A. Chemenda

A. Chemenda
University of Nice Sophia Antipolis | UNS · Département des Sciences de la Terre

PhD

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86
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Publications

Publications (86)
Article
It is known that rock fracture includes inelastic straining or damage that should localize at a certain loading stage and result in fracture initiation. The details of this process are not clear, and it is frequently omitted in the models by imposing the initial microcracks (seeds) with certain lengths and orientations. Here we investigate 2-D syst...
Article
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Fracturing (jointing) affects large volumes of rocks and strongly impacts their mechanical stability and permeability. In layered sedimentary basins, the fractures typically form subparallel sets with different fracture spacing S. This parameter has been extensively studied both in the field and in mechanical models in relation to the thickness T o...
Article
True 3D rock tests have revealed more complex (than axisymmetric conventional tests) constitutive behaviors of geomaterials which depend on the Lode angle and intermediate principal stress \(\sigma_{2}\). These tests, however, are subject to significant errors related to the end effects. It is important to understand which part of the stress–strain...
Article
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The overwhelming majority of experimental and numerical tests show the dependence of mechanical response on discontinuities (such as joints, faults, and bedding plane). In this study, fracture process is numerically investigated using finite‐difference method. A quasi‐continuum model (assuming that the real rock mass represents the sum of intact ro...
Article
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Experimental data show that inelastic straining occurs even at very low pressure before and during brittle fracturing. This process is therefore investigated within the framework of elastoplasticity using 2‐D, three‐layer finite difference modeling. The constitutive model includes both tensile and shear failure mechanisms coupled at the level of th...
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We investigate the deformation localization at brittle–ductile transition in axisymmetric compression tests of rock analogue material GRAM1 made of bonded rigid particles. This transition in rocks (as well as in GRAM1) is recognized by the formation of a network of conjugate deformation localization bands in the postmortem rock samples and by a sha...
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Fracture process is investigated using finite-difference simulations with a new constitutive model. It is shown that both geometry and fracture mechanism itself depend on the preexisting heterogeneities that are stress concentrators. In the brittle regime (low pressure, P), Mode-I fractures propagate normal to the least stress σ3 from the imposed w...
Article
In order to analyze the healing effectiveness of rock salt cracks affected by the applied stresses and time, we used the ultrasonic technology to monitor the ultrasonic pulse velocity (UPV) variations for different initial stress-damaged rock salts during self-healing experiments. The self-healing experiments were to create different conditions to...
Article
The majority of experimental rock fatigue tests have been conducted with the continuous cyclic loading path. In this paper we report the results from the fatigue tests of salt with discontinues cyclic loading path containing zero loading stress intervals (ZLIs) of different duration. We show that the application of such intervals strongly changes t...
Article
The overwhelming majority of experimental tests on rocks have only been conducted for a single value of the Lode angle corresponding to the axisymmetric compression (AC). There are now sufficiently extensive data sets from both AC and axisymmetric extension (AE) tests (corresponding to two extreme values) for two materials (synthetic rock analogue...
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The initiation and the initial evolution of a strike-slip fault are modeled within an elastoplasticity constitutive framework taking into account the evolution of the hardening modulus with inelastic straining. The initial and boundary conditions are similar to those of the Riedel shear experiment. The models first deform purely elastically. Then d...
Article
Complexity of the mechanical behavior of geomaterials makes it very difficult to formulate constitutive models (both at micro- and macro-scales) valid for different loading conditions and deformation regimes. To make progress in understanding this complexity, we take advantage of the large set of data for the synthetic rock analog GRAM1, a granular...
Article
It is known that there is stress concentration at specimen ends during experimental rock tests. This causes a deviation of the measured nominal (average) stresses and strains from the actual ones, but it is not completely clear how strong it could be. We investigate this issue by numerical modeling of the hydrostatic tests using a reasonably simple...
