding for late times. In general, monitored peak pore water pressures were higher than predicted, with a remarkable phase shift depending on distance and spatial position with respect to the drift. Monitored deformations were clearly underestimated with the elastic calculation. The overall behavior of the excavation in the sandy facies was unexpectedly not so different from former excavations in shaly facies.</p><p>A parametric study was performed to assess key parameters of potential effects of excavation on the hydromechanical responses of the excavation. It is concluded that adapted constitutive laws are needed in order to properly predict the hydromechanical response in stiffer claystone, such as for instance the sandy and carbonate-rich sandy facies of the Opalinus Clay.</p>

scholarly journals Coupled HM modeling assists in designing CO2 long-term periodic injection experiment (CO2LPIE) in Mont Terri rock laboratory 

2021 ◽  
Author(s):  
Dario Sciandra ◽  
Víctor Vilarrasa ◽  
Iman Rahimzadeh Kivi ◽  
Roman Makhnenko ◽  
Christophe Nussbaum ◽  
...  
Keyword(s):  
Lag Time ◽  
Opalinus Clay ◽  
Bedding Planes ◽  
Rock Laboratory ◽  
Hydraulic Anisotropy ◽  
The One ◽  
Mont Terri ◽  
Mont Terri Rock Laboratory ◽  
Injection Experiment

<p>We are performing a series of coupled hydro-mechanical (HM) simulations to model CO<sub>2</sub> flow through Opalinus Clay at the Mont Terri rock laboratory in the CO<sub>2</sub> Long-term Periodic Injection Experiment (CO<sub>2</sub>LPIE). CO<sub>2</sub>LPIE aims at inter-disciplinary investigations of the caprock sealing capacity in geologic CO<sub>2</sub> storage in a highly monitored environment at the underground laboratory scale. Numerical modeling allows us to gain knowledge on the dynamic processes resulting from CO<sub>2</sub> periodic injection and to assist the experimental design. The cyclic injection parameters (i.e., the period and the amplitude) have to be optimized for the field experiment and therefore different values are taken into account. Opalinus Clay is a claystone with nanoDarcy permeability that contains well developed bedding planes responsible for its anisotropic HM behavior. The hydraulic anisotropy is defined by a permeability parallel to the bedding planes being three times the one perpendicular to it. Additionally, the drained Young’s modulus is measured to be 1.7 GPa parallel and 2.1 GPa perpendicular to bedding. Excavation reports by swisstopo document a SSE-dip of 45° for the bedding planes at the experiment location. CO<sub>2</sub> injection generates a mean overpressure of 1 MPa into the brine that propagates into the formation. The differential pressure between CO<sub>2</sub> and formation water, i.e., capillary pressure, is lower than the entry pressure and thus, CO<sub>2</sub> diffuses through the pores but does not advect in free phase. The liquid overpressure distribution is distorted by the hydraulic anisotropy, preferentially advancing along the bedding planes, as the associated permeability is higher than the one perpendicular to the bedding. The pore pressure buildup induces a poromechanical stress increase and an expansion of the rock that leads to a permeability enhancement of up to two orders of magnitude. The cyclic stimulation propagates trough the domain faster and with a lag time and an attenuation, both of which increase with distance from the source with, their values being dependent on permeability, porosity and stiffness of the rock. As a result of the model orthotropy, the attenuation and the lag time change with direction, i.e. they are higher in the direction perpendicular to the bedding and lower in the direction parallel to the bedding. Given the very low permeability of Opalinus Clay, the overpressure generated requires a long time to diffuse into the rock. Furthermore, the amplitude attenuation dissipates quite rapidly, so monitoring wells should be placed as close to the injection well as possible. The study of amplitude attenuation and time lag is necessary to determine how they can be utilized to evaluate the evolution of the HM properties as the rock is altered by the acidic nature of CO<sub>2</sub>-brine mixture Comparison between field data and numerical simulations will be a useful asset to fill the gap.</p>

scholarly journals Building the bridge between safety requirements and numerical modeling: an example considering crack development of Opalinus clay in laboratory and field scales

2021 ◽  
Vol 1 ◽  
pp. 165-167
Author(s):  
Tuanny Cajuhi ◽  
Jobst Maßmann ◽  
Gesa Ziefle
Keyword(s):  
Numerical Modeling ◽  
Numerical Model ◽  
Large Scale ◽  
Numerical Models ◽  
Laboratory Scale ◽  
Opalinus Clay ◽  
Air Humidity ◽  
Mont Terri

