A virtual surface concept for nested yield surface plasticity

A return mapping algorithm based on the concept of virtual surfaces is presented for stress integration in the numerical solution of boundary value problems using an elastoplastic multiple yield surface model. Both kinematic hardening and isotropic softening yield surfaces are addressed. With the implementation of virtual surfaces, the active yield surface is located before a stress update is implemented. The return mapping algorithm consists of only two steps. The first step consists of performing the intermediate update of the trial stress corresponding to the translation of all yield surfaces inside the active yield surface. Little calculation is involved in this step. The second step consists of performing the conventional explicit one-step radial return mapping of the updated trial stress on the corresponding active yield surface. The algorithm efficiency resides in the virtual surface based return mapping which preserves the elastic predictor representation of the updated trial stress, and limits iterations to at most two steps.     

A general basis for yield,failure and potential functions in plasticity

A new concept based on the use of a function expressed as a (complete) polynomial expansion in terms of the three invariants of the stress tensor is proposed for deriving yield, failure and plastic potential functions for use in plasticity based constitutive laws. A mathematical interpretation and physical meaning of the proposed concept are provided by using the idea of the singular nature of constiutive matrices in incremental hypoelastic laws. It is suggested that the proposed function and (polynomial) forms of material moduli can be synonymous. A number of specialized forms of the general function are adopted and their values at failure from advanced three-dimensional tests for a number of (geological) media are evaluated. The results indicate the possibility that there exist invariant numbers associated with the functions(s) that may apply to a wide range of materials. Some ideas on implementation of the proposed concept are also presented.     

A hierarchical single yield surface for frictional materials

This paper extends the formulation of a recent yield and failure criterion [Mortara G. A new yield and failure criterion for geomaterials. Géotechnique 2008;58(2):125–32] by modifying its shape in the deviatoric representation. Such a modification improves the performance of the surface introducing a constitutive parameter associated to the variation of the Lode angle. The criterion is validated through the comparison with experimental data obtained from multiaxial tests on soils, rocks and concrete. A special form of the criterion will be also derived for numerical applications in order to remove singularities of the previous criterion.     

基于C2阶连续函数的广义Hoek-Brown强度准则屈服面与塑性势面棱角圆化方法

Hoek-Brown强度准则的屈服面与塑性势面在棱角处导数无定义,具有数值奇异性,采用圆角进行光滑过渡只能满足一阶导数连续性,而二阶导数仍然无定义,使得棱边上一致切线模量矩阵无法正确计算,导致有限元总体平衡方程组Newton-Raphson隐式迭代二阶收敛性丧失。提出基于C2阶连续函数的广义Hoek-Brown准则屈服面与塑性势面棱角圆化方法,使得棱角处函数曲面二阶连续可导,棱边上一致切线模量矩阵可精确计算。基于ABAQUS数值开发平台,采用FORTRAN语言编制Hoek-Brown准则理想弹塑性UMAT用户子程序,通过数值算例验证所提方法的正确性。     

Peritidal carbonate facies models: A review

Existing facies models for peritidal carbonates are limited in number and do not reflect the wide spectrum of possible types. The major depositional processes in peritidal carbonate environments are reviewed in order to stress the complex nature of the systems. The tidal channel model is critically discussed and it is suggested that channel deposits may be of minor importance in typical shoaling-up sequences. The possible causes of multiple asymmetrical sequences are reviewed.     

月面环境与月壤特性研究的主要问题探讨

月面环境与月壤特性是月球探测和月球科学研究的重要基础,对它们的研究一直在不断加深,本文对月球表面地形地貌、热环境以及月壤特性三个方面的研究现状进行了总结,初步分析了这三个方面研究目前存在的一些主要问题：（1）地形地貌对月球定量遥感的影响以及南极艾特肯（SPA）盆地等地貌单元的年代学划分和成因演化;（2）月面热辐射、月表物理温度和热流等月面热环境特征的进一步探测和全面分析,以及其对地球反照率变化的响应;（3）月壤形成演化过程及空间风化作用,月球极区氢富集机制和水冰探测,以及月球资源开发利用。     

A unified approach to the implicit integration of standard,non‐standard and viscous plasticity models

It is shown how modern concepts to integrate the elasto‐plastic rate equations of standard plasticity via an implicit algorithm can be generalized to plasticity without an explicitly defined yield surface and to overstress‐type models of viscoplasticity, where the stress point can be located outside the loading surface. For completeness, a tangent operator is derived that is consistent with the update algorithm. Copyright © 2002 John Wiley & Sons, Ltd.     