Article
Networks of localized conjugate compactive shear bands with large dihedral angle (corresponding to so-called shear-enhanced compaction bands) were generated in 3-layer plane strain finite-difference models. The central layer has elastic–plastic properties with a small positive internal friction coefficient, negative dilatancy factor, and the harden...
Article
The dilatancy is as important property of rock-type (granular, frictional, cohesive, and dilatant) materials as the internal friction, but it is generally ill-constrained and is rarely taken into account in applications, being set to zero. Theoretical analysis shows that the dilatancy factor β strongly affects the onset of the deformation instabili...
Article
Full-text available
A scaled elasto-plastic lithosphere model lying upon a liquid substratum is subjected to a uni-axial horizontal tension. In a homogeneous plate extension localises along a linear zone (rift) oriented at an angle of ~60 to the tension axis. This orientation is preserved even when the divergent displacement of the opposite plate boundaries is not pla...
Article
Both oedometric and plane-strain tests were performed with parallelepipedic samples made of synthetic granular, cohesive, frictional and dilatant rock analogue material GRAM2. For the first time parallel sets of fractures that have all the characteristics of natural joints were reproduced in the laboratory. The fractures are regularly spaced, norma...
Article
Refining Constitutive Characterization of Geomaterials and Identifying Their Rupture Mechanisms in Natural Conditions; Montpellier, France, 7-8 September 2011 Results from rock testing and geological observations of different types of deformation bands and fractures highlight the problem of understanding the underlying formation mechanisms from gra...
Article
An accurate analysis of fracture and cleavage anisotropies along two landslides in the Argentera massif (French Southern Alps) was performed in order to relate the fracturing mode to the rock slope failure state. The mature La Clapière landslide and the incipient Isola Landslide were investigated. In both cases, the gneissic rock schistosity was fo...
Article
Joints are pervasive fractures strongly affecting the reservoir permeability and seals integrity. They are currently interpreted as mode I cracks forming normal to the minimal tensile effective stress S3. This view is challenged by the results of both axisymmetric and polyaxial (true 3-D) extension experiments carried on rock analogue materials whe...
Article
Dilatancy bands were recently obtained in conventional axisymmetric extension tests on a synthetic physical rock analogue (granular, frictional, cohesive and dilatant) material GRAM1 at a relatively low mean stress σ within range σd < σ < σs , where σd and σs are experimentally constrained values (Chemenda et al., JGR, 2011). The walls of the opene...
Article
Compactive shear bands with different ratio of compactive to shear inelastic deformation were recently studied in detail in different regions within the porous rocks. Among them are nicely exposed networks of conjugate cataclastic bands formed in a single tectonic event in the "Bassin du Sud-Est" (Provence, France) in Cretaceous sandstones. Microan...
Article
Terminology on fracture and discontinuities in geological objects mainly relies on distinguishing between tabular and sharp forms of deformation localization/failure structures (Aydin et al, JSG 2006; Shultz and Fossen, AAPG, 2009). On this basis joints (considered as mode I fractures) and dilation bands (very rarely observed) are distinguished amo...
Article
Networks of localized compactive and isovolumetric shear bands were generated in 2-D finite-difference models. They reproduce the most striking feature of the evolution of natural deformation bands characterized by compactive (or non-dilatant) inelastic volumetric deformation, i.e., the band thickening from the flanks by incorporation of the initia...
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Full-text available
Characterization and Formation Mechanisms of Deformation Localization Bands(Shear, Compaction, and Dilatancy): Field and Experimental Data,Theoretical Analysis and Numerical Models;Montpellier, France, 9-10 May 2011 . The origin of fractures and discontinuities in rocks has been for decades a subject of common interest in both the academic world an...
Chapter
In this chapter we present a review of 2D, and 3D, purely mechanical and thermo‐mechanical experimental models of arc–continent collision obtained using the modeling technique pioneered by A. Chemenda. Also presented are earlier models of oceanic and continental subduction which led to the development of the arc–continent collision experiments. Phy...
