Numerical investigation of alternative fracture stiffness measures and their respective scaling behaviours          下载免费PDF全文

Joseph P. Morris  Jeroen Jocker  Romain Prioul 《Geophysical Prospecting》2017,65(3):791-807

We study the mechanical deformation of fractures under normal stress, via tangent and specific fracture stiffnesses, for different length scales using numerical simulations and analytical insights. First, we revisit an equivalent elastic layer model that leads to two expressions: the tangent stiffness is the sum of an “intrinsic” stiffness and the normal stress, and the specific stiffness is the tangent stiffness divided by the fracture aperture at current stress. Second, we simulate the deformation of rough fractures using a boundary element method where fracture surfaces represented by elastic asperities on an elastic half‐space follow a self‐affine distribution. A large number of statistically identical “parent” fractures are generated, from which sub‐fractures of smaller dimensions are extracted. The self‐affine distribution implies that the stress‐free fracture aperture increases with fracture length with a power law in agreement with the chosen Hurst exponent. All simulated fractures exhibit an increase in the specific stiffness with stress and an average decrease with increase in length consistent with field observations. The simulated specific and tangent stiffnesses are well described by the equivalent layer model provided the “intrinsic” stiffness slightly decreases with fracture length following a power law. By combining numerical simulations and the analytical model, the effect of scale and stress on fracture stiffness measures can be easily separated using the concept of “intrinsic” stiffness. We learn that the primary reason for the variability in specific stiffness with length comes from the fact that the typical aperture of the self‐affine fractures itself scales with the length of the fractures.  相似文献   

Stepwise palaeoclimate change across the Eocene–Oligocene transition recorded in continental NW Europe by mineralogical assemblages and δ15Norg (Rennes Basin,France)          下载免费PDF全文

Romain Tramoy  Marie Salpin  Johann Schnyder  Alain Person  Mathieu Sebilo  Johan Yans  Véronique Vaury  Jérôme Fozzani  Hugues Bauer 《地学学报》2016,28(3):212-220

The Eocene–Oligocene transition (EOT, ~34 Ma) is the largest global cooling of the Cenozoic Era and led the Earth's climatic system to change from a greenhouse to an icehouse mode. Although it is well documented in marine settings, the few studies focusing on continental environments have demonstrated regional heterogeneities. The study core CDB1, located in the Rennes Basin (Western France), is a unique terrestrial (lacustrine–palustrine) record comprising well‐preserved and terrestrial‐derived organic‐rich sediments encompassing the EOT. Clay minerals and the first organic nitrogen isotope record (δ¹⁵N_org) of terrestrial origin for this period are used to reconstruct palaeoclimate changes across this key interval. As suggested in worldwide marine and a few continental records, a stepwise transition from warm/humid conditions in the Late Eocene to cooler/drier conditions in the Early Oligocene is confirmed in the area. In addition, an episode of drier conditions in the Late Eocene and humid/dry cycles in the Early Oligocene are suggested.  相似文献   

Scratch hardness–strength solutions for cohesive‐frictional materials     

Romain Bard  Franz‐Josef Ulm 《国际地质力学数值与分析法杂志》2012,36(3):307-326

In this paper we develop analytical solutions for scratch hardness–strength relations for cohesive‐frictional materials of the Mohr–Coulomb and Drucker–Prager type. Based on the lower bound yield design approach, closed‐form solutions are derived for frictionless scratch devices, and validated against computational upper bound and elastoplastic finite element solutions. The influence of friction at the blade–material interface is also investigated, for which a simple computational optimization is proposed. Illustrated for scratch tests on cement paste, we show that the proposed solutions provide a convenient way to determine estimates of cohesion and friction parameters from scratch data, and may serve as a benchmark to identify the relevance of strength models for scratch test analysis. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Travel time to a well pumping an unconfined aquifer without recharge     

Chapuis RP  Chesnaux R 《Ground water》2006,44(4):600-603

A solution is given for the travel time to a well pumping an ideal, horizontal unconfined aquifer, under steady-state conditions, when recharge from infiltration is negligible. Three forms of the solution are provided: a closed-form solution, an integral to be calculated in a worksheet, and a simple equation. The three forms of the solution give travel times nearly identical to those obtained using a finite-element code for saturated and unsaturated flow and particle tracking.  相似文献   

