GeoMod 2016 conference Montpellier, France | 17–20 October 2016 PROCEEDINGS GEOMOD 2016 26/10/2016 Organizing Committee (France): S. Dominguez (University of Montpellier, [email protected]), B. Maillot (University of Cergy-Pontoise), V. Cayol (University of Clermont-Ferrand), D. Arcay (University of Montpellier), B. Guillaume (University of Rennes), V. Pinel (University of Savoie Mont-Blanc), F. Graveleau (University of Lille). Technical Staff: C. Romano (University of Montpellier), A. Delplanque (University of Montpellier). Scientific Committee: C. Annen (University of Bristol, U.K.), A. Chemenda (University of Nice-Sophia-Antipolis, France), M. Cooke (University of Massachusett, USA), T. Dooley (University of Texas at Austin, USA), F. Funiciello (University of Roma Tre, Italy), K. Leever (GFZ, Potsdam, Germany), J. Malavieille (University of Montpellier, France), J.-C. Ringenbach (TOTAL, Pau, France), S. Schmalholz (University of Lausanne, Swiss). 1 GeoMod 2016 conference Montpellier, France | 17–20 October 2016 SESSIONS : S0 - What’s up in Modelling ? p.3 S1 - Geodynamics, Plate tectonics p.34 S2 - Coupling Tectonic and Surface processes p.100 S3 - Volcanoes: from the plumbing system to the eruptive plume p.155 S4 - Seismic cycle & Earthquake dynamics p.204 S5 - Rheology, strain localization, folding and faulting p.242 S6 - Dynamics of sedimentary Basins, Fluids & Georeservoirs p.281 GEOMOD2016 WebSite : http://geomod2016.gm.univ-montp2.fr/About.html GEOMOD2016 Facebook : https://www.facebook.com/geomod2016/ 2 GeoMod 2016 conference Montpellier, France | 17–20 October 2016 S0 - What’s up in Modelling ? 3 GeoMod 2016 conference Montpellier, France | 17–20 October 2016 Adequate constitutive description of geological materials is a major challenge for geomodeling: examples of deformation localization, fracturing, and faulting Alexandre Chemenda1, Daniel Mas1, Julien Ambre1, Jinyang Fan1, J.-P. Petit2, Stephane Bouissou1 1) University of Nice-Sophia Antipolis, Observatoire de la Côte d'Azur, Geoazur, Valbonne, France 2) University of Montpellier, Géosciences Montpellier, Montpellier, France Corresponding author: [email protected] S0- What’s up in Modelling ? (Keynote) Introduction: The mechanical (constitutive) models of geomaterials become progressively more sophisticated with the progress in our understanding of rock properties, which reflects the complexity of the behavior of these materials. For example, the experimental results from the test conducted under different loading configurations corresponding to the different Lode angles θ (axisymmetric compression, extension and true 3-D tests; Heard, 1960; Nguyen et al., 2011; Ingraham et al., 2013; Ma and Haimson, 2013) as well as a very recent theoretical analysis of these results (Chemenda and Mas, JMPS, 2016) show that θ strongly affects the inelastic response and failure of geomaterials. The θ-dependence of the rock properties as well as the evolution of the constitute parameters with inelastic deformation (damage) is typically ignored in numerical geomodeling and must be taken into account, notably when dealing with the material failure. It becomes particularly important to conduct a combined experimental and numerical (virtual) modeling complemented by the theoretical analysis and field observations to evaluate the realism of the virtual models. In this paper we present recent findings in the constitutive modeling and report the results from experimental studies and numerical modeling of faulting and fracturing resulting from a constitutive instability. Constitutive framework, experimental, and numerical models A pragmatic approach consists in formulation, based on the experimental data, of the models that are as simple as possible and that capture at the same time the essential features of rock behavior. How far can we simplify? The classical Mohr-Coulomb and Drucker-Prager models with constant internal friction coefficient , cohesion, and dilatancy factor are clearly oversimplified as in reality all these parameters are not constant but evolve with both the stress state and the material damage or inelastic strain (Fig. 1). Figure 1: Iso- sections of the yield surfaces with the superposed stress peak points (1) and the points corresponding to zero values of the hardening modulus (2). (3) is the linear approximation of the peak points corresponding to the failure envelopes. The slopes of these envelopes pk are different from = �̅ / �m. The 4 GeoMod 2016 conference GeoModMontpellier, France2016 | 17–20conference October 2016 Montpellier, France | 17±20 October 2016 numbers on the iso-γ sections of the yield surfaces are 103 × γ; ̅ is the von Mises stress, m is the mean stress, andparameters γ is the accumulated are not constant inelastic but strain evolve or withdamage both (Mas, the Chemenda,stress state IJRMMS,and the material2015). damage or inelastic strain (Fig. 1). Recent analysis of large data set for Granular Rock Analog Material GRAM1 and two Recentlimestones analysis has revealedof large thatdata notset onlyfor Granular ߙ defined Rock from Analog yield surfaceMaterials is GRAM1 not constant, and two but limestonesalso it is not has revealeddirectly relatedthat not to only the friction defined coefficient from yield ߙ ௣௞surfaces routinely is not defined constant, from but the also failure it is envelopesnot directly (from related the to thestress friction peaks) coefficient as is shown pkin routinelyFig. 