FEBEX Stage2: UPC modelling report 2020

The present report contains the description of a model for the large-scale in situ heating test FEBEX (full-scale engineered barrier experiment). In this test, after five years of heating, one of the heaters was switched off and the experiment was partially dismantled, allowing the final state of the barrier to be observed directly. In this way, very valuable information on the state of the bentonite at the end of the test was obtained. The test has received attention during the initial (Gens et al., 1998) and intermediate stages (Alonso & Alcoverro, 2005). Moreover, Gens et al. (2009) discussed the thermal, hydraulic and mechanical observations in the bentonite barrier and in the host rock, paying special attention to the progress of hydration in the barrier, the effects of heating and vapour transport, and the development of swelling pressures in the barrier.Preprin

Análisis de riesgos en proyectos de almacenamiento geológico de CO2

One of the causes of climate change is the anthropogenic emission of greenhouse gases, mainly CO2. To reduce these emissions one of the options that exist is the geological storage of CO2. This thesis sets out the criteria for selecting suitable sites for the geological storage of CO2, as well as its associated costs and risks, and finally, an analysis of these risks, for which specific methodologies for analyzing risks for geological CO2 storage projects.Una de las causas del cambio climático es la emisión antropogénica de gases de efecto invernadero, principalmente el CO2. Para reducir estas emisiones una de las opciones que existen es el almacenamiento geológico de CO2. En esta tesis se exponen los criterios de selección de emplazamientos adecuados para el almacenamiento geológico de CO2, así como sus costes y riesgos asociados para, por último, proceder a un análisis de estos riesgos, para lo cual se han elaborado metodologías específicas de análisis de riesgos para proyectos de almacenamiento geológico de CO2

Influence of time-dependence on failure of echelon rock joints through a novel DEM model

This is an Accepted Manuscript of an article published by Taylor & Francis Group in [European Journal of Environmental and Civil Engineering] on [September 2015], available online at: http://www.tandfonline.com/10.1080/19648189.2015.1064624This article investigates the time-dependent influence on the shear failure behaviour of parallel rock joints in the echelon arrangement due to chemical weathering, which can be treated as a generalised time-dependency of the rock material. A time-dependent parameter alpha, identifying the accumulated relative mass removal of bonding material, has been implemented into a novel distinct element method bond contact model. This model is based on a series of mechanical test on bonded aluminium rods with different bond geometries. The numerical direct shear test results of echelon rock joints characterised by different values of alpha show that increasing time-dependent parameter alpha can lead to a lower crack initiation and peak stresses. This is accompanied by a growing ratio of the microscopic compressive-shear-torsional (CST) bond failure number of bond failures to the total number of failures, except for the case without weathering influence. High values of alpha render the material bridge a weaker part to be cut through, generating a large number of CST bond breakages along the central shear axis.Peer ReviewedPostprint (author's final draft

DEM simulation of soil-tool interaction under extraterrestrial environmental effects

In contrast to terrestrial environment, the harsh lunar environment conditions include lower gravity acceleration, ultra-high vacuum and high (low) temperature in the daytime (night-time). This paper focuses on the effects of those mentioned features on soil cutting tests, a simplified excavation test, to reduce the risk of lunar excavation missions. Soil behavior and blade performance were analyzed under different environmental conditions. The results show that: (1) the cutting resistance and the energy consumption increase linearly with the gravity. The bending moment has a bigger increasing rate in low gravity fields due to a decreasing moment arm; (2) the cutting resistance, energy consumption and bending moment increase significantly because of the raised soil strength on the lunar environment, especially in low gravity fields. Under the lunar environment, the proportions of cutting resistance, bending moment and energy consumption due to the effect of the van der Waals forces are significant. Thus, they should be taken into consideration when planning excavations on the Moon. Therefore, considering that the maximum frictional force between the excavator and the lunar surface is proportional to the gravity acceleration, the same excavator that works efficiently on the Earth may not be able to work properly on the Moon.Peer ReviewedPostprint (author's final draft

Increasing understanding and confidence in THM simulations of engineered barrier systems