Accurate and High‐Precision Determination of Boron Isotopic Ratios at Low Concentration by MC‐ICP‐MS (Neptune)     

Catherine Guerrot  Romain Millot  Michèle Robert  Philippe Négrel 《Geostandards and Geoanalytical Research》2011,35(2):275-284

We report an approach for the accurate and reproducible measurement of boron isotope ratios in natural waters using an MC‐ICP‐MS (Neptune) after wet chemistry sample purification. The sample matrix can induce a drastic shift in the isotopic ratio by changing the mass bias. It is shown that, if no purification is carried out, the direct measurement of a seawater diluted one hundred times will induce an offset of ?7‰ in the isotopic ratio, and that, for the same concentration, the greater the atomic mass of the matrix element, the greater the bias induced. Whatever the sample, it is thus necessary to remove the matrix. We propose a method adapted to water samples allowing purification of 100 ng of boron with a direct recovery of boron in 2 ml of 3% v/v HNO₃, which was our working solution. Boron from the International Atomic Energy Agency IAEA‐B1 seawater reference material and from the two groundwater reference materials IAEA‐B2 and IAEA‐B3, was chemically purified, as well as boron from the certified reference material NIST SRM 951 as a test. The reproducibility of the whole procedure (wet chemistry and MC‐ICP‐MS measurement) was ± 0.4‰ (2s). Accuracy was verified by comparison with positive‐TIMS values and with recommended values. Seawater, being homogeneous for boron isotope ratios, is presently the only natural water material that is commonly analysed for testing accuracy worldwide. We propose that the three IAEA natural waters could be used as reference samples for boron isotopes, allowing a better knowledge of their isotopic ratios, thus contributing to the certification of methods and improving the quality of the boron isotopic ratio measurements for all laboratories.  相似文献   

The Valais units in Savoy (France): a key area for understanding the palaeogeography and the tectonic evolution of the Western Alps     

Andrea Loprieno  Romain Bousquet  Stefan Bucher  Stefano Ceriani  Florian H. Dalla Torre  Bernhard Fügenschuh  Stefan M. Schmid 《International Journal of Earth Sciences》2011,100(5):963-992

The Valais units in Savoy (Zone des Brèches de Tarentaise) have been re-mapped in great detail and are subject of combined stratigraphic, structural and petrological investigations summarized in this contribution. The sediments and rare relics of basement, together with Cretaceous age mafic and ultramafic rocks of the Valais palaeogeographical domain, represent the heavily deformed relics of the former distal European margin (External Valais units) and an ocean–continent transition (Internal Valais unit or Versoyen unit) that formed during rifting. This rifting led to the opening of the Valais ocean, a northern branch of the Alpine Tethys. Post-rift sediments referred to as “Valais trilogy” stratigraphically overlie both External and Internal Valais successions above an angular unconformity formed in Barremian to Aptian times, providing robust evidence for the timing of the opening of the Valais ocean. The Valais units in Savoy are part of a second and more external mid-Eocene high-pressure belt in the Alps that sutured the Briançonnais microcontinent to Europe. Top-N D1-deformation led to the formation of a nappe stack that emplaced the largely eclogite-facies Internal Valais unit (Versoyen) onto blueschist-facies External Valais units. The latter originally consisted of, from internal to external, the Petit St. Bernard unit, the Roc de l’Enfer unit, the Moûtiers unit and the Quermoz unit. Ongoing top-N D2-thrusting and folding substantially modified this nappe stack. Post 35 Ma D3 folding led to relatively minor modifications of the nappe stack within the Valais units but was associated with substantial top-WNW thrusting of the Valais units over the Dauphinois units along the Roselend thrust during W-directed indentation of the Adria block contributing to the formation of the arc of the Western Alps.  相似文献   

Protected areas in mainland Southeast Asia, 1973–2005: Continuing trends     

Steve Déry  Romain Vanhooren 《Singapore journal of tropical geography》2011,32(2):185-202