Abstract. Salt, crystalline and clay formations are under discussion as potential host rocks for storage of heat-generating radioactive waste. Each of these rocks has a different structure and composition, and consequently a different material behavior. The latter needs to be studied and evaluated with respect to the main aim: to find a place to store the waste in a safe and sustainable manner. Several requirements in the context of the safety of a repository need to be fulfilled, concerning the long-term as well as the operational phase. One key point in this matter is the integrity, which refers to retention of the isolating rock zone's containment capabilities. With the focus on some experimental and numerical investigations on the excavation influenced near-field behavior of Opalinus clay (OPA), this contribution aims to illustrate an example for the role of numerical modeling in safety assessment. Once, e.g. anthropogenic action such as excavation starts, the natural state of equilibrium in the formation is disturbed. Trying to restore it, the rock deforms (convergence) and/or releases energy in other ways such as cracking. This could lead to loss of integrity since crack nucleation and propagation can affect the mechanical stability and create paths to transport contaminants. During operation in the excavated rock, environmental changes, e.g. temperature and humidity, further affect its behavior. The understanding of these dynamic phenomena ideally needs to occur at the in situ scale; however, performing an experiment in the spatial and time scales of interest is not always possible. For this reason, the in situ problem needs to be formulated, abstracted and mathematically modeled. The interpretation of the results must take place with simplifying assumptions and complementary laboratory scale experiments can be used to improve understanding of the system. The real problem is approached stepwise, each step associated to the size of the model and its complexity. The gradually obtained knowledge is necessary to achieve a better understanding of the process and to evaluate the capacities and limitations of the models. This contribution aims at showing the basic practical steps for numerical modeling with particular focus on the preparation and interpretation of the models and results, e.g. model calibration, verification and validation. As an example, the OPA at the Mont Terri site is chosen. The material parameters are obtained either experimentally or from the literature. We choose and perform laboratory scale simulations that are related to nearly the same mechanism as in the in situ scale. To have a first impression on the latter, a simplified, large-scale numerical model is prepared. The mechanism in study is drying and wetting, which is associated with shrinkage and swelling. We analyze the pore pressure and stress development in both scales. Thus, hydraulic mechanically coupled approaches are essential. The concept of effective stress is used, which combines the contributions of the solid and fluid phases (gas and liquid). In the current modeling approach, the gas pressure remains constant (atmospheric pressure) and during drying, the liquid pressure induces capillary pressure development and decrease of saturation. The laboratory scale simulation is important to evaluate the model of choice and to assess potential numerical problems. Furthermore, it can be used to perform a sensitivity study of material and numerical parameters. This step is necessary during the development or extension of numerical models as well as to evaluate their applicability on new research questions. The simplified in situ scale numerical model is then extended. In this phase the numerical model is evaluated once again, especially with respect to its complexity. Furthermore, specific questions related to this scale are posed: overall behavior of the rock, influence of the excavation, seasonal and long-term effects. In this contribution we deal with the long-term cyclic deformation (CD-A) experiment. The CD-A experiment has been taking place in the Mont Terri Rock Laboratory since October 2019. It consists of twin niches, a closed and an open niche, subjected to either high air humidity or seasonal humidity changes leading to saturation/desaturation during summer/winter in the OPA, respectively. Several parameters are periodically or continuously measured, including relative air humidity, convergence and crack development. We attempt to transfer the knowledge and numerical models developed in the small scale to the large scale and to evaluate the possibilities and limitations of the chosen approaches by comparing the numerical and experimental results.

Influence Research of Underground Caverns Blasting Excavation on Excavation Damage Zone of Adjacent Cavern

2013 ◽  
Vol 838-841 ◽  
pp. 901-906 ◽  
Author(s):  
Peng Cheng Xu ◽  
Qian Dong ◽  
Xin Ping Li ◽  
Yi Luo
Keyword(s):  
Numerical Simulation ◽  
Rock Mass ◽  
Kinematic Hardening ◽  
Damage Zone ◽  
Side Wall ◽  
Measured Data ◽  
Excavation Damage Zone ◽  
Underground Caverns ◽  
Blasting Excavation ◽  
Excavation Damage

The influence of the single cavern blasting excavation in underground caverns on the stability of surrounding rock of adjacent caverns can not be ignored.In–situ blasting vibration test and dynamic finite element analysis were used to study the laws of blasting seismic wave propagation, two different material constitutive models were adopted, compared with measured data,to select material constitutive model which was more in line with the dynamic characteristics of rock mass in underground caverns.On this basis, the influence mechanism for blast–induced EDZ(Excavation Damage Zone) of the adjacent cavern is studied through the method of numerical simulation. The results show that the numerical simulation resulted by adopting kinematic hardening model were more close to measured data than adopting ideal elastic–plastic model; the middle part of adjacent tunnel side wall facing blasting had the largest damaged rock mass range; both sides of the arch and the foundation rock of the adjacent cavern emerged damaged rock mass area, and the area of adjacent tunnel side wall facing blasting was larger than side wall not facing blasting.

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