Geotechnique
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Traditional soil particle sphericity, roundness and surface roughness by computational geometry Definitions of soil particle sphericity, roundness and roughness have existed since at least the 1930s. In the 1950s, charts of typical sphericity and roundness values were developed to alleviate tedious manual determination. They allowed users to classify particles by visual comparison to typical particles possessing ranges of sphericity and roundness. The original definitions and somewhat subjective chart methods are still widely used today. This paper describes robust numerical methods based on computational geometry to determine precisely the traditional values from two-dimensional images of particles. Statistical methods including locally weighted regression and K-fold cross-validation were used to discretise a mean particle surface and thereby quantify and remove roughness. The paper details the algorithms for identifying particle corners and fitting circles to them for computation of roundness. Conclusions are also drawn regarding the most appropriate definition for particle sphericity from among five that are commonly cited. Finally, recommendations are made for the minimum image resolutions and particle perimeter discretisation necessary to obtain accurate results.
Geotechnique - Tập 65 Số 6 - Trang 494-506 - 2015
Strain localization and periodic flucations in granular flow processes from hoppers Patterns of discharge processes of a granular material from plane containers are presented briefly. Rupture surfaces, interpreted here as shear bands, are a distinct feature of the flow patterns. Either a shock-like or a material character is attributed to the shear bands. A technique is shown for calculation of the energy dissipation rate within shear bands in softening materials. This technique is used in the limit analysis type of approach to the problem of extrusion of a strain-softening material through a pair of smooth flat dies, and to the discharge process of a granular material from a container. It is shown that the energy dissipation rate within a shear band in a non-steady (periodic) process may be lower than that in a steady-state flow. It is demonstrated that, if a criterion of minimum effort is used, periodic fluctuations in deformation patterns of softening materials can be predicted. The proposed analysis is size-sensitive; the scale effect is introduced through the assump tion that the shear band thickness is a material property. It is essential for the analysis that deformation mechanisms are considered as processes, not as incipient flow mechanisms (which is the case in the classical kinematical approach of limit analysis). L'article présent brièvement des types de processus de déchargement d'une matière granuleuse à partir d'un récipient plat. Des surfaces de rupture, interprétées comme des bandes de cisaillement, forment une caractéristique très marquée de ces types d'écoulement. On attribue aux bandes de cisaillement une nature analogue à un impact ou bien une nature materielie. Une technique est présentée pour calculer la vitesse de dissipation d'énergie à l'intérieur des bandes dans des matières qui se ramollissent. Cette technique est utilisée dans l'analyse limite appliquée à l'extrusion d'une matière qui se ramollit à travers une paire de matrices planes et lisses et aussi au processus de déchargement d'une matière granuleuse à partir d'un récipient. On montre que la vitesse de dissipation d'énergie a' l'intérieur d'une bande de cisaillement dans un processus non-stationnaire (périodique) peut être inférieure à celle dans un éconlement stationnaire. Il est démontré que si on emploie un critère d'effort minimal, des variations périodiques dans les types de déformation des matières qui se ramolliint peuvent être prédites. L'analyse proposée dépend des grandeurs, l'effet d'échelle étant intro&t par l'hypothèse que l'épaisseur de la bande de cisaillement est une propriéte du materiau. Pour cette analyse il est essentiel que les mécanismes de déformation soient considérés comme des processus et non comme des mécanismes naissants d'écoulement, comme dans le cas de la méthode cinématique traditionnelle d'analyse limite.
