Analytical and numerical analyses of the load‐bearing capacity of retaining walls laterally supported at both ends

This paper investigates the load‐bearing capacity of a perfectly smooth retaining wall laterally supported at both ends assuming that the wall fails by the development of three plastic hinges. The study considers the case of a cohesionless elastic–perfectly plastic backfill with a Mohr–Coulomb yield criterion and an associative flow rule in drained conditions. A kinematically admissible soil–structure failure mechanism is proposed and compared with the conventional solutions and with results from a numerical finite element modelling. The study shows that the proposed solution and the numerical solution are in good agreement. These solutions are found to be much more favourable for the wall than the conventional solutions. Copyright © 2010 John Wiley & Sons, Ltd.     

Deterministic ground motion simulations with shallow crust nonlinearity at Garner Valley in Southern California

We present deterministic ground motion simulations that account for the cyclic multiaxial response of sediments in the shallow crust. We use the Garner Valley in Southern California as a test case. The multiaxial constitutive model is based on the bounding surface plasticity theory in terms of total stress and is implemented in a high‐performance computing finite‐element parallel code. A major advantage of this model is the small number of free parameters that need to be calibrated given a shear modulus reduction curve and the ultimate soil strength. This, in turn, makes the model suitable for regional‐scale simulations, where geotechnical data in the shallow crust are scarce. In this paper, we first describe a series of numerical experiments designed to verify the model implementation. This is followed by a series of idealized large‐scale simulations in a 35 26 4.5 km domain that encompasses the Garner Valley downhole array site, which is an instrumented and well‐characterized site in Southern California. Material properties were extracted from the Southern California Earthquake Center Community velocity model, CVM‐S4.26, considering its optional geotechnical layer, while the modulus reduction curves and soil strength were selected empirically to constrain the nonlinear soil model parameters. Our nonlinear simulations suggest that peak ground displacements within the valley increase relative to the linear case, while peak ground accelerations can increase or decrease, depending on the frequency content of the excitation. The comparisons of our simulations against hybrid three‐dimensional–one‐dimensional site response analyses suggest the inadequacy of the latter to capture the complexity of fully three‐dimensional simulations.     

Homogenization estimates for texture evolution in halite

In this work, the recently developed “second-order” self-consistent method [Liu, Y., Ponte Castañeda, P., 2004a. Second-order estimates for the effective behavior and field fluctuations in viscoplastic polycrystals. J. Mech. Phys. Solids 52 467–495] is used to simulate texture evolution in halite polycrystals. This method makes use of a suitably optimized linear comparison polycrystal and has the distinguishing property of being exact to second order in the heterogeneity contrast. The second-order model takes into consideration the effects of hardening and of the evolution of both crystallographic and morphological texture to yield reliable predictions for the macroscopic behavior of the polycrystal. Comparisons of these predictions with full-field numerical simulations [Lebensohn, R.A., Dawson, P.R., Kern, H.M., Wenk, H.R., 2003. Heterogeneous deformation and texture development in halite polycrystals: comparison of different modeling approaches and experimental data. Tectonophysics 370 287–311], as well as with predictions resulting from the earlier “variational” and “tangent” self-consistent models, included here for comparison purposes, provide insight into how the underlying assumptions of the various models affect slip in the grains, and therefore the texture predictions in highly anisotropic and nonlinear polycrystalline materials. The “second-order” self-consistent method, while giving a softer stress-strain response than the corresponding full-field results, predicts a pattern of texture evolution that is not captured by the other homogenization models and that agrees reasonably well with the full-field predictions and with the experimental measures.     