Article
Full-text available
Fractures or discontinuities perpendicular to the least stress 3 were generated in a synthetic rock analogue (granular, frictional, cohesive, and dilatant) material in axisymmetric extension tests. These fractures are of two types defined by the mean stress . When is very small, the fractures form through the mode I cracking at tensile 3 equal to t...
Article
Extension fractures of two types defined by the mean stress σ were generated in a synthetic rock analogue material. When σ is very small, the fractures are mode I cracks with smooth surfaces. At higher σ, these surfaces have plumose topography, with the amplitude increasing with σ. Both SEM observations and mechanical measurements show that fractur...
Article
Full-text available
Catastrophic deep-seated landslides (DSL) are generally considered to be the result of large slope deformations also known as deep-seated gravitational slope deformation (DSGSD). This paper aims to build a synthesis of multiple studies made in the Tinée Valley (southern French Alps) to assess the geometrical, kinematical, mechanical and chronologic...
Article
Based on the theoretical analysis and finite–difference simulations, we study the onset and evolution of tabular compaction bands. In numerical models the bands are initiated as constitutive instabilities resulting from the deformation bifurcation. Then some bands are dying, while others continue to evolve accumulating the inelastic deformation/dam...
Article
An extensive program of axisymmetric compression and extension tests was performed with synthetic granular, cohesive, frictional and dilatant, low strength/rigidity rock analogue material. The program was motivated in particular by the lack of rock tests under extension, and was aimed at a detailed characterization of the constitutive properties, a...
Article
The onset and evolution of tabular compaction bands is studied based on the discontinuous bifurcation analysis and finite-difference simulations. In numerical models, the bands are initiated as constitutive instabilities resulting from the deformation bifurcation. Band spacing, length and aspect strongly depend on the constitutive parameters and pa...
Article
The mechanism of quasi-brittle fracture/rupture remains one of the central problems in different domains of material science/mechanics including geomechanics. There are basically two approaches to this problem. One is the fracture mechanics dealing with stability conditions of cracks characterized by a strong stress concentration at the tips causin...
Article
Full-text available
Extension fractures/discontinuities perpendicular to the least stress 3 σ were generated in a synthetic physical rock analogue material (granular, frictional, cohesive and dilatant) in axisymmetric extension tests. These fractures are of two types defined by the mean stress σ . When σ is very small, the fractures form through mode I cracking at 3 σ...
Article
A finite difference two-dimensional model with Hooke–Mohr–Coulomb properties and topography derived from the DEM are used to reproduce the La Clapière landslide. The principal factor defining the gravity-driven destabilization of the model is a gradual reduction in the cohesion. This reduction simulates a degradation of the material properties with...
Article
The bifurcation analysis of compaction banding is extended to the formation of a tabular discrete compaction-band array. This analysis, taken together with the results of finite-difference simulations, shows that the bifurcation results in the formation of intermittent loading (elastic–plastic) and unloading (elastic) bands. The obtained analytical...
Article
Both 3-D physical modeling and 2-D numerical modeling were used to analyze the development of Deep-Seated Gravitational Slope Deformations. We focused especially on the link between fracturing and morphological features such as Sagging/Sackung. Physical modeling was performed by using properly scaled analogue materials as well as an original vertic...
Article
Spatial distribution of UHP/LT terrains suggests that their exhumation is essentially a three-dimensional process that occurs only locally in specific sites along mountain belts. On the other hand, the continental subduction resulting in the formation of UHP/LT rocks takes place along the whole belt. The previously performed by the authors 2-D ther...
Article
Full-text available
The Paleozoic French Variscan Belt in Massif Central and Massif Armoricain is a collision belt that provides a good example of a suture zone where ophiolites are rare, and the frontal (i.e., the magmatic arc) part of the upper plate is not present. In the lower plate (or Gondwana), the continental rocks are subdivided into an Upper Gneiss Unit (UGU...