Geotechnique - Tập 40 Số 3 - Trang 389-403 - 1990
CPT-based liquefaction analysis, Part 1: Determination of limit state function This paper is the first of a set of two papers that address the issue of earthquake-induced liquefaction potential. In this paper, a CPT-based limit state function for assessing the cyclic liquefaction resistance of sandy soils is presented. The liquefaction resistance of a soil is generally expressed as cyclic resistance ratio (CRR), while the seismic load that causes liquefaction is expressed as cyclic stress ratio (CSR). By definition, CRR is equal to the maximum CSR that a soil can sustain without the occurrence of cyclic liquefaction. In the present study, a new method to establish a limit state function for evaluating cyclic liquefaction resistance is developed. This new method is based on an artificial neural network (ANN) modelling and analysis of 225 field liquefaction performance records. First, an ANN model is developed to predict the occurrence of liquefaction based on historic field performance records. Second, a search procedure is developed to locate data points on the limit state surface. Third, another ANN model is created to approximate the multi-variable limit state function. The established approximate function, an ANN model, can be used to determine the CRR of a soil using CPT data. The developed CPT-based limit state function forms the basis for the development of a risk-based method for assessing cyclic liquefaction potential.
Geotechnique - Tập 50 Số 5 - Trang 583-592 - 2000
A Method of Estimating the California Bearing Ratio of Cohesive Soils from Plasticity Data Synopsis The Paper shows that to a first approximation the California bearing ratio (CBR) of a remoulded soil can be deduced from the estimated bearing capacity of the soil, which itself can be deduced from a knowledge of the suction of the remoulded soil and its true angle of friction. It is also shown that the suction of such a remoulded soil and its true angle of friction can be inferred from a knowledge of the liquid and plastic limits and moisture content of the soil, thus allowing the CBR and its variation with moisture content to be estimated from the results of the various plasticity tests. If the degree of saturation is known, the variation of CBR with air content can also be deduced. Worked examples are given showing how the method described in the Paper is used to estimate CBR values for a variety of practical conditions. L'Exposé fait apparaître qu'à une première approximation, le coefficient de charge de Californie (California bearing ratio (CBR)) d'un sol remanié peut être déduit à partir de la capacité de charge estimée du sol, qui peut elle-même être déduite de la connaissance de la suction du sol remané et de son angle réel de frottement. Il apparait aussi que la suction d'un tel sol remanié et son angle réel de frottement peuvent être déduits de la connaissance des limites de plasticité et de l'état liquide et de la teneur en eau du sol, permettant ainsi que le CBR et sa variation correspondant à la teneur en eau soient estimés à partir des résultats des différents essais de plasticité. Si le degré de saturation est connu, la variation du CBR selon la teneur en air peut aussi être déduite. Des exemples avec les opérations effectées sont donnés montrant comment la méthode qui est dérite dans l'exposé est employée pour estimer les valeurs CBR en fonction de conditions pratiques variées.
Geotechnique - Tập 12 Số 4 - Trang 271-282 - 1962
Sea-Level Movements and the Geologic Histories of the Post-Glacial Marine Soils at Boston, Nicolet, Ottawa and Oslo Synopsis The Paper is divided into two separate parts; the first part deals with eustatic sea-level movements which have occurred during the past 20,000 years, and the second part concerns the geologic history of marine soil deposits at Boston, Nicolet, Ottawa, and Oslo. Eustatic sea-level movements are determined by synthesizing direct and indirect evidence concerning sea-level movements. Direct evidence consists of the ages and elevations of marine fossils and other materials, and elevations and ages of deposition and erosion surfaces which were controlled by sea-level movements. Indirect evidence consists of the dates of climate and temperature changes and the dates of major activity of the continental glaciers. From these data a provisional sea-level movement curve has been drawn for the period extending over the past 20,000 years. Geologic histories of marine soil deposits are dependent on, among other things, sea-level and local crustal movements. For each of the above mentioned sites, time curves of sea-level and crustal movements are drawn, and from a study of these curves and other geological evidence, the general geologic history of the soils at each site is determined. Geotechnical data are