Si stable isotopes in the Earth's surface: A review

Silicon (Si) is the second most abundant element on Earth after oxygen. Only few studies have attempted to use stable isotopes of Si as proxies for understanding the Si cycle and its variations in the past. By using three different methods (IRMS, MC–ICP–MS and SIMS), the overall measurements show that the isotopic composition (δ³⁰Si) of terrestrial samples ranges from − 5.7‰ to + 3.4‰. Dissolved Si in rivers and seawater is ³⁰Si-enriched (− 0.8‰ < δ³⁰Si < + 3.4‰) compared to Si in endogeneous rocks (− 1.1‰ < δ³⁰Si < + 0.7‰). This global enrichment is counterbalanced by the Si-bearing phases (biogenic silica, clays, quartz) where Si is, in average, ³⁰Si-depleted (− 5.7‰ < δ³⁰Si < + 2.6‰). These values are the result of fractionation which have been measured or estimated from − 0.3‰ to − 3.8‰. The fractionation is modeled by two types of approaches: the Rayleigh distillation model (closed system) and the steady-state model (open system). These models have been used in the most recent studies to explain the observed δ³⁰Si variations in continental environments and in the sub-Antarctic Ocean.     

Discussion: The Hawkesbury Sandstone: A critical review of proposed environmental models

A critical evaluation of conflicting hypotheses for the deposition of the Hawkes‐bury Sandstone suggests that the Barrier Island‐Tidal Delta Model of Conolly (1969) is preferable to the Low Sinuosity River (Brahmaputra) Model of Conaghan & Jones (1975).     

Active fire monitoring and fire danger potential detection from space: A review

Wildland fire is both one of the major natural hazards and a natural process for ecosystem persistence. Accurate assessment of fire danger potential and timely detection of active fires are critical for fire fighting and fuel management. Space-borne measurements have become the primary approaches for these efforts. Many research works have been conducted and some data products have been generated for practical applications. This paper presents a review of the major sensors and algorithms for active fire monitoring and fire danger potential detection from space. Major sensors and their characteristics, physical principles of the major algorithms are summarized. Limitations of these algorithms and future improvements are also discussed.     

Delamerian Orogeny and potential foreland sedimentation: A review of age and stratigraphic constraints

A review of available geochronology and biostratigraphy leads to the conclusion that a considerable thickness of Cambrian sedimentary rocks exposed in the Arrowie and Stansbury Basins, South Australia, was probably deposited in a foreland setting during early phases of the Delamerian Orogeny. In contrast to most previous stratigraphic correlation schemes, we consider that the pre‐tectonic Kanmantoo Group was deposited synchronously with the locally thick upper Hawker Group in essentially en echelon basins during a final phase of extensional sedimentation within the Adelaide ‘Geosyncline’. The base of the locally overlying ‘redbed package’ (base of the Billy Creek and Minlaton Formations) is interpreted as the sedimentological signature of the onset of convergent deformation and associated uplift within the Delamerian Orogen at about 522 Ma. This early ('Kangarooian') phase of the Delamerian Orogeny is interpreted as the progressive development of a coherent sigmoidal fold‐thrust belt within the combined Fleurieu‐Nackara Arcs, with locally developed high‐temperature‐low‐pressure metamorphism and granitoid intrusions dating from about 516 Ma. The ‘redbed package’ is absent from the Fleurieu‐Nackara Arc region and displays isopach, palaeocurrent and facies trends consistent with derivation from this uplifted area or from the associated flexural bulge to the west. From seismic evidence we conclude that thick foreland basin deposits are present beneath Gulf St Vincent. Late phases of the Delamerian Orogeny led to local and relatively mild deformation of the early foreland deposits.     