Article
Full-text available
A mono-shear-band bifurcation analysis is extended to the formation of shear-band network affecting a finite brittle body. This analysis, along with the results of numerical simulations, suggests the following description of the bifurcation process. It starts when the hardening modulus h reaches a critical value hmax which has proved to be the same...
Article
Full-text available
Gravitational slope failures and associated rock mass movements can be observed at various scales in the same area. It seems obvious that the different movement scales should be interrelated, but their relationships are poorly understood. We address this problem using 3-D physical modeling. Experiments were conducted with mechanically homogeneous m...
Article
Full-text available
1] A new technique for physical (experimental) modeling of landsliding and the first results are presented. The technique is based on the use of new elasto-brittle-plastic analogue materials and an original vertical accelerator device enabling an increase in the ''gravity acceleration.'' This technique allows slope stability to be addressed in a fu...
Article
Full-text available
Using a new 3-D physical modelling technique we investigated the initiation and evolution of large scale landslides in presence of pre-existing large scale fractures and taking into account the slope material weakening due to the alteration/weathering. The modelling technique is based on the specially developed properly scaled analogue materials, a...
Article
Thermo-mechanical physical modelling of continental subduction is performed to investigate the exhumation of deeply subducted continental crust. The model consists of two lithospheric plates made of new temperature sensitive analogue materials. The lithosphere is underlain by liquid asthenosphere. The continental lithosphere contains three layers:...
Article
Full-text available
We perform thermo-mechanical laboratory experiments designed to explore the behaviour of the volcanic arc during intra-oceanic arc–continent collision following oceanic subduction and subsequent back-arc opening. The overriding oceanic lithosphere is made of two layers representing the oceanic crust and the lithospheric mantle. This lithosphere car...
Article
Spatial distribution of metamorphic terrains evidences that the exhumation of UHP/LT rocks is essentially a 3-D process. These rocks outcrop only in some specific places: near a lateral termination of the mountain belt (Western Himalaya, Oman), in the vicinity of a lithospheric faults (Dabie Shan) or where the belt has a strong curvature (Western A...
Article
Continental rifting is treated as a mechanical instability developing under horizontal tectonic tension. The instability results in strain localization and the formation of a neck, which is interpreted as a rift zone. At the scale of the whole lithospheric plate, this process occurs in plane-stress conditions and can therefore be modelled to a firs...
Article
A tectonic model of Alpine Corsica is proposed based on geological studies. Its evolution starts after the Jurassic with intraoceanic subduction, followed by mid-Cretaceous subduction of the European continental margin under the oceanic segment of the Adriatic plate. After subduction of the continental crust to a depth of ≈ 150 km, slices of crusta...
Article
Thermo-mechanical physical modelling of continental subduction is performed using new temperature sensitive analogue materials to model the lithospheric layers. The initially horizontal lithosphere model is underlain by the liquid asthenosphere and subjected to a constant vertical thermal gradient. The lithosphere contains three layers: the very we...
Article
We performed two-dimensional finite-element numerical modeling of subduction to study the deformation and failure pattern of an overriding plate. This plate has elasto-plastic rheology with strain weakening and contains a "volcanic arc" represented in the model as a thinned and rheologically weakened zone. The subducting plate is not modeled direct...
Article
A thermo-mechanical experimental modelling of the continental subduction is per- formed using new temperature very sensitive analogue materials to model the litho- sphere. The model which includes initially horizontal lithosphere underlain by the liquid asthenosphere is subjected to a constant vertical thermal gradient. The litho- sphere contains t...
Article
A 2-D physical and finite-element numerical modelling of arc continent collision was performed to study the deformation and failure of the overriding lithosphere. The experimental technique allowed us to model the whole subduction/collision process from oceanic subduction to deep subduction of the continental crust. With the numerical approach we h...
Article
Both the analysis of the geological data and the results from 2D and 3D experimental modelling of arc–continent collision in Taiwan reveal the following major stages in this process: (1) failure and thickening of the subducting crust of the Chinese continental margin under the frontal part (accretionary prism) of the Philippine Sea Plate (PSP) sinc...
