Armand, Gilles

Souley, Mountaka

HAL-INERIS

A viscoplastic model including damage for deepargillaceous rocks : blind predictions of drift behaviourGilles Armand, Mountaka SouleyTo cite this version:Gilles Armand, Mountaka Souley. A viscoplastic model including damage for deep argillaceousrocks : blind predictions of drift behaviour. 2. International Conference on computationalmethods in tunnelling, Sep 2009, Bochum, Germany. <ineris-00973348>HAL Id: ineris-00973348https://hal-ineris.ccsd.cnrs.fr/ineris-00973348Submitted on 4 Apr 2014HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.L’archive ouverte pluridisciplinaire HAL, estdestine´e au de´poˆt et a` la diffusion de documentsscientifiques de niveau recherche, publie´s ou non,e´manant des e´tablissements d’enseignement et derecherche franc¸ais ou e´trangers, des laboratoirespublics ou prive´s.A viscoplastic model including damage for deep argillaceousrocks: blind predictions of drift behaviourGilles Armand1 and Mountaka Souley21ANDRA - Agence nationale de gestion des déchets radioactifs, Laboratoiresouterrain de Meuse Haute Marne, Bure, France2 INERIS- Institut national de l'environnement industriel et des risques, Nancy,FranceAbstractIn order to demonstrate the feasibility of a radioactive waste repository in clay-stoneformation, the French national radioactive waste management agency (ANDRA)started in 2000 to build an underground research laboratory at Bure. One of the keyissues is to understand long term behaviour of drifts. Souley et al. [4] proposes a newmacroscopic viscoplastic model of Callovo-Oxfordian clay-stones based on bothlaboratory and field observations which aimed to improve the viscoplastic strainpredictions around the drifts. An example of a blind prediction of the excavation of adrift parallel to ah (using this new model) is presented and compared to in situmeasurement. Results show the influence the damage state on viscoplastic strainrates, advantages and disadvantages of this new approach.Keywords: Long term behaviour, viscoplastic model, damage, deep claystone1. INTRODUCTIONIn November 1999, Andra started the construction work of the Meuse Haute-Marneunderground research laboratory (URL) (Figure 1) in the district of Bure, located inthe North-east of France. From 2000 until 2005, the construction of the experimentalsite has allowed us to study the radioactive waste repository feasibility in deepgeological formation. The main results are presented in the "dossier 2005" [1].The target horizon for the laboratory is a 135 m thick layer of argillaceous rock thatlies between about 420 and 555 meters below the surface at the URL site.Argillaceous rock contains a mixture of clay minerals (40 % to 45 %), silica andcarbonate-rich sedimentary.The construction of the URL itself serves a research purpose through monitoring ofthe excavation effects (?). The main goal of the geomechanical in situ investigationsis to understand the rock response to the excavation of underground engineeredstructures and to the development of the damaged zone. At short term (duringexcavation work), the major issues are to understand the rock mass deformations, thehydromechanical coupling, and the effect of excavation works on transport propertiesin the vicinity of the drifts. The long term behaviour remains also a key issue forrepository design and reversibility.At the main level of the laboratory, geomechanical measurements and EDZcharacterization have been performed (convergence, extensometer . . ) in drifts eitherparallel or perpendicular to the horizontal major stress. Armand et al. [2] describe theEDZ characterization and the induced fractures pattern observed during theexcavation works. They exhibit that high deformation rates appear in the fracturedarea [2]. Those in situ observations conducted Souley et al. [4] to propose a newmacroscopic viscoplastic model for Callovo-Oxfordian clay-stones based on fieldobservations and the previous models (short-term or long-term behaviour) in order toimprove the viscoplastic strain predictions around the drifts.Since the end of 2006, a new research program has started in the URL in whichAndra continues to study different excavation and support techniques in order tounderstand the effect on the EDZ extent and to optimize the excavation method. Thefeedback of previous experiments shows that "Mine-by-test" experiments are the bestway to increase the knowledge on drift behaviour. A "Mine-by-test" provides a largein situ characterization and is a good opportunity to develop and validate constitutivemodels and numerical tools able to predict the hydromechanical behaviour ofCallovo-Oxfordian clay-stones, as it was performed during the MODEX-REPEuropean project [3] around the main access shaft.The new excavations (GED drift, figure 1b) performed in 2008 provide the firstopportunity to test the new macroscopic viscoplastic model [4] thanks to blindprediction. This paper presents the experimental layout and the associated blindpredictions. The authors used this new model to perform 3D calculations using thereal construction steps. Those calculations show up the advantage of the new model.Comparisons with in situ data allow checking the efficiency of this numericalapproach.