Since the 1970s, protected area networks in mainland Southeast Asian countries have developed significantly to occupy 4–25 per cent of their respective national areas, located mostly in the mountainous domains of ethnic minority peoples. Through this process, regions that were only nominally part of national geobodies until the 1950s have become more territorially integrated. The complexity of the characteristics and geographical impacts of this territorialisation have yet to be grasped. As a step in this direction, we briefly outline a multilevel systems approach that usefully contextualizes these issues together with a historical and cartographical assessment of the evolution of protected area networks for Burma, Thailand, Laos, Cambodia and Vietnam. Our main findings are intertwined. On the one hand, protected areas represent a new tool of state intervention in mountainous areas, clearly in keeping with past, notably colonial, actions. On the other hand, this evolution in state territorialisation and attendant power relations have disrupted, far more deeply than previous actions, the pre‐1970s sociogeographical organization in mountainous areas, where most of the region's residual forests remain.  相似文献   

Significance of the clay mineral distribution in fluvial sediments of the Neogene to Recent Himalayan Foreland Basin (west‐central Nepal)     

Pascale Huyghe  Romain Guilbaud  Matthias Bernet  Albert Galy  Ananta Prasad Gajurel 《Basin Research》2011,23(3):332-345

Clay mineral assemblages of the Neogene Himalayan foreland basin are studied to decipher their significance with respect to tectonic and climate processes. Fluvial deposits of the Siwalik Group (west‐central Nepal), and sediment of the Ganga River drainage system were analysed for clay mineralogy. The observed clay mineral assemblages are mainly composed of illite (dominant), chlorite, smectite and kaolinite. Illite and chlorite are chiefly of detrital origin, derived from Himalayan sources. Kaolinite and smectite are authigenic, and mainly developed within pore space and as coating of detrital particles. With increasing burial, diagenetic processes affected the original clay mineral signature. Illitisation of smectite and kaolinite occurred below 2500 and 3500 m depth, respectively. Therefore, illite in the lower parts of the Siwalik Group consists of a mixture of inherited illite and illitised smectite and kaolinite, as suggested by illite crystallinity. Detrital grains that make up the framework of the Siwalik Group sandstones mainly consist of quartz, feldspar and lithic fragments, which are principally of sedimentary and metamorphic origin. Lithoclast content increases over time at the expense of quartz and K‐feldspar in response to uplift and erosion of the Lesser Himalaya Series since about 11–10 Ma. Despite mainly felsic source rocks, dominantly physical erosion processes in the Himalayan belt, and high‐energy fluvial depositional systems, smectite is abundant in the <7 Ma Siwalik Group deposits. Analyses of the Siwalik deposits and comparison with the clay mineralogy of the modern drainage system suggest that smectite preferentially formed in floodplains and intermontane valleys during early diagenesis because of downward percolating fluids rich in cations from weathering and soil development. In general, increasing seasonality and aridity linked to variability of the Asian monsoon from about 8 Ma enhanced clay mineral formation and development of authigenic smectite in paleo‐plains on the southern side of the Himalaya.  相似文献   

Fundamental differences between SPH and grid methods   总被引：1，自引：0，他引：1  

Oscar Agertz  Ben Moore  Joachim Stadel  Doug Potter  Francesco Miniati  Justin Read  Lucio Mayer  Artur Gawryszczak  rey Kravtsov  Åke Nordlund  Frazer Pearce  Vicent Quilis  Douglas Rudd  Volker Springel  James Stone  Elizabeth Tasker  Romain Teyssier  James Wadsley  Rolf Walder 《Monthly notices of the Royal Astronomical Society》2007,380(3):963-978

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Search for New Interesting Objects in the Second Part of the FBS     

A. M. Mickaelian  H. V. Abrahamian  J. Guibert  R. Chesnel 《Astrophysics》2002,45(1):73-78

We present the results of a study of the FBS blue stellar objects with the goal of discovering new interesting objects. Forty-seven FBS objects have been observed with the Byurakan Observatory 2.6m telescope in 1987-1991 and scanned with the MAMA scanning machine at Observatoire de Paris in 1997-1999. 5 QSOs/Sy1s, 4 emission-line stars, five white dwarfs, and a number of continuous spectra objects (possible BL Lacs and DC white dwarfs) have been revealed.  相似文献