A multiscale work-analysis approach for geotechnical structures     

Hao Xiong  Zhen-Yu Yin  François Nicot 《国际地质力学数值与分析法杂志》2019,43(6):1230-1250

This paper presents a second-order work analysis in application to geotechnical problems by using a novel effective multiscale approach. To abandon complicated equations involved in conventional phenomenological models, this multiscale approach employs a micromechanically-based formulation, in which only four parameters are involved. The multiscale approach makes it possible a coupling of the finite element method (FEM) and the micromechanically-based model. The FEM is used to solve the boundary value problem (BVP) while the micromechanically-based model is utilized at the Gauss point of the FEM. Then, the multiscale approach is used to simulate a three-dimensional triaxial test and a plain-strain footing. On the basis of the simulations, material instabilities are analyzed at both mesoscale and global scale. The second-order work criterion is then used to analyze the numerical results. It opens a road to interpret and understand the micromechanisms hiding behind the occurrence of failure in geotechnical issues.  相似文献   

Multiscale approach to geo‐composite cellular structures subjected to rock impacts     

François Nicot  Philippe Gotteland  David Bertrand  Stéphane Lambert 《国际地质力学数值与分析法杂志》2007,31(13):1477-1515

Geo‐composite cellular structures are an efficient technological solution for various applications in civil engineering. This type of structure is particularly well adapted to resisting rockfalls and can act as a defensive structure. However, the design of such structures is for the most part empirically based; this lack of research‐based design stagnates optimization and advanced development. In this paper, the mechanical behaviour of a geo‐composite cellular structure is investigated using a multi‐scale approach, from the individual cell made up of an assembly of rocky particles contained in a wire netting cage to the entire structure composed of a regular array of cells. Based on discrete modelling of both the cell and structure scales, a computational tool has been developed for design purposes. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Bifurcation and second‐order work in geomaterials     

François Nicot  Félix Darve  Huynh Dat Vu Khoa 《国际地质力学数值与分析法杂志》2007,31(8):1007-1032

In this paper, the ability of a material rate‐independent system to evolve toward another mechanical state from an equilibrium configuration, with no change in the control parameters, is investigated. From a mechanical point of view, this means that the system can spontaneously develop kinetic energy with no external disturbance from an equilibrium state, which corresponds to a particular case of bifurcation. The existence of both conjugate incremental strain and stress such that the second‐order work vanishes is established as a necessary and sufficient condition for the appearance of this bifurcation phenomenon. It is proved that this fundamental result is independent of the constitutive relation of the rate‐independent material considered. Then the case of homogeneous loading paths is investigated, and, as an illustration, the subsequent results are applied to interpret the well‐known liquefaction observed under isochoric triaxial loading conditions with loose granular materials. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Monitoring above-zone temperature variations associated with CO2 and brine leakage from a storage aquifer     

Mehdi Zeidouni  Jean-Philippe Nicot  Susan D. Hovorka 《Environmental Earth Sciences》2014,72(5):1733-1747

CO₂ injection in saline aquifers induces temperature changes owing to processes such as Joule–Thomson cooling, endothermic water vaporization, exothermic CO₂ dissolution besides the temperature discrepancy between injected and native fluids. CO₂ leaking from the injection zone, in addition to initial temperature contrast due to the geothermal gradient, undergoes similar processes, causing temperature changes in the above zone. Numerical simulation tools were used to evaluate temperature changes associated with CO₂ leakage from the storage aquifer to an above-zone monitoring interval and to assess the monitorability of CO₂ leakage on the basis of temperature data. The impact of both CO₂ and brine leakage on temperature response is considered for three cases (1) a leaky well co-located with the injection well, (2) a leaky well distant from the injector, and (3) a leaky fault. A sensitivity analysis was performed to determine key operational and reservoir parameters that control the temperature signal in the above zone. Throughout the analysis injection-zone parameters remain unchanged. Significant pressure drop upon leakage causes expansion of CO₂ associated with Joule–Thomson cooling. However, brine may begin leaking before CO₂ breakthrough at the leakage pathway, causing heating in the above zone. Thus, unlike the pressure which increases in response to both CO₂ and brine leakage, the temperature signal may differentiate between the leaking fluids. In addition, the strength of the temperature signal correlates with leakage velocity unlike pressure signal whose strength depends on leakage rate. Increasing leakage conduit cross-sectional area increases leakage rate and thus increases pressure change in the above zone. However, it decreases leakage velocity, and therefore, reduces temperature cooling and signal. It is also shown that the leakage-induced temperature change covers a small area around the leakage pathway. Thus, temperature data will be most useful if collected along potential leaky wells and/or wells intersecting potential leaky faults.  相似文献   