(a) (b)Figure 1: Meuse Haute Marne URL : (a) Location and geology,(purple: extension forecasted in 2012)Drifts and shaft network2. BRIEF DESCRIPTION OF THE RHEOLOGICAL MODELNumerous campaigns of laboratory tests (uniaxial/triaxial, mono/multi-stage creepand relaxation) have been undertaken for characterizing the mechanical andhydromechanical short and long-term behaviour of the argillites. As a result, severalconstitutive models were developed in the framework of MODEX-REP Europeanproject [3]. The new model [4] can be seen as a unification of two rheological modelsfor clay-stones: one for the short-term response is based on the extension of Hoek-Brown criterion to describe the damage in pre-peak phase (approached by the theoryof plasticity), failure and residual phase; the other for the long-term behaviouraccording to the modified Lemaître's model with creep threshold.The main characteristic of this model is the coupling of damage with creep behaviourof the argillites based on the obviousness of the damage impact on the viscoplasticstrain rates. In situ measurement exhibits high deformation rate in the fracture zoneobserved around the drift [2]. Those deformations are mainly due to the inducedfractures (EDZ) and their aperture. The modelling is performed in the framework ofcontinuum mechanics, and viscoplasticity in some way will take into account themechanical behaviour of this fractured zone.More precisely, in agreement with in situ observations, it was supposed that the post-failure material, in regards to its new microstructure, must have some creepcharacteristics which differ from those of the intact material. In particular theviscoplastic strain rate and the activation energy must reflect the failure of the clay-stones. For a damaged material (between the intact and failure states), a function ofinterpolation was proposed for the strain-hardening parameter since sufficient creeptests are not available on the damaged samples of clay-stones. The influence ofdamage on creep activation energy has been approached by an exponential function.Finally the coupling between the induced damage and the creep behaviour is onlyclarified in one way: (damage -¥ viscoplastic strain rates) since for the moment, wedo not consider the influence of viscoplastic strains on the damage threshold or moregenerally on the long-term strength of clay-stones. On the other hand, viscoplasticstrains modify the stress field which, in its turn, is corrected while it exceeds damagecriterion possibly changing indirectly EDZ extent. The set of constitutive equationsand their implementation in FLAC3D© code as well as verification and validationtests are widely presented in [4].3. EXPERIMENTAL LAYOUT3.1. In situ stress state and GED driftThe in situ stress state at the Meuse/Haute-Marne site has been measured bycomprehensive combined methods. The vertical stress profile is presently well-knownon the site. The horizontal stress anisotropy aH/ah is closed to 1.3 close to the mainlevel (-490 m) [5], respectively equal to 12.7 and 12.4 MPa for modelling task.The drift network grows following both horizontal principal stresses. GED drift is faraway from other drifts and excavated perpendicular to the horizontal major stress. It isexcavated with a pneumatic hammer. Supports consist of 2.2 m radial bolts, 10 cm ofsynthetic fibers reinforced shotcrete and sliding steel arches (installed every meter).The front is also reinforced with 11 synthetic anchors (12 m long) emplaced at thefront every 6 m. Excavation started in May 2008 and will be finalized by the end ofJanuary 2009.a,,=12. 7MPaothers section D (59.1 m),E3(61.1 m), F (63.5 m)SectionSe C (54.4 m)SectionSectcoi B (35.5 m)Sectionn A (19.5 m)Figure 2: Geometrical model for blind prediction of GED, meshing and boundary conditions3.2. Experiment layoutThe experiment layout consists of 6 convergence sections (with 5 convergencemeasurements per section, 4 extensometers 30 meter long, with 7 measurementsanchors (at 1, 2, 3.5, 5, 8, 15 and 30 m from the wall) and 4 extensometers 1 meterlong. A geological mapping of front (every 5 meters) and the structural analysis of allcored boreholes (even in borehole performed for other experiments) have been carriedout during excavation work to characterize the fracture zone. Extensometer andconvergence section have been installed during the excavation work. The otherboreholes will be drilled after the excavation. Multi-packer systems with 3 or 6chambers from the wall to 6 m deep, have although been emplaced to perform porepressure measurement and permeability tests. Those data are not presented becausethe numerical analysis is a purely mechanical analysis.4. CALCULATIONS AND RESULTS4.1. Geometry, boundary conditions and excavation sequenceIn relation to the symmetry of GED drift (70 m long and considered as isolated) andits orientation with respect to the initial stress state (parallel to ah), only the halfdomain is modelled. The geometrical model (150 m high, 57 m wide and 100 m long)shown in figure 2 consists of 574770 elements with following characteristics: 5 cmradially around the measurement sections A, B, C, D, E and F (located at 19.5, 35.5,51.5, 59, 61 and 63.5 respectively from the beginning of GED drift) and 40 cm axiallyon both sides of each measurement section. The real advance velocity during thedrilling of GED is used herein: the mean advance velocity is of 1 m/day except thebreak time to install materials.4.2. ResultsThe EDZ distribution around the GED drift is firstly examined. When the face ispositioned at sections B and C for example, fractured zones (from peak to the residualbehaviour) are not yet formed around the drift. From a face at 5 m after each section(that is to say two radii