Gibson大变形固结理论的一种连续介质力学表述

为了克服Gibson大变形固结理论的一维局限性,提出了一个新的连续介质力学模型,其中,采用第2类Piola- Kirchhoff应力和Green应变分别替代Lagrange应力和孔隙比。该模型可以考虑土体压缩性和渗透性的非线性变化以及几何非线性,并具有易于推广到多维模型的优势。结合试验资料,探讨了新模型的固结系数和对流系数的变化规律,结果表明,对流系数随着应变增加而减小,反映了大变形固结过程中土体自重效应在不断减弱。     

大变形固结理论最终沉降量分析

大变形理论的力学机制较为严格,但由于其固有的复杂性和非线性,目前对大小变形理论计算的沉降量差别仍存在争议。基于连续介质力学基本原理,采用土力学符号约定推导了T.L.描述的大变形固结增量有限元方程组及其总应力分析形式。结合算例,分析了材料线性化和材料几何双线性化简化算法的影响,探讨了较合适的荷载增量步长,讨论了大、小变形法计算的最终沉降量差别。结果表明,荷载增量步长对两种线性化法计算结果较为敏感;大变形法计算的沉降量偏大于小变形结果,这可能是由几何非线性问题的“拉压刚度不同”效应引起;初应力矩阵对最终沉降量有较大影响等。     

一维大变形主、次固结耦合新模型

针对传统一维大变形固结理论不能考虑土体次固结变形的缺点,在连续介质力学有限变形理论和土力学固结理论基础上,提出了全新的一维大变形主、次固结耦合模型。该模型采用超静孔压为控制变量,可以分别表述为欧拉坐标、拉格朗日坐标和固相体积坐标等三种形式,其中均可以显式地反映出土体重度变化、固相速度、地表沉降速度、地下水位变化、荷载变化和次固结等6个因素的影响。在不同简化条件下,新模型可以分别退化为以往学者提出的相关模型。当不考虑次固结效应时,新模型与经典的Gibson大变形固结模型完全等价。从便于工程应用的角度而言,新模型中仅考虑次固结和外荷载变化的退化形式更便于求解,可作为一种供参考的实用模型。     

Contemporaneous development of mullions and hornblende lineations in divergent directions

A mullion structure is described from a several meter thick amphibolite from the Precambrian bedrock of south-eastern Norway. The mullion axes deviate about 60–70⁰ from the fold axis defined in the amphibolite by the constructed intersection of foliation planes. The fold axis is also reflected in the lineated hornblende grains. The orientation of the mullion axes is parallel to the trace of the amphibolite foliation on the mullioned surface. It is concluded that the mullions were formed on a discordant surface (probably a fracture surface) in responce to movement along the intersecting foliation planes at the same time as the hornblende lineation was developed.

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Zusammenfassung Aus dem südostnorwegischen präkambrischen Grundgebirge wird aus einem mehrere Meter mächtigen verfalteten Amphibolit eine Mullion-Struktur beschrieben. Die Achsen der Mullions weichen 60–70⁰ von der Faltenachse ab, welche aufgrund der Biotitfoliationen im Amphibolit konstruiert werden konnte. Diese Faltenachse wird auch von den linearen Hornblenden nachgezeichnet. Es wird angenommen, daß sich die Mullions auf einer diskordanten Fläche (wahrscheinlich einer Bruchfläche) gebildet haben. Auf dieser Fläche verlaufen die Mullion-Achsen parallel der Spur der Amphibolit-Foliation. Die Mullions entstanden gleichzeitig mit den linearen Hornblenden infolge einer Bewegung entlang der sich schneidenden Foliationsebenen.

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Résumé Une structure en «mullion» a été étudiée dans des amphibolites, d'âge Précambrien, en Norvège. Les mullions proviennent d'une couche discordante, qui a été déformée avec les amphibolites. On observe que les axes des mullions font une angle de 60 à 70 degré avec la linéation (prismes de hornblende) qui est parallèle aux axes des plis; les axes des mullions et la linéation sont situés dans le plan de la foliation des amphibolites.

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Mullion-Struktur - . 60–70 , . . , (, ). . .

