A model for pore‐fluid‐sensitive rock behavior using a weathering state parameter     

R. J. Hickman  M. S. Gutierrez  V. De Gennaro  P. Delage 《国际地质力学数值与分析法杂志》2008,32(16):1927-1953

Chalk and other porous rocks are known to behave differently when saturated with different pore fluids. The behavior of these rocks varies with different pore fluids and additional deformation occurs when the pore fluid composition changes. In this article, we review the evidence that behavior in porous rocks is pore‐fluid‐dependent, present a constitutive model for pore‐fluid‐dependent porous rocks, and present a compilation of previously published data to develop quantitative relationships between various pore fluids and mechanical behavior. The model proposed here is based on a state parameter approach for weathering and has similarities to models previously proposed for weathering‐sensitive rocks in that the values for parameters that characterize material behavior vary as a function of weathering. Comparisons with published experimental data indicate that the model is capable of reproducing observed behavior of chalk under a variety of loading conditions and changes in pore fluid composition. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Formulation of a three‐dimensional rate‐dependent constitutive model for chalk and porous rocks     

R. J. Hickman  M. S. Gutierrez 《国际地质力学数值与分析法杂志》2007,31(4):583-605

Rate‐dependent behaviour of chalk and other porous rocks has undergone widespread study in geomechanics due to its implications on the performance of engineering structures. We present a rate‐dependent constitutive model for chalk and other porous rocks with several new features. The model formulation is based on a viscoplastic rate‐lines approach in which the axial strain rate depends on the proximity of the stress point to an elliptical reference surface. A non‐associated viscoplastic potential surface and an axial scaling algorithm are used to determine the viscoplastic strain components. The model predicts that axial yields stress varies as a power function of applied axial strain rate, as shown by published laboratory data. Comparisons with published experimental data indicate that the model is capable of reproducing observed rate‐dependent behaviour of chalk under a variety of loading conditions. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Comment on the postulate of three plane strain mechanisms     

Marte Gutierrez  Suzanne Lacasse 《国际地质力学数值与分析法杂志》1991,15(11):809-816

This note discusses the inconsistencies that are inherent in the postulate of three plane strain mechanisms. It is shown that this postulate violates the principle of invariance and one obtains different results depending on the choice of the reference axes. If formulated in the principal stress space, this postulate requires that the principal stress and principal plastic strain increment directions be coaxial. Constitutive models based on this postulate cannot be used for general loading situations involving principal stress rotation where significant non-coaxiality is obtained.  相似文献   

Ammonium Photoproduction from Aquatic Humic and Colloidal Matter     

Weiwei Wang  Matthew A. Tarr  Thomas S. Bianchi  Erika Engelhaupt 《Aquatic Geochemistry》2000,6(3):275-292

It has recently been shown thatnitrogen contained in humic substances can be releasedas low molecular weight species through photochemicalprocesses or reactions. Nitrogen released in thismanner may then become available for biological useand chemical reactivity. This report providesadditional kinetic data for nitrogen photochemistry oforganic matter in natural waters from Louisiana andfor Suwannee River humic and fulvic acids. Naturalwater samples were fractionated into colloidal(>0.2 m, <1000 Dalton) and dissolved (>1000Dalton) fractions and the kinetics of these fractionsas well as 0.2 m filtered water samples weremeasured. For irradiations of less than 10 hours ofsimulated noon-time sun, samples showed linearproduction of ammonium and first-order fading at350 nm. Ammonium photoproduction was enhanced asmuch as three-fold by lowering pH, but linear kineticswere maintained. Light-dark cycling showed continuedrelease of ammonium immediately after irradiation,followed by uptake at longer post irradiation times.A two step mechanism was proposed to explain theobserved kinetics. Calculated net daytime release ofammonium from natural surface waters ranged from 0.33to 1.9 M h^-1 in the samples studied,corresponding to a photic zone conversion rate of9–20% of the total organic nitrogen per day intoammonium.  相似文献   

The Effect of Fluid Content on the Mechanical Behaviour of Fractures in Chalk   总被引：7，自引：0，他引：7  

