Flow rule effects in the Tresca model

The Tresca failure criterion is used regularly in geotechnical engineering to compute the failure loads of clay soils deforming under undrained conditions. When this criterion is used together with the finite element method a plastic flow rule must also be incorporated in the elasto-plastic soil model.

The effects of the flow rule on the performance of a non-linear analysis using an elastic perfectly plastic soil model obeying the Tresca failure criteria are discussed in this note. Application of this model in a three-dimensional analysis causes computational difficulties, due to the gradient discontinuities that exist at the corner of the Tresca yield surface. Such discontinuities can be removed from the yield (or failure) surface using different methods. Two of the most widely used methods in removing singularities from the yield surface and their overall performances in a three-dimensional finite element analysis are discussed.

The motivation for this study comes from a concern raised by Randolph and Puzrin [Randolph MF and Puzrin AM Upper bound limit analysis of circular foundations on clay under general loading. Geotechnique, (2003);53(9):785–796, [5]] about reported instances of under predictions of the collapse loads by finite element analysis [Taiebat HA and Carter JP Numerical studies of the bearing capacity of shallow foundations on cohesive soil subjected to combined loading. Geotechnique, (2000);50(4):409–418, [7]] and [Taiebat HA and Carter JP Bearing capacity of strip and circular foundations on undrained clay subjected to eccentric loads. Geotechnique, (2002);52(1):61–64, [8]], [Gourvenec S and Randolph M Effect of strength non-homogeneity on the shape of failure envelopes for combined loading of strip and circular foundations on clay, Geotechnique, (2003);53(6):575–586, [4]], when it is usually expected that finite element results should overestimate the true collapse loads. The intent of this study is to demonstrate and reiterate that although the finite element method is an extremely powerful analytical tool for solution of engineering problems, it is nevertheless subjected to approximation errors due to simplifications that are necessarily made to prevent other numerical difficulties.     

Permeability of compacted granule–clay mixtures

Achieving a sufficiently low permeability for the aggregate-clay mixtures, whether used as the core of embankment dam or soil liner, is essential. The study illustrates the role of granule (bead or aggregate) content and size, confining stress and fabric anisotropy on the permeability of ceramic bead–lean clay and aggregate-fat clay mixtures. It is shown that depending on the plasticity of the clay, the permeability may decrease or increase with bead/aggregate content. The permeability also decreases when either granule size or confining stress increases. It is found that the permeability is affected by fabric anisotropy in such a manner that its value in the horizontal direction (k_h) is more than that in the vertical direction (k_v), however, k_h/k_v decreases towards 1 for bead contents equal to or below 40%. In high bead content mixtures (i.e., 60% beads) k_h/k_v reaches as high as 3 with an increase in the confining stress. The concept of the development of heterogeneous field of density in the clay is also used to demonstrate the impact of granule size and fabric anisotropy on the permeability.     

Classification and distribution of recent historic landslides in southern Nigeria

Recent historic landslides in southern Nigeria have been catalogued, classified and analysed in terms of their seasonal, geologic and topographic distributions.

It is found that 58% of the landslides fall within the complex^*

The distribution reveals that both sedimentary and non-sedimentary (igneous and metamorphic) terrains are vulnerable with the latter yielding a majority (73%) of the slide-debris flows. Implications of these distributions are discussed.     

“Giant pressure shadow” structure and ore-finding method of tectonic stress field in the Tongchang Cu-Au polymetallic orefield,Shaanxi, China: II. Dynamics of tectonic ore-forming processes and prognosis of concealed ores

John Ridley (1993) The relations between mean rock stress and fluid flow in the crust:With reference to vein-and lode-style gold deposit[J].Ore Deposit Reviews.8,23-37.

Kapper P.and Zeeh S.(2000) Relationship between fluid flow and faulting in the Alpine realm (Austria,Germany,Italy)[J].Sedimentary Geology.131,147-162.

Li Siguang (1976) Research Method of Geomechanics[M].Science Press,Beijing (in Chinese).

