The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Masaki Nakano - One of the best experts on this subject based on the ideXlab platform.
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Interpretation of the mechanical behavior of embankments having various compaction properties based on the soil skeleton structure
Soils and Foundations, 2015Co-Authors: Takayuki Sakai, Masaki NakanoAbstract:Abstract After the Hanshin Awaji Earthquake disaster, the seismic resistance of embankments was evaluated, and design principles were changed from specification-based to performance-based. However, compaction properties and the mechanical behavior of compacted soil were not sufficiently considered in the Manual of Highway Earthworks on Embankments. The first objective of the present study is to reproduce the mechanical behavior of three embankment materials having different compaction properties. A series of triaxial compression tests and oedometer tests is carried out. The mechanical behavior is reproduced by the SYS Cam-clay model and the influence of compaction on the mechanical behavior is interpreted based on the soil skeleton structure. The second objective is to evaluate the seismic stability of the embankment, which depends on the compaction properties of the embankment material, using GEOASIA, a soil–water coupled finite deformation analysis code. The primary conclusions are as follows. (1) Through the triaxial tests, the maximum deviator stress increases as the degree of compaction, Dc, increases. However, the trends in the increase differ depending on the material. (2) Based on one-dimensional consolidation tests, the compression curve is approximately a straight line with a large vertical effective stress. In the present study, a greater maximum dry density corresponds to less compressibility and a lower compression curve. (3) The mechanical behavior of each material is reproduced by the SYS Cam-clay model using one set of material constants for each material and representing the differences in Dc by different initial conditions for the structure and Overconsolidation. An increase in Dc causes the decay of the structure, as well as the accumulation of Overconsolidation. In the case of material A, the decay of the structure and the loss of Overconsolidation occur quickly, whereas in the case of material C, the decay of the structure is slight and the loss of Overconsolidation is moderate. (4) The seismic response analysis reveals different deformations of the embankment for different materials, even for the same Dc. The seismic stability of the embankments was increased by increasing Dc. Materials, such as material A, that have fast decay of the structure and fast loss of Overconsolidation produce embankments with high seismic stability.
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mechanical behavior of compacted geomaterial changed from the dredged soil in nagoya port by mixing with some stabilizers
GeoShanghai 2010 International ConferenceShanghai Society of Civil EngineeringChinese Institute of Soil Mechanics and Geotechnical EngineeringAmerican, 2010Co-Authors: Masaki Nakano, Eiji Yamada, Akira AsaokaAbstract:To solve the problem of accumulation of huge amount of dredged soil (DS) in Nagoya Port Island, some kinds of stabilizers are mixed with the dredged soil to improve the mechanical properties, and then the treated soils can be used as geomaterial. A series of laboratory tests were carried out to investigate the mechanical behaviors of these soils, and also SYS Cam-clay model was adopted to interpret these behaviors by evolutions of soil skeleton structure theoretically. It is suggested that DS behaves like typical clay, which is difficult to decay structure and easy to lose Overconsolidation. Compared with DS, these treated soils are in highly-structured and heavily-overconsolidated state. Moreover, the treated soils change to be new materials with slow rate in both decay of structure and loss of Overconsolidation. The strength of treated soils is therefore promoted compared with DS and can be used as a new kind of construction material.
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A Description of Mechanical Behavior of Clay and Sand Based on Evolutions of Soil-Structure and Overconsolidation
Geomechanics, 2005Co-Authors: Masaki Nakano, Kentaro Nakai, Akira AsaokaAbstract:Natural soils are often a highly structured state and they are more or less in an overconsolidated state. Assuming that the Cam-clay model describes the loading behavior of fully remolded and normally consolidated soils, Asaoka et al. introduced new superloading and subloading surfaces added to the plastic potential of the modified Cam-clay model. In this constitutive model, the effects of decay of the soil structure, loss of Overconsolidation and evolution of anisotropy are mutually discussed concerning their relationship with ongoing plastic deformation. Clay is clearly distinguished from sand simply by the difference in the rates of these three evolution laws. In clay, the rate of decay of the soil structure is much slower than the rate of the loss of Overconsolidation, while in sand, the rate of the decay/collapse of the soil structure is faster than the rate of loss of Overconsolidation. In the present study, fundamental constitutive model responses of natural clay are illustrated through the numerical simulation of undrained and drained triaxial compression behavior. The response of the normally consolidated and overconsolidated clays exhibits typical natural clay shear behavior, based on the three evolution laws. For sand, typical model responses are illustrated through the numerical simulation of the compaction procedure of loose sand. Repeated application of low-level shear stress upon loose sand yields a huge amount of volume compression, which is due to the rapid collapse of the initial soil structure. Repetition of the loading also results in a rapid increase of the Overconsolidation ratio. Drained and undrained shear behavior of sand changes remarkably with the change of density during compaction, which the model described in this study consistently predicts using a single set of soil parameters.