1. defined from the failure envelopes (from the stress peaks) as is shown in Fig. 1. The details of constitutive description strongly affect the predictions of the material failure particularly Thewhen details the mean of constitutive stress ߪ௠ is description not very small strongly and theaffect failure the predictionsresults from of a thematerial material instability failure leadingparticularly to whenthe deformation the mean stress localization m is not. We very present small results and the from failure true results3-D experiments from a material showing instability the formation leading of to thefour deformation types of deformation localization. localization We present bands results with fromprogressively true 3-D increasingexperiments ߪ௠ :showing pure dilatant/dilatancy, the formation of fourshear types-dilatant of deformation, pure shear, localizationshear-compactive. bands Thesewith progressively bands have different increasing both morientation: pure dilatant/dilatancy, in the stress shear-dilatant,space and evolution. pure shear, Only shear-compactive. bands with dilatant These component bands have of differentdeformation both can orientation rapidly inevolve the stress to spacefractures and either evolution. opening Only or shearbands, whereaswith dilatant the bands component with compactive of deformation deformation can rapidlyundergo evolve a long to fracturesevolution either that may opening never resultor shear, in a whereasfracture formation.the bands with compactive deformation undergo a long evolution that may never result in a fracture formation. Numerical modeling integrating evolution of the constitutive parameters with stress and strain (as Numericalshown in Fig modeling. 1) and experimentallyintegrating evolution derived ofrelation the constitutive between the parameters yield and plasticwith stresspotential and functions strain (as shown(Mas and in Fig.Chemenda, 1) and experimentallyIJRMMS, 2015), derived allows relation not only between to reproduce the yield all aforementionedand plastic potential band/fracture functions (Mastypes, and but Chemenda, also more IJRMMS complicated, 2015), scenarios allows notwith only evolutio to reproducen of band all networks,aforementioned differential band/fracture band types,thickening but andalso propagationmore complicated observed scenarios in the experimental with evolution tests andof bandin nature networks, (e.g., Chemenda differential et al.,band thickeningTectophys .,and 2012). propagation The numerical observed models in theallow experimental also following tests in anddetail in the nature initiation (e.g., and Chemenda evolution et of al., Tectophys.fault systems, 2012). (Fig. The2) that numerical initiate via models deformation allow also banding following of different in detail types the (Chemenda initiation and et al., evolution 2016). of fault systems (Fig. 2) that initiate via deformation banding of different types (Chemenda et al., 2016). Sandbox model (Naylor et al., 1986) Numerical model Figure 2: Comparison of the evolution of the Riedel-type faulting in analogue and numerical models Figure 2. Comparison of the evolution of the Riedel-type faulting in analogue and numerical models Keywords:! Rock mechanical (constitutive) properties, rock testing, Lode angle, deformation bifurcation, strain localization, fracturing, faulting, experimental and numerical modeling, natural ! deformation bands. "#$%&'()! Rock mechanical (constitutive) properties, rock testing, Lode angle, deformation bifurcation, strain localization, fracturing, faulting, experimental and numerical modeling, natural deformation bands. 5 GeoMod 2016 conference Montpellier, France | 17–20 October 2016 Laboratory characterization of thermal plumes at high Rayleigh numbers Danielle Brand1 and Anne Davaille1 1) Université Paris-Saclay, Lab. FAST, Orsay, France Corresponding author: [email protected] S0- What’s up in Modelling ? (PS7) Introduction: Thermal plumes are gravitationally buoyant instabilities which form when a layer of fluid is heated from below. Therefore, they are ubiquitous