Liu Zhaochang,Li Fanyou,Zhong Kanghui,and Li Wei (1996) Tectonic Evolution and Metallogenesis on the Western Margin of the Yangtze Platform[M].pp.17-67.University of Electronics Science Press,Chengdu (in Chinese with English abstract).

Lu Guxian and Li Xiaobo (1996) Study on Tectonophysics and Tectonochemistry in Metallogeny[J].Journal of Geomechanics.2,38-40 (in Chinese).

Marc Polliand and Robert Moritz (1999) Basement-hosted quartz-barite sulfide veins in the French Alps:a record of Alpine tectonic fluid expulsion in external crystalline massifs-structural,fluid inclusion and isotopes (S and Sr) evidences[J].Economic Geology.94,37-56.

Minissale G.,Magro G.,Martinelli O.Vaselli,and Tassi G.F.(2000) fluid geochemical transect in the northern Apennines (central-northern Italy):Fluid genesis and migration and tectonic implications[J].Tectonophysics.319,199-222.

Shen Shumin,Zheng Fangfang,and Liu Wenying (1994) Three Dimensional Migration Potential Fields of the Tectonic Stress Driving and the Fluid Within Rocks[M].pp.37-42.Press of Earthquake,Beijing (in Chinese).

The institute of Chinese Irrigation and Electricity (1991) Notebook of Rock Mechanics[M].pp.25-29.Publishing House of Irrigation Works and Electric Power,Beijing (in Chinese).

Wang Dongbo (1991) Geochemistry of the South Qinling Au-Ag Ore Belt[M].pp.1-60.Central South University of Industry Press,Changsha (in Chinese with English abstract).

Wang Feng (1998) Concise Experimental Mechanics[M].Science Press,Beijing (in Chinese).

Wang Jiayin (1976) Discussion of Stress Minerals[M].Geological Publishing House,Beijing (in Chinese).

Wang Xiaofeng (1994) Flow in Rock and the Concentration and Dispersition of Elements[M].pp.119-131.Seismological Press,Beijing (in Chinese).

Yang Kaiqing (1986) Research subjects and orientation on the theory of tectono-genesis and tectono-metallogenesis[J] Bullentin of the Institute of Geomechanics.Geological Publishing House,Beijing.(7),1-10 (in Chinese with English abstract).

Yu Chongwen,Chen Kuang,Bao Zhengyu,and Chen Yaoting (1998) Dynamics of Hydrothermal Ore-forming Process[M].pp.1-6.Press of China University of Geoscience,Wuhan (in Chinese with English abstract).

Zhai Yusheng (1996) Questions of tectonics and fluid and ore-forming processes[J].Earth Science Frontes.23,230-236 (in Chinese with English abstract).

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Dissolution/precipitation kinetics of boehmite and gibbsite: Application of a pH-relaxation technique to study near-equilibrium rates

The dissolution and precipitation rates of boehmite, AlOOH, at 100.3 °C and limited precipitation kinetics of gibbsite, Al(OH)₃, at 50.0 °C were measured in neutral to basic solutions at 0.1 molal ionic strength (NaCl + NaOH + NaAl(OH)₄) near-equilibrium using a pH-jump technique with a hydrogen-electrode concentration cell. This approach allowed relatively rapid reactions to be studied from under- and over-saturation by continuous in situ pH monitoring after addition of basic or acidic titrant, respectively, to a pre-equilibrated, well-stirred suspension of the solid powder. The magnitude of each perturbation was kept small to maintain near-equilibrium conditions. For the case of boehmite, multiple pH-jumps at different starting pHs from over- and under-saturated solutions gave the same observed, first order rate constant consistent with the simple or elementary reaction: .