Previous studies on the modelling of coupled thermo-hydro-mechanical (THM) processes in bentonite-based engineered barrier systems (EBSs) showed the sensitivity of the output quantities to changes in the input parameters. To investigate the effects of uncertainties on the modelling results, to improve the understanding of the coupled processes active in the repository near field and to gain in-depth understanding of model uncertainties of different codes, a sensitivity analysis and code comparison of EBS simulations was performed within the Task Force on Engineered Barrier Systems. The analysis included variations in material parameter values, boundary and initial conditions, considered physical processes and model geometries, amounting to 60 different cases. This in-depth analysis helped evaluate the influence of parameter and conceptual uncertainties on the results of coupled THM simulations and to identify key parameters and processes. The cross-code comparison encouraged a fruitful exchange among modelling teams and led to very good agreements between the results of the different codes. Serving as a benchmark example for THM-coupled simulations of bentonite-based EBSs, the study helped increase the confidence in the modelling capabilities of several codes used for safety evaluations of repositories for spent fuel and high-level radioactive waste.Peer ReviewedPostprint (author's final draft

A new approach to model geomaterials with heterogeneous properties in thermo-hydro-mechanical coupled problems

The main objective of this article is to present a new approach to model coupled thermo-hydro-mechanical problems considering geomaterials with heterogeneous properties. This approach has been implemented in the software CODE_BRIGHT and it provides the possibility of considering geomaterials with a spatially correlated heterogeneous field of porosity, following a normal distribution. This spatial correlation can be isotropic or anisotropic. An important feature of this approach is that material properties such as intrinsic permeability, thermal conductivity, diffusivity, retention curve, elastic modulus or cohesion are defined as a function of porosity and, thus, they become heterogeneous with spatial correlation and, eventually, anisotropic. A validation exercise and other basic numerical examples have been carried out to illustrate the possibilities of the proposed approach. The results, which have been compared with a homogeneous case, show that considering heterogeneous fields can be relevant in different modelling problems, especially coupled thermo-hydro-mechanical problems.This research was supported by the CODE_BRIGHT Project (CIMNE, International Centre for Numerical Methods in Engineering) and by the DECOVALEX Project. The second author was supported by a CSC scholarship (No. 202008390058). The CODE_BRIGHT project is funded by a Consortium composed by SKB (Sweden), Posiva (Finland), GRS (Germany) and ANDRA (France). DECOVALEX is an international research project comprising participants from industry, government and academia, focusing on development of understanding, models and codes in complex coupled problems in sub-surface geological and engineering applications; DECOVALEX-2023 is the current phase of the project. The authors appreciate and thank the DECOVALEX-2023 Funding Organisations ANDRA, BASE, BGE, BGR, CAS, CNSC, COVRA, US DOE, ENRESA, ENSI, JAEA, KAERI, NWMO, NWS, SÚRAO, SSM and Taipower for their financial and technical support of the work described in this paper. The statements made in the paper are, however, solely those of the authors and do not necessarily reflect those of the Funding Organisations. Special thanks to I.P. Damians for facilitating the original numerical model used in his work (Damians et al., 2020), in which one of the models presented in this article has been based.Peer ReviewedPostprint (published version

Modelling underground excavations in rock masses with anisotropic time-dependent behaviour

When modelling rock masses that behave anisotropically and in addition present a time dependent behaviour, it is relevant to select a constitutive model able to represent their actual behaviour realistically. This article presents an alternative anisotropic time-dependent constitutive model able to predict the coupling between anisotropic behaviour and time-dependent (or viscous) behaviour. The viscous behaviour is simulated with the Burgers model and all elastic springs and viscous dashpots are considered to exhibit transversely isotropic properties. The proposed constitutive model has been implemented in the finite element method software CODE_BRIGHT. To verify the basic anisotropic elastic solution, it has been compared with that of PLAXIS results. And to verify the isotropic viscoelastic solution, it has been compared with analytical solutions. Furthermore, the proposed constitutive model has been used to predict the behaviour of samples from laboratory tests. Finally, parametric analyses have been carried out to investigate the influence of different factors on tunnelling responses, including the selection of different constitutive models, anisotropy of initial stresses and anisotropy of material properties. The proposed model provides an alternative method for the preliminary design of geotechnical engineering works involving geomaterials that exhibit anisotropic time-dependent behaviour.Peer ReviewedPostprint (published version