presented in the form of boring profiles and results of laboratory tests, and these are discussed with respect to the previously determined geologic history. In certain cases there are apparent discrepancies between the geologic histories and the interpretations of geotechnical data, and these apparent discrepancies are commented upon. L'article a été devisé en deux parties. La première traite les mouvements eustatiques de la mer pendant les dernières 20,000 années, et la seconde s'occupe de l'histoire géologique des dépôts de sol à Boston, Nicolet, Ottawa et Oslo. Les mouvements eustatiques du niveau de la mer sont déterminés ainsi qu'on synthèse les évidences directes et indirectes concernant ces mouvements. L'évidence directe se compose des âges et des élévations des fossiles marins et d'autres matériels, et des élévations et des âges des dépôts et surfaces d'érosion qui ont été réglés par ces mouvements du niveau de la mer. L'évidence indirecte se compose des dates concernant le climat et les changes de la température, et les dates concernant les activités majeures des glaciers continentaux. On a dessiné sur la base de ces données une courbe provisoire des mouvements du niveau de la mer pour la période des demières 20,000 années. Les histoires géologiques des sols marins dépendent, parmi d'autres chases, sur le niveau de la mer et les mouvements locals de la crôute. On a dessiné des courbes de mouvements de la crôute et du niveau de la mer pour chacun de ces terrains mentionés. Sur la base de ces courbes et d'autres évidences géologiques on a déterminé l'histoire géologique de ces terrains. Les donées géotechniques sont presentées en forme des profiles de forage et des résultats des investigations laboratoires, et on discute ces données en regard des histoires géologiques préalablement déterminées. Dans certains cas on trouve un désaccord apparent entre les histoires géologiques et l'interprétation des donées géotechniques, et ces déaccords sont commentées.
Geotechnique - Tập 14 Số 3 - Trang 203-230 - 1964
Tunnels in sands: the effect of size, depth and volume loss on greenfield displacements This paper examines the effect that tunnel size, depth and volume loss have on greenfield soil displacements above tunnels in sandy ground. The results of a series of plane-strain centrifuge tests performed on tunnels in a dry silica sand are examined. The cover-to-diameter ratio, C/D, of the tunnels ranged from 1·3 to 4·4. Features of greenfield settlement trough shape, both surface and subsurface, are illustrated by examining soil displacement data obtained using an image-based deformation measurement technique. The effects of tunnel size, depth and volume loss are demonstrated, and the suitability of typical fitting curves is discussed. The complex volumetric behaviour of drained soil is illustrated by comparing tunnel volume loss with the volume loss experienced by the soil. A set of equations is developed that provide a method of evaluating the change of settlement trough shape with tunnel size, depth and volume loss.
Geotechnique - Tập 62 Số 5 - Trang 385-399 - 2012
Assessment of strength development in cement-admixed high water content clays with Abrams' law as a basis
Geotechnique - Tập 53 Số 4 - Trang 439-444 - 2003
Stability Coefficients for Earth Slopes Synopsis The application of the effective stress analysis to earth slopes has suffered through lack of a general solution such as that presented by Taylor (1937) for the total stress analysis. Recent developments in computing technique have been applied to the slip circle method and have made it possible to present the results of the effective stress analysis in terms of stability coeffcients from which the factor of safety can be rapidly obtained. Illustrations are given of the use of these coefficients with the distributions of pore pressure encountered in typical earth dams and cuts. L'application de principe des tensions efficace sur l'analyse des pentes de terre c'est empëcher de l'absence d'une solution générale, telle que celle du Taylor (1937) pour l'analyse des pentes en termes des tensions totales. L'application des progrès récents dans la technique de computation, à la méthode du cercle de glissement, a rendu possible la présentation des résultats en termes de coef-ficients de stabilitté, baser sur le principe des tensions efficace, dont on peut obtenir rapidement le facteur de sécurité. Ici, on donne des illustrations graphiques sur l'emploi de ces coefficients avec la répartition des pressions interstitielles rencontrée dans des talus et des tranchées de terre typique.
Geotechnique - Tập 10 Số 4 - Trang 129-153 - 1960
A unique relationship for χ for the determination of the shear strength of unsaturated soils
Geotechnique - Tập 52 Số 1 - Trang 76-77 - 2002
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