This relaxation technique allowed us to apply a steady-state approximation to the change in aluminum concentration within the overall principle of detailed balancing and gave a resulting mean rate constant, (2.2 ± 0.3) × 10⁻⁵ kg m⁻² s⁻¹, corresponding to a 1σ uncertainty of 15%, in good agreement with those obtained from the traditional approach of considering the rate of reaction as a function of saturation index. Using the more traditional treatment, all dissolution and precipitation data for boehmite at 100.3 °C were found to follow closely the simple rate expression:

R_net,boehmite=10^-5.485{m_OH^-}{1-exp(ΔG_r/RT)}, with R_net in units of mol m⁻² s⁻¹. This is consistent with Transition State Theory for a reversible elementary reaction that is first order in OH⁻ concentration involving a single critical activated complex. The relationship applies over the experimental ΔG_r range of 0.4–5.5 kJ mol⁻¹ for precipitation and −0.1 to −1.9 kJ mol⁻¹ for dissolution, and the pH_m ≡ −log(mH⁺) range of 6–9.6. The gibbsite precipitation data at 50 °C could also be treated adequately with the same model:R_net,gibbsite=10^-5.86{m_OH^-}{1-exp(ΔG_r/RT)}, over a more limited experimental range of ΔG_r (0.7–3.7 kJ mol⁻¹) and pH_m (8.2–9.7).     

Origin of micro-layering in a deep magma chamber: Evidence from two ultramafic–mafic layered xenoliths from Puy Beaunit (French Massif Central)

The origin of magmatic layering is still hotly debated. To try to shed some light on this problem, two ultramafic–mafic layered xenoliths from Puy Beaunit (French Massif Central) were investigated in detail. The nodules belong to a stratiform intrusion emplaced in the deep crust during the Permian (257 ± 6 Ma; Féménias, O., Coussaert, N., Bingen, B., Whitehouse, M., Mercier, J.-C., Demaiffe, D., 2003. A Permian underplating event in late- to post-orogenic tectonic setting. Evidence from the mafic–ultramafic layered xenoliths from Beaunit (French Massif Central). Chem. Geol. 199 293–315.). The 3 to 5 cm thick nodules have, in common, a central orthopyroxenite layer; the succession of layers is, respectively, norite–orthopyroxenite–norite (PBN 00-01) and norite–orthopyroxenite–harzburgite (PBN 00-03). The variations of both major (by electron microprobe) and trace, essentially the RE, elements (by LA-ICP-MS) were measured in major mineral phases (orthopyroxene, clinopyroxene, plagioclase, spinel) along cross-section perpendicular to the layering. Strong grain size, chemical and textural variations occur along these sections: they can be continuous or discontinuous, symmetrical or asymmetrical. Such complex variations cannot be solely related to a single magmatic history (fractional crystallisation, mineral sorting). Other processes such as element enrichment by residual liquid channelling along layer boundaries and/or sub-solidus recrystallisation and element redistribution must be invoked. It appears, in particular, that element distribution in the central orthopyroxenite layer could result from the injection of micro-sills of orthopyroxene-rich liquid between previously consolidated layers.     

Late Tremadoc and Early Floian Graptolites from Central Hunan, China

<正>Fourteen graptolite species of the Late Tremadoc and Early Floian are described from the Nanba section in the Yiyang area,Hunan Province.Among them,Paradelograptus onubensis, Kiaerograptus bulmani,K.kutchini and Paratemnograptus isolatus of the Late Tremadoc are first found in China.Based on the current graptolite materials,the correspondingly complete graptolite zones of Upper Tremadocian in China are recognized as follows(in ascending order):the Adelograptus tenellus Zone,the Aorograptus victoriae Zone,the Araneograptus murrayi Zone and the Hunnegraptus copiosus Zone.In the Nanba section,the Hunnegraptus copiosus Zone is overlain directly by the Tetragraptus approximatus Zone,there is no hiatus below the base of Floian.     