of gallery) to the end of excavation, the fractured zones extendfrom 0 to 29 cm depending on the position (floor, roof of drift side) and the section.Contrary, a damaged zone (pre-peak behaviour) is systematically formed as soon asthe GED face reaches the position of a given section (80, 110 and 120 cm,respectively at side, roof and floor of GED). In relation to anisotropy of the in situstress state, more damage is obtained in the vertical direction compared to thehorizontal ones (along aH) whereas the difference in EDZ geometry and extentbetween the floor and the roof is related to their geometries. The extent of damagedzone becomes 170, 260 and 270 cm respectively at side, roof and floor at the end ofexcavation.The evolutions of viscoplastic strains in time are also examined along vertical andhorizontal boreholes in section C (figure 3). If the maximum of deformation in thehorizontal direction is reached at the GED sides, the model predicts a maximum ofviscoplastic strain inside the rock matrix in the vertical directions. It is also noted thatthe amplitude of the viscoplastic deformations is well correlated to the intensity andthe extension of EDZ (i.e. high viscoplastic strains occur in the more damaged zones)in accordance with the philosophy of the model and the in situ observations. Inparticular, at the end of 10 years, the predicted viscoplastic strain rates at 2 m from theGED wall of 2e 12 and 4e12 s-1 respectively in the horizontal and vertical directions.4.3. Comparison with in situ dataThe analysis of measured and predicted convergences shows that in the verticaldirection and independently of the measurements section: (a) the short-term thevelocity of measured convergences are higher than those predicted, but at long-term,we can expect that the measured convergence velocities tend asymptotically towardsthe predictions; (b) the amplitude of measured convergences are higher than thoseVertical boreh ole (upward) Horizontal b orehole0 750 1500 2250 3000 3750Time from the extensometer section (days)Figure 3: Viscoplastic strains along vertical and horizontal boreholes (section C)nSecation A-•-Vert ical-numerica lHorizontal-numericalTime from section (days)S?•5|gIII vim iII 1VSecation B—*— Horizontal - measuresFigure 4: Comparison of calculated and measured convergence ratespredicted. In particular, calculation underestimates from 13 to 44% verticalconvergence respectively in sections B and C at the end of 80 days.For horizontal convergences we note that at 80 days after the passage of GED face toa given section, measured/predicted (in mm) convergences are of: 23/30; 18/39; 33/47respectively for the sections B and C. This illustrates the over-estimation character ofpredictive calculations in horizontal direction.The comparison of horizontal and vertical convergences rate is given as an examplefor section A and B (figure 4). It is thus noted that contrary to convergences, thepredicted convergences velocities are in agreement with those measured at court term.More precisely, of horizontal convergence velocities (average calculated on the"stages" and expressed in mm/j) in the form of measured/predicted are: 0.04/0.05;0.05/0.05 and 0.09/0.08 respectively in the sections have, B and C.5. CONCLUSIONS AND PERSPECTIVESThis paper presents firstly a 3D blind prediction of the behaviour of a GED driftoriented parallel to ah. The prediction is performed using new macroscopicviscoplastic model of Callovo-Oxfordian clay-stones which includes the impact ofdamaged and fractured zones in the near field behaviour.The comparison of the convergence predictions in 6 sections and the firstmeasurements indicates that the model underestimates the values of verticalconvergences and over-estimates horizontal convergences. On the other hand, theconvergences rates are well produced particularly in the horizontal direction as of the100 first days. The enriching of the model, particularly for the fractured zones(viscoplastic rates and modules), is in the course of reflexion and will integrate themeasurements of convergences and extensometric currently in acquisition.REFERENCES[1] Andra. Référentiel du site de Meuse/Haute-Marne - tome 2 - volume 5.Andra report no C.RP.ADS.04.0022, December 2005. (www.andra.fr)[2] Armand, G., Nussbaum, C, Cruchaudet, M. and Rebours, H. (2009)Characterisation of the Excavated Damaged Zone (EDZ) in the MeuseHaute-Marne underground research laboratory, In Proceedings of theInternational Conference on Rock Joints and Jointed Rock Masses, January4-9 ,2009 , TUCSON, USA[3] Su, K. (2003), Constitutive Models for the Meuse/Haute-Marne Argillites -MODEX-REP, European Commission - Nuclear science and technology,Contract n° FIKW-CT2000-00029, Deliverable 2-3[4] Souley, M., Su, K., Ghoreychi, M. and Armand, G. (2009), "A viscoplasticmodel including damage for deep argillaceous rocks" 1rst Int. Symposiumon Computational Geomechanics (ComGeo I), Juan-les-Pins, Cote d'Azur,France, April 29 - May 1st, 2009[5] Wileveau, Y., Cornet, F.H., Desroches, J. and Blumling, P. (2007) Completein situ stress determination in an argillite sedimentary formation, Phys. &Chem. of the Earth, 32, 866-878.

A viscoplastic model including damage for deep argillaceous rocks : blind predictions of drift behaviour

https://hal-ineris.ccsd.cnrs.fr/ineris-00973348

A viscoplastic model including damage for deep argillaceous rocks : blind predictions of drift behaviour

Abstract

Similar works

Full text

Available Versions

HAL-INERIS