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The paper describes and evaluates an incremental plasticity constitutive model for unsaturated, anisotropic, nonexpansive soils (CMUA). It is based on the modified Cam-Clay (MCC) model for saturated soils and enhances it by introducing anisotropy (via rotation of the MCC yield surface) and an unsaturated compressibility framework describing a double dependence of compressibility on suction and on the degree of saturation of macroporosity. As the anisotropic and unsaturated features can be activated independently, the model is downwards compatible with the MCC model. The CMUA model can simulate effectively: the dependence of compressibility on the level of developed anisotropy, uniqueness of critical state independent of the initial anisotropy, an evolving compressibility during constant suction compression, and a maximum of collapse. The model uses Bishop's average skeleton stress as its first constitutive variable, favouring its numerical implementation in commercial numerical analysis codes (eg, finite element codes) and a unified treatment of saturated and unsaturated material states. 相似文献
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A. G. Anagnostopoulos N. Kalteziotis G. K. Tsiambaos M. Kavvadas 《Geotechnical and Geological Engineering》1991,9(1):1-26
Summary The Corinth Canal crosses the isthmus of Corinth and is of great importance for Mediterranean navigation as well as the railroad and highway connections between southern and central Greece. In the century-long history of the Canal, the slopes have shown only minor stability problems despite their significant length, very steep inclination and, more importantly, the strong earthquakes that have frequently shaken the Corinth area. This type of unsual behaviour has motivated research into the mechanical behaviour of the bluish grey marl which is the main geological formation in the Canal area.Geotechnical investigation of the Corinth Canal marl was performed with an extensive laboratory testing programme on high quality undisturbed samples of the intact marl. The material was shown to exhibit brittle behaviour, high stiffness and significant apparent cohesion at low and moderate stress levels. These characteristics indicate that the material possesses significant structural bonding which is believed to be due to cementation between individual particles, caused by the deposition of carbonates at the time of material genesis. With stressing, the material yields due to a gradual bond degradation. The locus of the initial yield points (yield surface) seems to be an ellipse oriented along the isotropic axis.The testing programme was supplemented with a series of tests on the de-structured marl obtained by thorough remoulding. These tests showed a significant difference in the pre-yield stiffness and the peak strength at low stress levels, but comparable post-rupture shear strengths. 相似文献
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M. Kavvadas B. Papadopoulos N. Kalteziotis 《Geotechnical and Geological Engineering》1994,12(2):87-112
Summary The paper describes an investigation of the geotechnical properties of the Ptolemais lignite (brown coal) and shows that the
soil mechanics principles used in the study of natural and cemented soils are applicable. The material has a high and variable
void ratio incompatible with its preconsolidation pressure, which may be attributed to the existence of structure (chemical
bonding). Bond strength and degradation have been studied and are found to be isotropic, while the stress-strain response
in the prevield domain is intensely cross-anisotropic. The shear strength determined from triaxial CU and CD tests is variable
but strongly dependent on the in situ moisture content. Tests on high quality intact specimens having a wide range of moisture contents (100–150%) verify a hypothesis
that the magnitude of bond strength (expressed by the peak shear strength) is inversely proportional to the moisture content.
A Hvorslev-type normalization process shows that the peak shear strength of the material can be estimated from the in situ moisture content with reasonable accuracy, thus facilitating preliminary stability calculations of production cuts in lignite
mines. The properties of the Ptolemais lignite are compared with the properties of a lignite from another location in Greece
(Megalopolis) and an Australian lignite (Morwell). It is shown that the shear strength characteristics of the lignite types
studied are similar and strongly dependent on the in situ moisture content, which seems to be a measure of the magnitude of inter-particle bonding. 相似文献
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Geotechnical and Geological Engineering - The construction of twin tunnels is a mandatory guideline and a prevailing practice in either conventional or mechanized tunneling. Nevertheless, most of... 相似文献
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M. Kavvadas A. Giolas G. Papacharalambous 《Geotechnical and Geological Engineering》1992,10(2):141-157
Summary The paper provides the approximate closed-form expressions for the estimation of the amount of ground water infiltration, the seepage exit gradient and the hydraulic pressure distribution on the cutoff elements in the case of sheeted excavations below the water table. The expressions are obtained by a multiple regression-type fitting of the results of an extensive parametric finite-element analysis for the two-dimensional steady-state flow in the soil around a sheeted excavation. In addition to the problem geometry, the effects of an impermeable base and a thin low permeability layer penetrated by the sheeting are also studied. The predictions of the approximate expressions deviate from the corresponding finite-element results by less than 15%, for a wide range of geometries and soil characteristics. It is shown how shape factors might be used to adapt the semi-empirical formulae for the case of excavations with limited length (circular and rectangular). 相似文献
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The paper presents an incremental plasticity constitutive Model for Structured Soils (MSS–2) to describe the effects of structure (stress history and bonding) on the mechanical behaviour of cohesive soils. Such effects are high initial stiffness, dilatancy and peak strength, their appreciable reduction upon strain-induced de-structuring and the evolution of material anisotropy. The proposed model advances present practice in incremental elasto-plasticity for structured soils by incorporating: (a) distorted ellipsoids, rotated with respect to the isotropic axis, for the Structure Strength Envelope (bounding surface) and the Plastic Yield Envelope (yield surface) to describe the evolution of structure and anisotropy, (b) an Intrinsic Compressibility Framework and a corresponding Intrinsic Strength Envelope which represents a lower bound of the Structure Strength Envelope and is used as reference locus for the structureless material, (c) an improved damage mechanism to model structure degradation by plastic strains and (d) a non-associated flow rule controlled by structure. The proposed model is modular, its features can be activated simultaneously or selectively, and the 3-D tensorial formulation facilitates direct implementation in finite elements codes. 相似文献
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