英文摘要

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英文摘要

APPLICATION OF WAVELET ANALYSIS FOR GEOPHYSICAL DATA AND COPPER MINERAL DEPOSITS FORECAST IN MANDAMAH AREA
SHEN Wei, FANG Cong-hui, CHANG Xing-guo （State Key Laboratory of Geo-Processes and Mineral Resources, Key Laboratory of Lithosphere Tectonics and Lithoprobing Technology of Ministry of Education, China University of Geosciences, Beijing 100083, China）. COMPUTING TECHNIQUES FOR GEOPHYSICAL AND GEOCHEMICAL EXPLORA- TION. 2009. 31 （6）： 0525     

英文摘要

Forward modeling is the base of inversion techniques, and the speed of forward modeling and how to store the coefficient matrix from inversion are the key techniques of the gravity and magnetic 3D inversion. An new Gravity and Magnetic 3D forward modeling method with rolling topography is presented in this paper. The principle is that two different scale matrixes with different measurements from forwarding modeling are produced based on the layers partition for inversion vertically, and the forward modeling values of the gravity and magnetic value with rolling topography are direcdy computed based on the local linear interpolating by taking the topography as the horizontal in the local model space.     

英文摘要

STUDY ON GRAVITY METHOD FOR DETECTING SUBSURFACE MASS;THE DYNAMIC RESPONSE OF SATURATED SANDSTONE BY CYCLIC LOADING;SOLUTION STRATEGIES FOR 2D AND 3D MAGNETOTELLURIC FORWARD MODELING BASED ON THE FINITE ELEMENT METHOD;A STABLE ALGORITHM FOR CALCULATING THE VERTICAL DERIVATIVES OF POTENTIAL FIELD;THE INSTANT DISPLAY FOUNCTION OF THE AIRBORNE ELECTROMAGNETIC PROFILE CURVE BASED ON SECONDARY DEVELOPMENT OF MAPGIS;     

Mineralogy and radioactivity of pegmatites from South Wadi Khuda area,Eastern Desert,Egypt

Stohl F.V.and Smith (1981) The Crystal Chemistry of the Uranyl Silicate Minerals[M].Department of Geosciences,the Pennsylvania State University,University Park.Pennsylvania.

Stuckless J.S.,Nkomo I.T.,Wenmer D.B.,and Van Trump G.(1984) Geochemistry and uranium favourability of the postorogenic granites of the north-eastern Arabian Shield,Kingdom of Saudi Arabia[J].Bull Fac.Earth Sci.King Abdel Aziz Univ.6,195-209.

William S.B.,Hanson S.L.,and Falster A.U.(2006) Samarskite-Yb:A new species of the samarskite group from the Little Patsy pegmatites,Jefferson County,Colorado[J].Canadian Mineralogist.44,1119-1125.

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2D INVERSION OF VES DATA UNDER ROLLING TOPOGRAPHY AND ITS APPLICATION
Considering to meet usually the rolling topogra- phy in the groundwater resource investigation, mineral exploration, engineering detection, etc. and based on the published literature in existence, this paper pres- ent our settlement of 2D inversion problem of VES da- m with the rolling topography by applying the total smooth constraint in the inversion. The approach can effectively process the FEM grid division and the in version software is made. Finally, it is proved that the inverted results is reliable through inverting the simulated and measured VES data, and the inversion software can be applied to the practical work.     

英文摘要

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Weiwoboidae fam.nov.of 'Higher' Fulgoroidea (Hemiptera:Fulgoromorpha) from the Eocene Deposits of Yunnan,China

<正>A new family of so-called‘higher' planthoppers,Weiwoboidae fam.nov.,from the Lower Eocene of Yunnan is described.A new monotypic genus,Weiwoboa gen.nov.,with Weiwoboa meridiana sp.nov.is also described and illustrated.The characters of tegmen venation of the new family,its evolution,and supposed relationships are briefly discussed.     

Seismic hazard analysis for critical infrastructures in California

California is in a highly seismically active region, and structures must be designed and constructed to withstand earthquakes. Seismic hazard analysis to estimate realistic earthquake ground motions and surface fault rupture offsets is done for various mitigation measures. The best policy is to avoid constructing structures crossing seismogenic faults. Because earthquake timings are unpredictable within our current understanding, the best method is time-invariant deterministic seismic hazard analysis (DHSA) to assess effects from the largest single earthquake called Maximum Credible Earthquake (MCEs) expected from seismogenic faults. Time-dependent hazard estimates such as those arrived at through probabilistic seismic hazard analysis (PSHA) are inherently unreliable. Hazard analyses based on MCEs have been in continuous use for the design and construction of highways and bridges in California for over 30 years.