     

Strain distribution in superposed buckling folds and the problem of reorientation of early lineations

Two series of experiments were carried out with soft model-materials in order to assess the relative importance of initial homogeneous strain, external rotation and late-stage strain in reorienting early lineations during superposed buckle-folding. In the first series cylindrical buckling folds were produced in embedded planar sheets containing a “lineation”. In the second series noncylindrical folds were produced by compression of a set of cylindrical folds. The experiments indicate that the ratio of buckle shortening to layer-parallel strain is much smaller when the principal extension is parallel to the fold-axis than in the case when the principal extension is perpendicular to the fold-axis. In very competent rocks, the reorientation of old lineations is mainly by external rotation and by the associated concentric longitudinal strain. In moderately competent rocks, the orientation of early lineations always changes by initial homogeneous strain before buckling becomes significant. Because of the unlike amounts of initial strain in layers of different competences, orientations of unrolled lineations may not be parallel in disharmonically folded layers of unlike competences. Under certain conditions the early lineation may become virtually parallel to the later fold-axis. The experiments indicate that the effects of late-stage strain in buckle-folding are largely restricted to the incompetent layers of a multilayer. Hence, if orientation data of early lineations in both competent and incompetent rocks are lumped together, the pattern of orientation may become quite complex. Even for a single competent layer, the pattern of early lineations can locally become complex because of the complex nature of concentric longitudinal strain (and strain resulting from stretching of middle surface of the layer), development of conical folds, development of shear strain along hinge zones of deformed early folds and also because of the development of different orders of folds in both the first and the second deformations.     

Patterns of deformed early lineations over later folds formed by buckling and flattening

The patterns of deformed early lineations (L₁) over later folds (F₂) can be classified into several morphological types depending on the nature of variation of L₁ F₂ over the folds. The field relations indicate that the folds under consideration are neither shear folds nor parallel folds modified by flattening. The lineation patterns are therefore interpreted in terms of an empirical model of simultaneous buckling and flattening in which it is assumed that (i) the central surface of the folded layer remains a sine curve in transverse profile, (ii) the ratio of rates of buckle shortening to homogeneous strain is proportional to sin 2a, with a as the dip angle and (iii) the progressive deformation is coaxial with the Z-axis of bulk strain parallel to the planar segments of the early folds. The model gives an insight into the relative importance of different physical factors which control the development of dissimilar lineation patterns. Not all lineation patterns are explicable by this simplified model. Thus complex patterns with variable L₁ F₂ along the fold axis may develop by a progressive rotation of the geometrically defined fold hinge through successive material lines. The theoretical results have been applied to interpret the lineation patterns in Central Rajasthan, India. It is concluded that L₁ was initially very close to the E-ESE trending subhorizontal Z-axis of bulk deformation during F₂-folding and that the X-axis was subhorizontal or gently plunging with a N-NNE trend.     

A simple criterion for the machinability of hard rocks

Conclusions The application of mechanical methods for rapid excavation requires more detailed and precise knowledge of the site, but there is no single parameter which can provide a comprehensive measure for the selection and performance of a tunnel boring machine.The machinability index proposed in this paper is based on four different parameters which influence the performance of a tunnelling machine and are widely accepted by the engineers and geologists. In order to develop a comprehensive measure regarding the borability of rocks,in situ conditions must be evaluated. The machinability index coupled with thein situ information would facilitate judicious decisions regarding the application and selection of tunnel boring machines.The geological conditions and rock characteristics cannot be controlled but their knowledge can prevent costly mistakes in equipment selection and assist in identifying alternative excavation systems, therefore a thorough site investigation can substantially reduce the economic and technical risks associated with tunnelling and mine development.     

Diffusional theory of formation of secondary dispersion halos in ore deposits

A quasi-diffusion theory of origins of mechanical dispersion halos and a discussion of secondary (epigenetic) dispersion halos of ore bodies overlain by unconsolidated sediments are here presented, including the extent of migration of the ore substances by diffusion. --V. P. Sokoloff.     