Numerical analysis of anisotropic stiffness and strength for geomaterials

In numerical modelling, selection of the constitutive model is a critical factor in predicting the actual response of a geomaterial. The use of oversimplified or inadequate models may not be sufficient to reproduce the actual geomaterial behaviour. That selection is especially relevant in the case of anisotropic rocks, and particularly for shales and slates, whose behaviour may be affected, e.g. well stability in geothermal or oil and gas production operations. In this paper, an alternative anisotropic constitutive model has been implemented in the finite element method software CODE_BRIGHT, which is able to account for the anisotropy of shales and slates in terms of both deformability and strength. For this purpose, a transversely isotropic version of the generalised Hooke's law is adopted to represent the stiffness anisotropy, while a nonuniform scaling of the stress tensor is introduced in the plastic model to represent the strength anisotropy. Furthermore, a detailed approach has been proposed to determine the model parameters based on the stress–strain results of laboratory tests. Moreover, numerical analyses are performed to model uniaxial and triaxial tests on Vaca Muerta shale, Bossier shale and slate from the northwest of Spain (NW Spain slate). The experimental data have been recovered from the literature in the case of the shale and, in the case of the slate, performed by the authors in terms of stress-strain curves and strengths. A good agreement can be generally observed between numerical and experimental results, hence showing the potential applicability of the approach to actual case studies. Therefore, the presented constitutive model may be a promising approach for analysing the anisotropic behaviour of rocks and its impact on well stability or other relevant geomechanical problems in anisotropic rocks.The experimental part of the slate in this work was funded by REPSOL S.A. The numerical part of this work was supported by the CODE_BRIGHT Project (International Centre for Numerical Methods in Engineering). The work of the second and fourth authors was possible thanks to the Spanish Ministry of Science and Innovation, who funded the project, awarded under Contract Reference No. RTI 2018-093563-B-I00, partially financed by means of the European regional development fund (ERDF) funds from the European Union (EU).Peer ReviewedPostprint (published version

A case of compatibility between quarrying of ornamental granite and forest exploitation

A particular development is proposed to mine some good quality out crops of granite found in a forest exploitation of eucalypts. The exploitation has been designed with a quarrying method, in which small open cast pits are opened and quarried sequentially, and later filled with the waste of the new open pit. Soil is finally used to cover this waste, so new growing tree areas are gaine

Study on multi-period palaeotectonic stress fields simulation and fractures distribution prediction in Lannigou gold mine, Guizhou

A significant controlling factor for gold mineralisation is the tectonic stress field, and the fractures formed under its action are the migration channels and ore-holding spaces of ore-forming fluids, which often directly control the migration and accumulation of ore-forming fluids. Therefore, performing quantitative prediction research on the distribution of fractures in the Guizhou, Lannigou gold deposit in order to identify potential fluid flow pathways is of utmost importance for ore prospecting in practical. In this study, a 3D geological entity model was generated based on the GOCAD platform by analysing and processing the geological data of the studied area, as well achieved is the accurate characterisation of the study area’s geometric model. By integrating regional tectonic evolution history analysis, geological interpretation, rock mechanics experiments and acoustic emission testing, the finite element method was utilised to create a 3D geomechanical model of the research area, the paleotectonic stress field after the Indosinian and Yanshanian movements were superimposed was simulated, in associated with the rock failure criterion, the comprehensive fracture rate parameter (Iz) is introduced to predict the fracture distribution. The results show that the research area’s maximum principal stress is primarily distributed between 153.85 and 189.53 MPa, and the maximum shear stress is between 83.53 and 98.42 MPa. The spatial distribution of faults influences the stress distribution characteristics significantly, and the stress level is relatively high at the intersection of the fault, the end of the fault and the vicinity of the fault zone, and the stress value between the faults is relatively low. The tectonic stress field primarily controls the distribution and development of fractures, which is usually consistent with the areas with high values of maximum principal stress and maximum shear stress. Using the combined modeling technique of GOCAD and midas GTS to realize the conversion from 3D geological model to geomechanical model, a set of comprehensive fracture distribution prediction technique for the superposition of multi-stage tectonic stress fields of mineral deposits in complex tectonic areas has been formed, and provide a reference for the prediction of fracture distribution in similar complex structural areas.This study was supported by the program of China Scholarships Council (No. 202006670005); the National Natural Science Foundation of China (Project Nos. 51964007, 52264004, 52104080, 41962008); the Guizhou Province Science and Technology Support Program Project (Number: QIANKEHE Support [2021] General 516); Scientific and Technological Innovation Talents Team in Guizhou Province (Project No. [2019]5619); the Guizhou Province Highlevel Innovative Talents Training Project (Grant No. JZ2016-4011). Major Collaborative Innovation Project for Strategic Action of Mineral Search Breakthrough in Guizhou Province ([2022] ZD005); Natural Science Special (Special Post) Scientific Research Fund Project of Guizhou University (Project No. Guizhou University Special Post (2021) 51).Peer ReviewedPostprint (published version