Chloritöid-pyrophyllite-rectorite facies rocks from Brittany,France     

S. Paradis  B. Velde  E. Nicot 《Contributions to Mineralogy and Petrology》1983,83(3-4):342-347

Electron microprobe analyses of minerals in low grade metamorphic sandy black shales of middle Paleozoic age indicate that chemical equilibrium was closely approached in authigenic ferro-magnesian or alkali-bearing phases while aluminum silicate minerals appear to have reacted at a slower rate. The K for Mg-Fe in chlorite-chloritöid pairs is 0.19, the latter phase being iron-rich. The pseudomorphism of detrital white micas produces kaolinite, pyrophyllite and intimate mixtures of muscoviteparagonite. New phases forming in other sites include chlorite, chloritöid and rectorite which is an ordered paragonitebeidellite mixed layered phase. These minerals were formed at temperatures below 280° C. This is just above the stability of the illite-smectite mixed layered minerals which have an ISII ordering sequence (85 to 95% illite). It was noted that ferromagnesian minerals attain chemical equilibrium on a thin-section scale while the aluminous phases often seem to respond to chemical potentials operative on a submillimetric scale.  相似文献   

From micro scale to boundary value problem: using a micromechanically based model     

Xiong  Hao  Nicot  François  Yin  Zhenyu 《Acta Geotechnica》2019,14(5):1307-1323

Acta Geotechnica - A 3D multi-scale approach is presented to investigate the mechanical behavior of a macroscopic specimen consisting of a granular assembly, as a boundary value problem. The core...  相似文献   

Controls on Methane Occurrences in Shallow Aquifers Overlying the Haynesville Shale Gas Field,East Texas          下载免费PDF全文

Jean‐Philippe Nicot  Toti Larson  Roxana Darvari  Patrick Mickler  Michael Slotten  Jordan Aldridge  Kristine Uhlman  Ruth Costley 《Ground water》2017,55(4):443-454

Understanding the source of dissolved methane in drinking‐water aquifers is critical for assessing potential contributions from hydraulic fracturing in shale plays. Shallow groundwater in the Texas portion of the Haynesville Shale area (13,000 km²) was sampled (70 samples) for methane and other dissolved light alkanes. Most samples were derived from the fresh water bearing Wilcox formations and show little methane except in a localized cluster of 12 water wells (17% of total) in a approximately 30 × 30 km² area in Southern Panola County with dissolved methane concentrations less than 10 mg/L. This zone of elevated methane is spatially associated with the termination of an active fault system affecting the entire sedimentary section, including the Haynesville Shale at a depth more than 3.5 km, and with shallow lignite seams of Lower Wilcox age at a depth of 100 to 230 m. The lignite spatial extension overlaps with the cluster. Gas wetness and methane isotope compositions suggest a mixed microbial and thermogenic origin with contribution from lignite beds and from deep thermogenic reservoirs that produce condensate in most of the cluster area. The pathway for methane from the lignite and deeper reservoirs is then provided by the fault system.  相似文献   

Controls on Methane Occurrences in Aquifers Overlying the Eagle Ford Shale Play,South Texas          下载免费PDF全文

Jean‐Philippe Nicot  Toti Larson  Roxana Darvari  Patrick Mickler  Kristine Uhlman  Ruth Costley 《Ground water》2017,55(4):455-468