Ice ages and orbital variations: Some simple theory and modeling

Possible physical mechanisms relating orbital-element variations (i.e., the “Milankovitch mechanism” of insolation regime changes) to Quaternary glacial/interglacial transitions are explored quantitatively. These include the seasonal cycle of albedo and the zonal distribution of thermal inertia. These mechanisms can interact with the perturbations to zonal average and seasonal average insolation caused by orbital-element variations to cause a global annual temperature residual, even though such variations can cause only a negligible change in global annual insolation.Numerical model experiments with a zonal energy balance model show that the relative interactions between insolation regime changes and seasonally and latitudinally varying albedo and latitudinally varying thermal inertia are roughly of comparable magnitude. Encouraging agreements between model experiments and data are evident, but these (and others') simulations are still a long way away from providing a satisfying explanation of the physical processes that could fully explain the apparent connections between orbital-element variations and Quaternary glaciations.It seems likely that no single physical process can be identified as predominate, and rather, the hypothesized physical connection between insolation regime changes and glacial/interglacial transitions will have to be built on the interactions of a number of processes on both short and long time scales.     

The significance of stretching lineations in terms of progressive deformation and finite strain

Abstract

For a given increment of deformation, stretching lineations can be defined either by old grains or by new grains.

Progressive strain accumulated in a matrix causes reorientation of old grains. The velocity field acting within a grain depends on the degree of non-coaxiality of the progressive strain in the matrix, and on the competence contrast between grain and matrix (e.g. Lister & Williams, 1983). Deformed populations of old grains do not systematically track the principal directions of finite stretch; this depends on the mechanical behavior of the grains. On the other hand, these populations may be good markers of finite strain magnitude, provided that the initial distribution is known.

In contrast, the statistical shape orientation distribution of population of new grains cannot be related in a simple way to the finite strain magnitude, but their preferred orientation is considered to be the best indicator of the principal directions of finite stretch.

An example is considered from the schistes lustrés near Kenestrelle (Val Chisone, Western Alps), where the observed mineral lineation is attributed to a late E-W stretching event in the alpine orogenic history.     

CSAMT 中 Ex 视电阻率与 Ex/Hy 比值视电阻率的对比

常规 CSAMT 勘探是利用电场与磁场的比值来计算卡尼亚视电阻率。通过均匀半空间及层状介质模型,对CSAMT 各场分量进行了计算,对视电阻率定义方式进行了分析。研究结果表明:采用电场 Ex 单分量定义的视电阻率,可以减轻比值视电阻率近区畸变严重的问题。实测资料分析结果进一步验证了 Ex 分量视电阻率的这一优点。在野外 CSAMT 资料采集时不必拘泥比值视电阻率这一种定义方式,可以根据野外实际条件灵活地调整采集方式,提高工作质量和效率。     

Transposition of foliations and superposition of lineations during polyphase deformation in the Nevado-Filabride complex: tectonic implications

International Journal of Earth Sciences - Detailed structural analysis in a ca. 80 km2 area of the western Nevado-Filabride complex (Betic Cordillera) reveals a heterogeneous internal...     

A theory for the shear strength of rockfill

SummaryA Theory for the Shear Strength of Rockfill Existing knowledge of the meaning of the shear strength of rock fill, and of how and why it varies is inadequate.Shear strength is shown to be controlled by the basic angle of friction of rock on rock ( _u ), the voids ratio (e) and the particle breakage (B) and to be dependent on the ratio of major to minor principal stresses.Using statistical methods combined with some simple assumptions based on experimental work formulas are derived for the shear strength of rock fill.Theoretical results are compared with the results of laboratory triaxial tests.

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Zusammenfassung Eine Theorie für die Scherfestigkeit von Gröbstkornschüttungen (Steinbrockenschüttungen). Das vorhandene Wissen vom Wesen der Scherfestigkeit von Gröbstkornschüttungen sowie davon, wie und warum sie verschieden groß ist, ist unzulänglich.Es wird gezeigt, daß die Scherfestigkeit durch den entscheidenden Reibungswinkel von Gestein auf Gestein ( _u ), den Hohlraum-Quotienten (e) und den Bruch von Teilchen (B) bestimmt wird, und daß sie von dem Quotienten aus größter und kleinster Hauptnormalspannung abhängt. Bei der Anwendung statistischer Methoden, welche mit einigen einfachen, auf Versuchen beruhenden Annahmen kombiniert werden, können Formeln für die Scherfestigkeit von Gröbstkornschüttungen abgeleitet werden. Theoretische Ergebnisse werden mit den Ergebnissen von Triaxialversuchen im Labor verglichen.