浙江南部近海沉积物柱状样中脂类生物标志物的组成及形态分布

湖泊沉积物中直链脂肪族化合物(MCCs)对气候变化响应敏感,环境条件的变化可促使MCCs在游离态和结合态间发生转化,是古气候重建的重要生物标志物。以往研究中对样品前处理通常采用混合溶剂提取法得到MCCs游离态组分,而以化学键合、物理吸附等形式赋存的结合态组分无法通过溶剂提取,不能获取结合态组分特征对气候环境变化的指示信息。本文将热裂解这一有机质高效分解技术与气相色谱-质谱(GC-MS)联用,实现了对内蒙古伊和沙日乌苏湖泊沉积物有机质组成的精细刻画,并识别、分析了共计3类、71项结合态MCCs化合物。结果表明：热解温度是影响热裂解-气相色谱-质谱(Py-GC/MS)分析沉积物样品中结合态MCCs分布特征的主要因素,450℃以下热解能量较低导致结合态MCCs解析不充分,550℃和650℃下各类结合态MCCs(含正构烷烃、正构烯烃及α-正构脂肪酮)充分解析,可经GC-MS实现在线分离、识别;随着热解温度升高,裂解产物中MCCs平均链长趋于降低,过高的裂解能量影响了产物中MCCs化合物链长特征对气候变化指示的敏感性。经研究各类MCCs分布特征发现,550℃下正构烷烃平均链长特征与传统气候替代指标游离态正构烷烃单体碳同位素δ¹³C_27~33具有较好的相关性(R=0.83)。结合态正构烷烃ACL_25~31指标响应了区域有效降水变化特征,识别了区域内5.6ka、3.9ka前后的干旱期,反映了东亚夏季风强度变化,对应了北半球中纬度有效降水变化。

     

地表稠油污染物地球化学研究现状

关于石油轻组分对环境的污染问题相对研究较多，而针对稠油污染物的研究则较薄弱。本文着重介绍了目前地表稠油污染物的研究进展，涉及稠油污染的潜在严重性和危害性，其赋存形态、迁移方式和演化机制，以及目前常用的修复方法。进一步开展稠油污染物在地表土壤以及水体中的地球化学特征及演化机制方面的研究工作，将有助于为稠油开采和炼制地区的环境保护和修复治理提供更多的科学依据。     

Satellite remote sensing applications for surface soil moisture monitoring: A review

Surface soil moisture is one of the crucial variables in hydrological processes, which influences the exchange of water and energy fluxes at the land surface/atmosphere interface. Accurate estimate of the spatial and temporal variations of soil moisture is critical for numerous environmental studies. Recent technological advances in satellite remote sensing have shown that soil moisture can be measured by a variety of remote sensing techniques, each with its own strengths and weaknesses. This paper presents a comprehensive review of the progress in remote sensing of soil moisture, with focus on technique approaches for soil moisture estimation from optical, thermal, passive microwave, and active microwave measurements. The physical principles and the status of current retrieval methods are summarized. Limitations existing in current soil moisture estimation algorithms and key issues that have to be addressed in the near future are also discussed.     

Uranyl adsorption and surface speciation at the imogolite-water interface: Self-consistent spectroscopic and surface complexation models