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DELAYED COMPRESSION/CONSOLIDATION OF NATURAL CLAY DUE TO DEGRADATION OF SOIL STRUCTURE
Soils and Foundations, 2000Co-Authors: Akira Asaoka, Toshihiro Noda, Masaki Nakano, Kazuhiro KanedaAbstract:The superloading yield surface concept applied to the original Cam-clay model is examined for the application to the one-dimensional consolidation problems of highly structured soils. When the proposed elasto-plastic constitutive model is taken to be the case for a structured soil, the one-dimensional consolidation computation clarifies the following : (1) Delayed consolidation should occur even under one-dimensional compression condition with a considerably low stress ratio when softening of the soil occurs with volume compression. The delayed consolidation is the consolidation process that has sometimes been referred to as "secondary compression". (2) The structure is always degrading as plastic deformation proceeds even within the period of "secondary compression". (3) The decay of Overconsolidation to normal consolidation also proceeds with plastic deformation. In this sense, the degradation of structure can not be independent of the decay of Overconsolidation. However, since the decay of Overconsolidation is much faster than the degradation of structure in clay, then softening becomes possible with volume compression even under a considerably low stress ratio. Recovery of structure with time due to chemical bonding effects etc. in soil particles is beyond the scope of this study.
George A. Athanasopoulos - One of the best experts on this subject based on the ideXlab platform.
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Preconsolidation versus Aging Behavior of Kaolinite Clay
Journal of Geotechnical Engineering, 1993Co-Authors: George A. AthanasopoulosAbstract:Resonant column test results were used to determine the effects of the Overconsolidation ratio (OCR) and of aging on the normalized rate of secondary increase of low amplitude shear modulus, N sub G, of a remolded kaolinite clay. It was found that N sub G decreases linearly with the logarithm of OCR. Comparing this behavior with the similar effect of aging on the value of N sub G, a correlation was developed between duration of aging and equivalent Overconsolidation ratio, OCR sub eq. The details of the study are described, and the results are discussed.
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Effects of ageing and Overconsolidation on the elastic stiffness of a remoulded clay
Geotechnical & Geological Engineering, 1993Co-Authors: George A. AthanasopoulosAbstract:Results of resonant column tests were used to determine values of low amplitude shear modulus ( G _0) of a remoulded kaolinite clay for different durations of ageing and for different values of consolidation stress ( σ ′_0) and Overconsolidation ratio (OCR). It was found that after completion of primary consolidation the values of G _0 increased linearly with the logarithm of time and after a week of confinement the value of normalized rate of secondary increase of shear modulus ( N _ G ) could be reliably estimated. Values of N _ G were found to derease linearly with the logarithm of OCR and with the logarithm of ageing duration. This similarity of behaviour provided a basis for establishing an equivalency between age and equivalent Overconsolidation ratio (OCR)_eq. The effects of σ ′_0 and OCR on the value of G _0 were also established in a functional form that indicated a stronger influence compared to that predicted by the Hardin Equation.
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Effects of ageing and Overconsolidation on the elastic stiffness of a remoulded clay
Geotechnical & Geological Engineering, 1993Co-Authors: George A. AthanasopoulosAbstract:Results of resonant column tests were used to determine values of low amplitude shear modulus ( G _0) of a remoulded kaolinite clay for different durations of ageing and for different values of consolidation stress ( σ ′_0) and Overconsolidation ratio (OCR). It was found that after completion of primary consolidation the values of G _0 increased linearly with the logarithm of time and after a week of confinement the value of normalized rate of secondary increase of shear modulus ( N _ G ) could be reliably estimated. Values of N _ G were found to derease linearly with the logarithm of OCR and with the logarithm of ageing duration. This similarity of behaviour provided a basis for establishing an equivalency between age and equivalent Overconsolidation ratio (OCR)_eq. The effects of σ ′_0 and OCR on the value of G _0 were also established in a functional form that indicated a stronger influence compared to that predicted by the Hardin Equation.