Critical Slope and Plasticity

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The geotechnical properties and behaviour of a pro-glacial lake clay, and its cementitious stabilization

The Tees Laminated Clay forms a continuous deposit around the Tees estuary in north east England and was deposited in a proglacial lake which occupied the Teesside area during late Devensian times, disappearing about 13 000 years ago. It overlies till, with which it has a sharp contact and reaches a maximum thickness in parts of central Middlesbrough of just over 9 m. The laminations consist of alternating thin layers of clay and silt, and represent seasonal increments of sediment. Kaolinite and illite, with lesser amounts of chlorite, dominate the mineral composition. Quartz tends to account for less than 35%. The notable carbonate content may be diagenetic in origin. The birefringence ratio of the clay minerals indicates a medium degree of particle orientation which suggests a partially flocculated fabric.This laminated clay has a high plasticity. However, the liquid and plastic limits of the silty layers differ significantly from those of the clay layers or the bulk samples. The clay fraction has a greater influence on these limits than the silty fraction. In addition, the linear shrinkage, liquidity indices and consistency indices of the silty layers differ appreciably from those of the clay layers and the bulk samples. The laminated clay is inactive. The orientation of the laminations in relation to the direction of maximum principal stress influences the shear strength, the lowest strengths being developed when these orientations are between 30° and 60°. The stress paths, anisotropic ratios and values of Af indicate that the Tees Laminated Clay is normally consolidated or lightly overconsolidated. The McLamore–Gray concept possibly can be applied to the anisotropic strength behaviour.Tees Laminated Clay can give rise to problems during construction operations since it can lose strength significantly on remoulding. Accordingly, these soils were treated with cementitious materials to determine the extent to which their engineering behaviour was enhanced by the addition of such materials. © Rapid Science Ltd. 1998     

加筋砂土作用在挡土墙上的土压力研究

以土的塑性极限分析理论和拱体理论为基础，结合挡土墙的长高比，提出了墙后砂土的两种三维破坏模式，并把两种模式与加筋相结合，求出了在加筋水平间距Sx和竖向间距Sx下作用在墙上主动土压力的上限解和设计的加筋长度。最后通过实例验证了本文的理论。     

Comments on Modelling Short Atmospheric Frontal Waves

The idea of Gerstner's trochoidal waves is used to reconstruct a model of short, finite-amplitude progressive waves on frontal surfaces of the Margules Type. Stable waves associated with a negative (westward) group velocity occur in the model. A wave train can be maintained through the formation of new waves in the rear of the existing waves as a result of the westward energy transport.     

Unbiased estimation of flood risk with the GEV distribution

Conventional flood frequency analysis is concerned with providing an unbiased estimate of the magnitude of the design flow exceeded with the probabilityp, but sampling uncertainties imply that such estimates will, on average, be exceeded more frequently. An alternative approach is therefore, to derive an estimator which gives an unbiased estimate of flow risk: the difference between the two magnitudes reflects uncertainties in parameter estimation. An empirical procedure has been developed to estimate the mean true exceedance probabilities of conventional estimates made using a GEV distribution fitted by probability weighted moments, and adjustment factors have been determined to enable the estimation of flood magnitudes exceeded with, on average, the desired probability.     

基于广义塑性力学的土体次加载面循环塑性模型(Ⅰ): 理论与模型

简要地介绍了次加载面理论的基本思想、假设及其物理解释。在广义塑性力学的框架内，引入次加载面的思想，把常规的椭圆-抛物线双屈服面模型，扩展为次加载面循环塑性模型，以反映循环荷载作用下土体的曼辛效应与棘轮效应。模型能考虑塑性应变增量对应力增量的相关性，既能反映土体的循环加载特性，又能反映正常固结土和超固结土的单调加载特性。     

A constitutive model for bonded geomaterials subject to mechanical and/or chemical degradation

The mechanical behaviour of bonded geomaterials is described by means of an elastoplastic strain‐hardening model. The internal variables, taking into account the ‘history’ of the material, depend on the plastic strains experienced and on a conveniently defined scalar measure of damage induced by weathering and/or chemical degradation. For the sake of simplicity, it is assumed that only internal variables are affected by mechanical and chemical history of the material. Despite this simplifying assumption, it can be shown that many interesting phenomena exhibited by weathered bonded geomaterials can be successfully described. For instance, (i) the transition from brittle to ductile behaviour with increasing pressure of a calcarenite with collapsing internal structure, (ii) the complex behaviour of chalk and other calcareous materials in oedometric tests, (iii) the chemically induced variation of the stress and strain state of such kind of materials, are all phenomena that can be qualitatively reproduced. Several comparisons with experimental data show that the model can capture the observed behaviour also quantitatively. Copyright © 2003 John Wiley & Sons, Ltd.