This paper presents an alternative to other methods of analysis, e.g., Abrahamson (2000) [Abrahamson, N.A., 2000. State of the practice of seismic hazard evaluation. Melbourne: proceedings of GeoEng, 2000].     

Problems in the application of the SSHAC probability method for assessing earthquake hazards at Swiss nuclear power plants

From 2000 to 2004 a large scale probabilistic seismic hazard analysis (PEGASOS) was created and performed as a research project, sponsored by the Swiss NPP utilities to improve the assessment methodology for seismic risk in support of the plant-specific seismic PRAs. The project followed the methodology of the SSHAC [Senior Seismic Hazard Analysis Committee (SSHAC), 1997. Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts. NU-REG/CR-6372] procedures at its most elaborate way—level 4. Before practical implementation was to occur, a detailed review was performed including validation tests and analysis of uncertainty propagation. This paper presents the main results of the review. The review revealed that current PSHA (Probabilistic Seismic Hazard Analysis) methodology as based on logic trees, in conjunction with the SSHAC procedures, potentially leads to a significant overestimation of the seismic hazard in areas with low seismic activity due to the inherent possibilities of unconstrained accumulation of uncertainties. The preliminary results of the project did not pass any of our logical geological–scientific benchmark tests used in our attempts to perform a validation process of the PEGASOS analysis method. Some of the problems encountered are of generic nature and shall be studied carefully before making the decision of whether or not the Swiss nuclear power industry will adopt the recommended use of SSHAC-procedures as a basis for the evaluation of the seismic hazard for individual nuclear power plant seismic PRA without correction.     

Palaeogeographical implications of CretaceousBenthic Foraminifera recovered by the Deep Sea Drilling project in the Western South Atlantic ocean

Albian/Cenomanian benthic foraminiferal faunas recovered by the DSDP in the western South Atlantic Ocean (Leg 36) are described and analyzed from the palaeogeographic and palaeo-environmental points of view. In doing this the author compares Leg 36 assemblages in the western South Atlantic Ocean with coeval benthic foraminiferal faunas recovered in the eastern South Atlantic Ocean (Leg 40) and in the eastern Indian Ocean (Legs 26 and 27). The specific composition of these assemblages, except for Leg 27, is virtually the same. Consequently, they are considered to indicate the same depositional water depth at all relevant sites studied, whether located in the Angola Basin, the northern flank of the Walvis Ridge, the eastern margin of the Falkland Plateau or on the Naturaliste Plateau. All the assemblages indicate shallow environments around 100 m and not exceeding 300–400 m in the deepest parts, corresponding to the inner shelf and the inner part of the outer shelf. By contrast the foraminiferal associations of Leg 27 (especially Site 259) indicate a greater depth, of the order of 200–600 m (but not exceeding 1000 m) corresponding to upper slope of Sliter & Baker (1972) and Sliter (1972). These bathymetrical conclusions are in remarkable accord with those of Sliter (1976), based on planktic Foramini fera of Leg 36.Late Cretaceous (Campanian-Maastrichtian) material with benthic Foraminifera was limited to two positive samples; however, these faunas indicate much the same palaeo-environment as do the planktic ones analyzed by Sliter (1976).     

新疆哈密金窝子矿田逆冲推覆构造及其控矿作用

金窝子矿田控矿构造复杂,成矿条件独特,金矿化类型多样。经研究,金窝子矿田的形成与中天山地块向北山裂谷带逆冲推覆作用有关。逆冲推覆造就了金窝子矿田北、中、南3个不同性质的断裂带及不同的金矿化物理、化学环境,并分别控制了金矿田与其相关的金矿化类型及其成矿作用和金矿成矿系列。