Article
Two-dimensional finite element numerical modelling is applied to study the deformation and failure of the overriding plate during arc–continent collision (continental margin subduction). This plate has elasto-plastic rheology with strain weakening and contains a 'volcanic arc' with thinned and weakened lithosphere. The overriding plate deforms due...
Article
Full-text available
Physical modeling of oblique subduction is performed to study the mechanism of strain partitioning. The model is two-layer and includes the elasto-plastic lithosphere (the overriding and subducting plates) and the low-viscosity liquid asthenosphere. The subduction is driven by a push force from a piston and a pull force when the density contrast Ap...
Article
A two-dimensional thermo-mechanical laboratory modelling of continental subduction was performed. The subducting continental lithosphere includes a strong brittle upper crust, a weak ductile lower crust, and a strong upper mantle. The lithosphere is underlain by a low viscosity asthenosphere. Subduction is produced by a piston (push force) and the...
Article
A two-dimensional thermo-mechanical laboratory modelling of continental subduction was performed. The subducting continental lithosphere includes a strong brittle upper crust, a weak ductile lower crust, and a strong upper mantle. The lithosphere is underlain by a low viscosity asthenosphere. Subduction is produced by a piston (push force) and the...
Article
A new evolutionary geodynamic model of Devonian continental subduction and exhumation of high-pressure/low-temperature metamorphic rocks in the southern Urals is proposed based on the results of physical modelling, geological and geophysical data, and on the comparison of this belt with other orogens. The model includes the following principal phas...
Article
2-D and 3-D physical modelling of lithospheric convergence in the Luzon-Taiwan-Ryukyu region is performed with properly scaled laboratory models. The lithospheric model consists of two parts, continental (the Asian Plate, AP) and oceanic (the Philippine Sea Plate, PSP). The oceanic lithosphere has one layer, while the continental lithosphere includ...
Article
The physical model presented reveals two principal regimes of continental subduction: a highly compressional (HC) regime and a low compressional (LC) regime characterised by high and low pressure between the overriding and subducting plates, respectively. The pressure is inversely proportional to the pull force, which depends on the difference betw...
Article
The Urals are a 3,000 km long, N-S Palaeozoic mountain belt separating Europe from Asia. In the southern part of the belt, there is a narrow (10-20 km wide) strip of HP metamorphic rocks (eclogites and blue schists) mainly of continental and probably partly of oceanic origin. These rocks outcrop along the western side of a major suture zone, the Ma...
Article
Properly scaled physical modelling of the subduction of continental lithosphere is performed with a three-layer lithospheric model. The model includes a strong upper crust, a weak ductile lower crust, and a strong mantle part. The lithosphere is underlain by a low-viscosity asthenosphere. Subduction is produced by a piston (push force) and the pull...
Article
A properly scaled thermo-mechanical experimental model of slow seafloor spreading is developed to investigate the mechanism of lithosphere accretion. The melt of a specially fabricated hydrocarbon compositional system is cooled from above in a tank. The crystallizing upper layer possesses semiplastic-semibrittle properties. Horizontal tension of th...
Article
We considered the origin and evolutionary conditions for the axial magma chamber (AMC) in the rift zone of mid-oceanic ridges (MOR), in the framework of the continuous-discrete spreading model. Calculations show that the depth to the chamber top depends on spreading rate, periodicity of the tectono-magmatic cycle, fracturing in the crust, hydrother...
Chapter
As pointed out in the previous chapter, the main difficulties in the physical modeling are associated with the creation of model materials and experimental conditions that satisfy the physical similarity conditions. Some subduction-related processes have been already modeled in laboratory using different techniques which have allowed one to achieve...