Macro- and molecular-scale knowledge of uranyl (U(VI)) partitioning reactions with soil/sediment mineral components is important in predicting U(VI) transport processes in the vadose zone and aquifers. In this study, U(VI) reactivity and surface speciation on a poorly crystalline aluminosilicate mineral, synthetic imogolite, were investigated using batch adsorption experiments, X-ray absorption spectroscopy (XAS), and surface complexation modeling. U(VI) uptake on imogolite surfaces was greatest at pH ∼7-8 (I = 0.1 M NaNO₃ solution, suspension density = 0.4 g/L [U(VI)]_i = 0.01-30 μM, equilibration with air). Uranyl uptake decreased with increasing sodium nitrate concentration in the range from 0.02 to 0.5 M. XAS analyses show that two U(VI) inner-sphere (bidentate mononuclear coordination on outer-wall aluminol groups) and one outer-sphere surface species are present on the imogolite surface, and the distribution of the surface species is pH dependent. At pH 8.8, bis-carbonato inner-sphere and tris-carbonato outer-sphere surface species are present. At pH 7, bis- and non-carbonato inner-sphere surface species co-exist, and the fraction of bis-carbonato species increases slightly with increasing I (0.1-0.5 M). At pH 5.3, U(VI) non-carbonato bidentate mononuclear surface species predominate (69%). A triple layer surface complexation model was developed with surface species that are consistent with the XAS analyses and macroscopic adsorption data. The proton stoichiometry of surface reactions was determined from both the pH dependence of U(VI) adsorption data in pH regions of surface species predominance and from bond-valence calculations. The bis-carbonato species required a distribution of surface charge between the surface and β charge planes in order to be consistent with both the spectroscopic and macroscopic adsorption data. This research indicates that U(VI)-carbonato ternary species on poorly crystalline aluminosilicate mineral surfaces may be important in controlling U(VI) mobility in low-temperature geochemical environments over a wide pH range (∼5-9), even at the partial pressure of carbon dioxide of ambient air (p_CO2 = 10^−3.45 atm).     

土蠕变性质及其模型研究综述与讨论

对土的蠕变性质及其本构模型研究进行了系统地总结,主要内容包括：时间和应力对土蠕变性质的影响、土蠕变破坏准则、蠕变势和塑性势关系、蠕变微观机制、宏观和微观本构模型等。此外,基于上述总结,提出了土等效变形过程的概念,探讨了土蠕变模型中时间效应的表述方式,提出了一种可加快土蠕变试验的方法。     

ISA model: A constitutive model for soils with yield surface in the intergranular strain space

In this article, a new constitutive model for soils is proposed. It is formulated by means of plasticity, but in contrast to the precedent works, it presents a yield function describing a surface within the intergranular strain space. This latter is a state variable providing information of the recent strain history. An expression for the plastic strain rate has been proposed to guarantee the stress rate continuity. Under the application of medium or large strain amplitudes, the constitutive equation becomes independent of the intergranular strain and delivers a mathematical structure similar to some Karlsruhe hypoplastic models. Some simulations of monotonic and cyclic triaxial test are provided to evaluate and analyze the model performance. Copyright © 2015 John Wiley & Sons, Ltd.     

Thallium: A potential guide to mineral deposits

Several recent studies have suggested that rocks associated with mineral deposits of hydrothermal origin are generally enriched in Rb. TI is similar in its geochemical characteristics to Rb, but its use as a potential guide to ore deposits has not been suggested. Although TI has the same size and valency as Rb, it is concentrated more in residual melts than Rb and K because the TI-O bond is more covalent and weaker than either the Rb-O or K-O bonds.A new method which is rapid and precise has been developed by one of the authors for the determination of TI in geological materials at the ppb level. About 350 rocks from 4 mineralized areas in northeastern Washington and central Montana were analyzed for TI by this method. Most of these rocks were also analyzed for SiO₂, A1₂O₃,Fe₂O₃, MgO, CaO, Na₂O, K₂O, TiO₂, P₂O₅, MnO, Ag, As, Au, Ba, Co, Cu, F, Li, Mo, Ni, Pb, Sr, Sb, Sn, Sr, Te, U, W, and Zn. The ore deposits of the areas studied include the gold-silver deposits of the Republic district, the uranium deposit of the Midnite mine, the coppermolybdenum deposit of Mount Tolman, and the gold deposits of the North Moccasin mining district.In all the mineralized areas there is significantly more TI in hydrothermally altered rocks than in unaltered rocks. The very high abundance of TI in the altered rocks of the North Moccasin gold district, and the significant positive correlations of TI and K and TI and Rb in the mineralized rocks of the other three areas suggest that TI was concentrated in hydrothermal fluids. In altered rocks the average K/Rb and K/TI ratios are lower, and the Rb/Sr and TI/Sr ratios are higher.Often the abundance of TI and the K/TI and TI/Sr ratios are more useful in delineating mineralized areas than the abundance of Rb and the K/Rb and Rb/Sr ratios. The ternary relationships between TI and several other elements, especially Rb, K, Ba, and Sr, show mineralized rocks to fall near the TI apices or near the TI-Rb or TI-K boundaries.