Assessing natural vs. anthropogenic sources of methane in drinking water aquifers is a critical issue in areas of shale oil and gas production. The objective of this study was to determine controls on methane occurrences in aquifers in the Eagle Ford Shale play footprint. A total of 110 water wells were tested for dissolved light alkanes, isotopes of methane, and major ions, mostly in the eastern section of the play. Multiple aquifers were sampled with approximately 47 samples from the Carrizo‐Wilcox Aquifer (250‐1200 m depth range) and Queen City‐Sparta Aquifer (150‐900 m depth range) and 63 samples from other shallow aquifers but mostly from the Catahoula Formation (depth <150 m). Besides three shallow wells with unambiguously microbial methane, only deeper wells show significant dissolved methane (22 samples >1 mg/L, 10 samples >10 mg/L). No dissolved methane samples exhibit thermogenic characteristics that would link them unequivocally to oil and gas sourced from the Eagle Ford Shale. In particular, the well water samples contain very little or no ethane and propane (C1/C2+C3 molar ratio >453), unlike what would be expected in an oil province, but they also display relatively heavier δ¹³C_methane (>?55‰) and δD_methane (>?180‰). Samples from the deeper Carrizo and Queen City aquifers are consistent with microbial methane sourced from syndepositional organic matter mixed with thermogenic methane input, most likely originating from deeper oil reservoirs and migrating through fault zones. Active oxidation of methane pushes δ¹³C_methane and δD_methane toward heavier values, whereas the thermogenic gas component is enriched with methane owing to a long migration path resulting in a higher C1/C2+C3 ratio than in the local reservoirs.  相似文献   

Second‐order work analysis for granular materials using a multiscale approach     

François Nicot  Nejib Hadda  Félix Darve 《国际地质力学数值与分析法杂志》2013,37(17):2987-3007

It has been established that the second‐order work criterion is a general necessary condition for all instabilities by divergence in rate‐independent granular materials. The relation between the values of discrete second‐order work at the intergranular contact point level and its global macroscopic value is recalled at the beginning of this paper. Then, the basic purpose of the paper is tackled by an analysis of the main features of second‐order work criterion in relation with the granular microstructure. For that, it is considered a novel micromechanical model (the so‐called ‘H‐microdirectional model’), which has the property to involve three scales: grain scale, mesoscale with a specific granular configuration and continuum mechanics macroscale. Eventually, these exhibited features (a bifurcation stress domain and some instability cones) are qualitatively compared with the ones provided by direct numerical simulations issued from a discrete element model. The ultimate goal is to analyse what happens at the granular scale, when the macrosecond‐order work is vanishing at the macrolevel. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

PILOT: a balloon-borne experiment to measure the polarized FIR emission of dust grains in the interstellar medium     

J-Ph. Bernard  P. Ade  Y. André  J. Aumont  L. Bautista  N. Bray  P. de Bernardis  O. Boulade  F. Bousquet  M. Bouzit  V. Buttice  A. Caillat  M. Charra  M. Chaigneau  B. Crane  J.-P. Crussaire  F. Douchin  E. Doumayrou  J.-P. Dubois  C. Engel  P. Etcheto  P. Gélot  M. Griffin  G. Foenard  S. Grabarnik  P. Hargrave  A. Hughes  R. Laureijs  Y. Lepennec  B. Leriche  Y. Longval  S. Maestre  B. Maffei  J. Martignac  C. Marty  W. Marty  S. Masi  F. Mirc  R. Misawa  J. Montel  L. Montier  B. Mot  J. Narbonne  J-M. Nicot  F. Pajot  G. Parot  E. Pérot  J. Pimentao  G. Pisano  N. Ponthieu  I. Ristorcelli  L. Rodriguez  G. Roudil  M. Salatino  G. Savini  O. Simonella  M. Saccoccio  P. Tapie  J. Tauber  J.-P. Torre  C. Tucker 《Experimental Astronomy》2016,42(2):199-227

Future cosmology space missions will concentrate on measuring the polarization of the Cosmic Microwave Background, which potentially carries invaluable information about the earliest phases of the evolution of our universe. Such ambitious projects will ultimately be limited by the sensitivity of the instrument and by the accuracy at which polarized foreground emission from our own Galaxy can be subtracted out. We present the PILOT balloon project, which aims at characterizing one of these foreground sources, the polarized continuum emission by dust in the diffuse interstellar medium. The PILOT experiment also constitutes a test-bed for using multiplexed bolometer arrays for polarization measurements. This paper presents the instrument and its expected performances. Performance measured during ground calibrations of the instrument and in flight will be described in a forthcoming paper.  相似文献