Chapter
In Section 4.11 we discussed the mechanisms for increasing compression of the lithosphere in a subduction zone. These mechanisms are; subduction of young lithosphere, an increase in subduction rate, subduction of different asperities (seamounts, ridges) and plateaux. The most intensive compression occurs during subduction of the continental margin,...
Chapter
Since the large spatial and time scales of geodynamic processes renders their direct observation and investigation impossible in most cases, the methods of quantitative modeling become very important. Frequently, modeling is the only way to get some ideas about geological phenomena. Most popular is mathematical modeling. Another method, physical (s...
Chapter
The main difference between mechanics of the classical subduction of oceanic lithosphere and the subduction (consumption) of continental lithosphere in the collision zones beneath either continental or oceanic lithosphere, is defined by the presence of a thick continental crust in the latter case. High buoyancy of the crust prevents it from being p...
Chapter
More then 80% of seismic energy in subduction zones is released in thrust type earthquakes with the axis of maximum compression oriented transverse to the subduction zones [Balakina1984]. This is consistent with the convergence of the lithosphere in these zones. In spite of this, it is not obvious that the general stress regime of the lithosphere i...
Chapter
In all experiments presented in the previous chapter densities of the lithosphereρland the asthenosphere ρaare equal. Such a condition corresponds to reality only to a first approximation. In fact, ρl may be either less than or greater than ρa. The lithospheric density depends on many factors, the “thermal” age being the most important one[Oxburgh...
Article
This book is devoted to the quantitative physical modeling of subduction and subduction-related processes. It presents a coherent description of the modeling method (including similarity criteria, and a novel applied experimental technique), results from model experiments, theoretical analysis of results on the basis of continuum mechanics, and the...
Article
Results of physical modeling of the lithosphere subduction are reported. Tension of the overriding lithosphere is found to arise in situations where some forces tend to separate the plates in the subduction zone. Such conditions can occur when (1) there is subduction of an old (dense) plate, (2) a horizontal asthenospheric (mantle) flow acts on the...
Article
Physical (mechanical) modeling of continental collision is performed with a 4-layered mantle model. Compositionally distinct layers of hydrocarbons are used to model a lithosphere which consists of two crustal layers (the upper one quasi-brittle, the lower one plastic) and a plastic mantle layer. The lower crustal layer, the “crustal asthenosphere”...
Article
A two-layered experimental mantle model based on the criteria of similarity is developed that combines an elasticoplastic lithosphere and low-viscosity asthenosphere and is used to model subduction. The mechanical model consists of a hydrocarbon compositional system organized with an upper layer of strong viscous material and a lower layer of less...
Article
On the basis of results of physical modelling and an analysis of the relevant geological and geophysical data, the mechanism and regularity of rifting are studied. As a rule, rifting develops in extensive and long-living “hot” regions characterized by a reduced thickness of lithosphere. Rifts develop due to regional extension of the lithosphere in...
Article
Physical modelling and geodynamic analysis have been carried out concerning the formation and evolution of overlapping spreading centers (OSCs) with fast spreading rates. Crust and underlying magma chamber were modelled by (solidified and melted respectively) a composite system composed of mineral oils, solid hydrocarbons and surface-active substan...
Article
Several geodynamic situations involve strong horizontal compression of the lithosphere that produces a high degree of its deformation or failure. This is especially true of active continental margins, collision zones, and oceanic transform faults in which there is a compressive force component. The present paper describes the physical modeling of s...
Article
A fine structure has recently been identified in ocean rifts with high spreading rates. The mechanism of quasibrittle failure of the basaltic layer (the crust) in the axial zone of a rift above a magma chamber as a result of development and interaction of macrojoints (cracks) in it has already been invoked in the literature as a possible explanatio...
Article
In number of orogens (e.g. Alps, Norwegian Caledonides, Dabie Shan) exhumation of UHP/LT rocks was followed by HT metamorphism and magmatic events both suggesting heating of the crust. We present a geodynamical model based on the thermo-mechanical analogue experiments that allow us to account for this relation between the exhumation and temperature...

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