Toshihiro Noda - One of the best experts on this subject based on the ideXlab platform.
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Determination of Parameter in SYS Cam-Clay Model of Ultra-Soft Clay
Applied Mechanics and Materials, 2015Co-Authors: Bin Bin Xu, Toshihiro NodaAbstract:Parameter analyses in the constitutive model determine the precision of numerical results. Cam-clay model is the first elasto-plastic model in the world and widely used in the practical engineering. SYS Cam-clay model is proposed based on Cam-clay model by incorporating the concept of Overconsolidation, soil structure and anisotropy. There are two groups of parameters in this model, elasto-plastic parameters that are exactly same as those in Cam-clay model and evolutional parameters that decide the variation of Overconsolidation, soil structure and anisotropy. The detailed process to determine the parameters is introduced step by step.
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Sensitivity Analysis of Parameters in SYS Cam-Clay Model
Advanced Materials Research, 2014Co-Authors: Toshihiro Noda, Kentaro NakaiAbstract:The SYS Cam-clay model, which is extended based on the Cam-clay model and the critical state theory, is able to describe the heavily overconsolidated and structure soils. However compared with Cam-clay model with five elasto-plastic parameters there are six additional evolutional parameters in SYS Cam-clay model and the sensitivity analysis of the new added parameters should be carried out. Through the calculation of constitutive response assuming the uniform deformation field, the sensitivities of degradation index of structure, degradation index of Overconsolidation ratio and rotational hardening index are investigated respectively. It can be seen that the peak strength and the “rewinding behavior” in the effective stress path are influenced greatly while there is no coupling effect of these parameters mutually. The initial Overconsolidation ratio and degree of structure also have an effect on the mechanical behavior and the initial specific volume.
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DELAYED COMPRESSION/CONSOLIDATION OF NATURAL CLAY DUE TO DEGRADATION OF SOIL STRUCTURE
Soils and Foundations, 2000Co-Authors: Akira Asaoka, Toshihiro Noda, Masaki Nakano, Kazuhiro KanedaAbstract:The superloading yield surface concept applied to the original Cam-clay model is examined for the application to the one-dimensional consolidation problems of highly structured soils. When the proposed elasto-plastic constitutive model is taken to be the case for a structured soil, the one-dimensional consolidation computation clarifies the following : (1) Delayed consolidation should occur even under one-dimensional compression condition with a considerably low stress ratio when softening of the soil occurs with volume compression. The delayed consolidation is the consolidation process that has sometimes been referred to as "secondary compression". (2) The structure is always degrading as plastic deformation proceeds even within the period of "secondary compression". (3) The decay of Overconsolidation to normal consolidation also proceeds with plastic deformation. In this sense, the degradation of structure can not be independent of the decay of Overconsolidation. However, since the decay of Overconsolidation is much faster than the degradation of structure in clay, then softening becomes possible with volume compression even under a considerably low stress ratio. Recovery of structure with time due to chemical bonding effects etc. in soil particles is beyond the scope of this study.
Theodoros Triantafyllidis - One of the best experts on this subject based on the ideXlab platform.
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AVISA: anisotropic visco-ISA model and its performance at cyclic loading
Acta Geotechnica, 2020Co-Authors: Merita Tafili, Theodoros TriantafyllidisAbstract:In this work, a constitutive model able to capture the strain rate dependency, small strain effects and the inherent anisotropy is proposed considering the influence of the Overconsolidation ratio (OCR). Small strain effects are captured by using an extended ISA plasticity formulation (Fuentes and Triantafyllidis in Int J Numer Anal Methods Geomech 39(11):1235–1254, 2015). The strain rate dependency is reproduced by incorporating a third strain rate mechanism (in addition to the elastic and hypoplastic strain rate). A loading surface has been incorporated to define a three-dimensional (3D) Overconsolidation ratio and to account for its effects on the simulations. Experimental investigations using Kaolin Clay and Lower Rhine Clay with horizontal bedding plane have shown that under undrained cycles of small strain amplitudes ( $$
Akira Asaoka - One of the best experts on this subject based on the ideXlab platform.