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Résumé Une théorie pour la résistance au cisaillement des enrochements. Les connaissances actuelles sur la signification de la résistance au cisaillement des enrochements, et sur le pourquoi et le comment de ses variations sont insuffisantes.On montre que la résistance au cisaillement dépend de l'angle de frottement élémentaire rocher sur rocher ( _u ), de l'indice des vides (e) et de la rupture des blocs (B), et qu'elle varie avec le rapport des contraintes principales extrêmes.Grâce à des méthodes statistiques et à quelques hypothèses simples basées sur un travail expérimental, on obtient des formules donnant la résistance au cisaillement des enrochements.Les résultats théoriques sont comparés avec les résultats d'essais triaxiaux au laboratoire.

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With 8 Figures     

A new mechanism for seaward dispersion of midshelf sediments

Silt- to sand-size particles may be transported across middle continental shelves by currents forced by the radiation stress of variable-amplitude swell. With the passage of each group of waves of sufficient amplitude for the high waves in the group to resuspend bottom sediments, there is a seaward bias in the return of sediments to the seafloor. Over a storm season, with the passage of many wave groups, the net seaward sediment displacement may be 1-5 km.     

A simple holistic hypothesis for the self-destruction of ice sheets

Ice sheets are the only components of Earth’s climate system that can self-destruct. This paper presents the quantitative force balance for bottom-up modeling of ice sheets, as first presented qualitatively in this journal as a way to quantify ice-bed uncoupling leading to self-destruction of ice sheets (Hughes, 2009a). Rapid changes in sea level and climate can result if a large ice-sheet self-destructs quickly, as did the former Laurentide Ice Sheet of North America between 8100 and 7900 BP, thereby terminating the last cycle of Quaternary glaciation. Ice streams discharge up to 90 percent of ice from past and present ice sheets. A hypothesis is presented in which self-destruction of an ice sheet begins when ubiquitous ice-bed decoupling, quantified as a floating fraction of ice, proceeds along ice streams. This causes ice streams to surge and reduce thickness by some 90 percent, and height above sea level by up to 99 percent for floating ice, so the ice sheet undergoes gravitational collapse. Ice collapsing over marine embayments becomes floating ice shelves that may then disintegrate rapidly. This floods the world ocean with icebergs that reduce the ocean-to-atmosphere heat exchange, thereby triggering climate change. Calving bays migrate up low stagnating ice streams and carve out the accumulation zone of the collapsed ice sheet, which prevents its recovery, decreases Earth’s albedo, and terminates the glaciation cycle. This sequence of events may coincide with a proposed life cycle of ice streams that drain the ice sheet. A first-order treatment of these life cycles is presented that depends on the longitudinal force balance along the flowbands of ice streams and gives a first approximation to ice-bed uncoupling at snapshots during gravitational collapse into ice shelves that disintegrate, thereby removing the ice sheet. The stability of the Antarctic Ice Sheet is assessed using this bottom-up approach.     

A Late Cretaceous pole for the Pacific plate: implications for apparent and true polar wander and the drift of hotspots

We present a Late Cretaceous (81 Ma) pole position for the Pacific plate derived from paleomagnetic analyses of basalt samples from Detroit Seamount (of the Hawaiian–Emperor seamounts) that were oriented using Brunhes-age overprints. This pole is at much higher latitudes than the previously published Late Cretaceous pole positions based on the modeling of magnetic anomalies observed during marine surveys over seamounts. Our new pole suggests that the Pacific plate would have moved rapidly between 95 and 81 Ma at speeds as high as 19.8 (−10.8/+11.2) cm/year. The Pacific plate at this time was smaller than the present-day plate and had a substantial subducting boundary. The high-velocity estimates are comparable with those of other paleoplates having similar characteristics. Therefore, plate tectonic driving forces can explain the motion and there is no need to invoke true polar wander. Decreases in mantle drag associated with vigorous Late Cretaceous volcanism in the Pacific, however, may have contributed to the rapid plate speed. The new pole position, together with other reliable paleomagnetic indicators of Pacific apparent polar wander, further supports the notion of drift of the Hawaiian hotspot during the Late Cretaceous.