M. Gutierrez  L. E. Øino  K. Høeg 《Rock Mechanics and Rock Engineering》2000,33(2):93-117

Summary ?The paper presents an experimental study on the effects of fluid content on the mechanical behaviour of natural fractures in chalk. The aims of the study are to provide better understanding of the mechanisms of chalk-fluid interaction, in general, and to explain the behaviour of petroleum chalk reservoirs during water injection, in particular. The experiments were carried out on L?gerdorf chalk using the direct shear apparatus. Two types of fluids were used in the tests: 1) water, and 2) synthetic oil. L?gerdorf chalk is a water-wet material which will develop capillary pressures upon contact with water. Initially saturating the chalk with oil will enhance the water wettability by inducing additional capillary forces between water and the non-wetting oil. In addition to the tests on fractured chalk samples, unconfined compression and direct shear tests on intact chalk samples were performed. The results showed significant differences in the strength and deformation characteristics of intact chalk initially saturated with different fluids. Intact water-saturated chalk showed lower deformation modulus (about 50%) and lower peak (also about 50%) and residual shear strength than the oil-saturated chalk. Water injection in initially oil-saturated fractures resulted in significant normal deformation under constant effective normal stress and shear stress relaxation under fixed shear displacement. The water-induced deformation occurred almost instantaneously after only a few cm³ of water had been injected into the fracture, and further injection of water did not increase the water-induced deformation. After water injection, fractures in initially oil-saturated chalk showed significantly lower normal and shear stiffnesses and lower shear strength. The weakening in shear is attributed partly to the reduction in the basic friction angle, φ_b, and this reduction was verified in a series of tilt tests to measure the frictional resistance between smooth edges of core samples of chalk. The reduction in the basic friction angle implies that the interaction of chalk with water is governed not only by capillary forces, as postulated in several previous studies, but also by chemical and/or physio-chemical effects.  相似文献   

Inter-annual variability of precipitation over Southern Mexico and Central America and its relationship to sea surface temperature from a set of future projections from CMIP5 GCMs and RegCM4 CORDEX simulations     

Ramón Fuentes-Franco  Erika Coppola  Filippo Giorgi  Edgar G. Pavia  Gulilat Tefera Diro  Federico Graef 《Climate Dynamics》2015,45(1-2):425-440

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Sustainability aspects of thermal water production in the region of Hajdúszoboszló-Debrecen,Hungary     

Tamás Buday  Péter Szűcs  Miklós Kozák  Zoltán Püspöki  Richard William McIntosh  Erika Bódi  Béla Bálint  Kornél Bulátkó 《Environmental Earth Sciences》2015,74(12):7511-7521

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Present and future climatologies in the phase I CREMA experiment   总被引：1，自引：0，他引：1  

Erika Coppola  Filippo Giorgi  Francesca Raffaele  Ramon Fuentes-Franco  Graziano Giuliani  Marta LLopart-Pereira  Ashu Mamgain  Laura Mariotti  Gulilat Tefera Diro  Csaba Torma 《Climatic change》2014,125(1):23-38

We provide an overall assessment of the surface air temperature and precipitation present day (1976–2005) and future (2070–2099) ensemble climatologies in the Phase I CREMA experiment. This consists of simulations performed with different configurations (physics schemes) of the ICTP regional model RegCM4 over five CORDEX domains (Africa, Mediterranean, Central America, South America, South Asia), driven by different combinations of three global climate models (GCMs) and two greenhouse gas (GHG) representative concentration pathways (RCP8.5 and RCP4.5). The biases (1976–2005) in the driving and nested model ensembles compared to observations show a high degree of spatial variability and, when comparing GCMs and RegCM4, similar magnitudes and more similarity for precipitation than for temperature. The large scale patterns of change (2070–2099 minus 1976–2005) are broadly consistent across the GCM and RegCM4 ensembles and with previous analyses of GCM projections, indicating that the GCMs selected in the CREMA experiment are representative of the more general behavior of current GCMs. The RegCM4, however, shows a lower climate sensitivity (reduced warming) than the driving GCMs, especially when using the CLM land surface scheme. While the broad patterns of precipitation change are consistent across the GCM and RegCM4 ensembles, greater differences are found at sub-regional scales over the various domains, evidently tied to the representation of local processes. This paper serves to provide a reference view of the behavior of the CREMA ensemble, while more detailed and process-based analysis of individual domains is left to companion papers of this special issue.  相似文献   

运用生物地理学理论与遥感影像寻找本·拉登     

Thomas W. Gillespie  John A. Agnew  Erika Mariano  Scott Mossler  Nolan Jones  MattBraughton  Jorge Gonzalez 《遥感学报》2011,15(4):869-874

本·拉登到底在哪里？这是我们这个时代最重要的政治问题之一。在这篇文章中,我们依据反映生物分布和灭绝规律的生物地理学理论(距离衰减理论、岛屿生物地理理论、本·拉登个人数据),结合遥感数据(陆地卫星 ETM+、航天雷达地形测图、QuickBird),从全球、区域、局部三个空间尺度分析并最终指出本·拉登当前最可能的所在地。这是第一次运用科学手段来确定本·拉登居所。该方法具有可重复性：一旦美国情报部门提供新的信息,便可通过该方法重新定位本·拉登当前最有可能的藏身场所。  相似文献