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mechanical behavior of compacted geomaterial changed from the dredged soil in nagoya port by mixing with some stabilizers
GeoShanghai 2010 International ConferenceShanghai Society of Civil EngineeringChinese Institute of Soil Mechanics and Geotechnical EngineeringAmerican, 2010Co-Authors: Masaki Nakano, Eiji Yamada, Akira AsaokaAbstract:To solve the problem of accumulation of huge amount of dredged soil (DS) in Nagoya Port Island, some kinds of stabilizers are mixed with the dredged soil to improve the mechanical properties, and then the treated soils can be used as geomaterial. A series of laboratory tests were carried out to investigate the mechanical behaviors of these soils, and also SYS Cam-clay model was adopted to interpret these behaviors by evolutions of soil skeleton structure theoretically. It is suggested that DS behaves like typical clay, which is difficult to decay structure and easy to lose Overconsolidation. Compared with DS, these treated soils are in highly-structured and heavily-overconsolidated state. Moreover, the treated soils change to be new materials with slow rate in both decay of structure and loss of Overconsolidation. The strength of treated soils is therefore promoted compared with DS and can be used as a new kind of construction material.
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A Description of Mechanical Behavior of Clay and Sand Based on Evolutions of Soil-Structure and Overconsolidation
Geomechanics, 2005Co-Authors: Masaki Nakano, Kentaro Nakai, Akira AsaokaAbstract:Natural soils are often a highly structured state and they are more or less in an overconsolidated state. Assuming that the Cam-clay model describes the loading behavior of fully remolded and normally consolidated soils, Asaoka et al. introduced new superloading and subloading surfaces added to the plastic potential of the modified Cam-clay model. In this constitutive model, the effects of decay of the soil structure, loss of Overconsolidation and evolution of anisotropy are mutually discussed concerning their relationship with ongoing plastic deformation. Clay is clearly distinguished from sand simply by the difference in the rates of these three evolution laws. In clay, the rate of decay of the soil structure is much slower than the rate of the loss of Overconsolidation, while in sand, the rate of the decay/collapse of the soil structure is faster than the rate of loss of Overconsolidation. In the present study, fundamental constitutive model responses of natural clay are illustrated through the numerical simulation of undrained and drained triaxial compression behavior. The response of the normally consolidated and overconsolidated clays exhibits typical natural clay shear behavior, based on the three evolution laws. For sand, typical model responses are illustrated through the numerical simulation of the compaction procedure of loose sand. Repeated application of low-level shear stress upon loose sand yields a huge amount of volume compression, which is due to the rapid collapse of the initial soil structure. Repetition of the loading also results in a rapid increase of the Overconsolidation ratio. Drained and undrained shear behavior of sand changes remarkably with the change of density during compaction, which the model described in this study consistently predicts using a single set of soil parameters.
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DELAYED COMPRESSION/CONSOLIDATION OF NATURAL CLAY DUE TO DEGRADATION OF SOIL STRUCTURE
Soils and Foundations, 2000Co-Authors: Akira Asaoka, Toshihiro Noda, Masaki Nakano, Kazuhiro KanedaAbstract:The superloading yield surface concept applied to the original Cam-clay model is examined for the application to the one-dimensional consolidation problems of highly structured soils. When the proposed elasto-plastic constitutive model is taken to be the case for a structured soil, the one-dimensional consolidation computation clarifies the following : (1) Delayed consolidation should occur even under one-dimensional compression condition with a considerably low stress ratio when softening of the soil occurs with volume compression. The delayed consolidation is the consolidation process that has sometimes been referred to as "secondary compression". (2) The structure is always degrading as plastic deformation proceeds even within the period of "secondary compression". (3) The decay of Overconsolidation to normal consolidation also proceeds with plastic deformation. In this sense, the degradation of structure can not be independent of the decay of Overconsolidation. However, since the decay of Overconsolidation is much faster than the degradation of structure in clay, then softening becomes possible with volume compression even under a considerably low stress ratio. Recovery of structure with time due to chemical bonding effects etc. in soil particles is beyond the scope of this study.
