Research on the small strain stiffness behavior of soft clay under complex stress path

The traditional state-surface approach to the study of unsaturated soil behavior is becoming much less popular these days, as it uses unique constitutive surfaces to represent unsaturated soil behavior. This approach is essentially a nonlinear elastic formation and cannot be used to explain complex stress-path dependency for unsaturated soils. In this paper, a modified state-surface approach (MSSA) is proposed to represent unsaturated soil behavior under isotropic stress conditions in which a conventional void-ratio state surface is considered to be made up of an elastic surface and a plastic hardening surface. The plastic hardening surface remains stationary at all times, whereas the elastic surface remains unchanged when the soil experiences elastic deformation and moves downward when there is plastic hardening occurrence. Using the MSSA, the loading–collapse (LC) and the suction increase (SI) yield curves in the Barcelona basic model (BBM) are derived. The prediction of three typical cases of soils under isotropic conditions and experimental results using the proposed approach confirmed its feasibility, simplicity, and potential for the study of unsaturated soil behavior.

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The Studies of Rock Damage Softening Statistical Constitutive Model under True Triaxial Stress State

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.580-583.312 ◽

2014 ◽

Vol 580-583 ◽

pp. 312-315

Author(s):

Hui Mei Zhang ◽

Xiang Miao Xie ◽

Geng She Yang

Keyword(s):

Constitutive Model ◽

Strain Curve ◽

Stress Path ◽

Complex Stress ◽

Model Parameters ◽

Stress Strain ◽

Deformation And Failure ◽

True Triaxial ◽

Complex Stress Path ◽

The Impact

From the feature of rock micro-unit failure obeys Poisson random distribution, the damage softening statistical constitutive of was established under true triaxial confinement based on D-P criterion, so the impact of the intermediate principal stress on rock deformation and failure was considered in theory, and the actual engineering rock complex stress path evolution was reflected more realistically. Furthermore, according to the geometrical conditions of stress-strain relationship, the theoretical relationship between constitutive model parameters and the stress-strain curve characteristic parameters during the process of rock softening and deforming, which enhance the adaptability of the model. Finally, the rationality of the model verified by the measured data.

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Analysis of Nonlinear Stress and Strain in Clay under the Undrained Condition

Journal of Mechanics ◽

10.1017/jmech.2011.24 ◽

2011 ◽

Vol 27 (2) ◽

pp. 201-213 ◽

Cited By ~ 6

Author(s):

P.-G. Hsieh ◽

C.-Y. Ou

Keyword(s):

Soft Clay ◽

Stress Path ◽

Small Strain ◽

Model Parameters ◽

Soil Behavior ◽

Total Stress ◽

Soil Stiffness ◽

Nonlinear Stress ◽

Strength Tests ◽

Laboratory Stress

ABSTRACTThough the total stress undrained analysis approach in geotechnical engineering is widely utilized by practicing engineers, it has some intrinsic imperfections that cause the obtained parameters to have unavoidable empirical correlations. In this study, an undrained soft clay model is developed, which overcomes the imperfections of the conventional total stress undrained approach. In addition, the high soil stiffness at small strain and the concept of yield surface are employed to realistically simulate actual soil behavior. The model parameters can be obtainable directly from conventional laboratory tests. The model is validated through different laboratory stress path tests and strength tests in this paper.

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Small Strain Stiffness of Artificially Cemented Soft Clay: Modelling the Effect of Structure Degradation

E3S Web of Conferences ◽

10.1051/e3sconf/20199211009 ◽

2019 ◽

Vol 92 ◽

pp. 11009

Author(s):

Qasim Khan ◽

Yannick Ng ◽

Taeseo Ku

Keyword(s):

Soft Clay ◽

Small Strain ◽

Kaolin Clay ◽

Bender Elements ◽

Confining Stress ◽

Soft Clays ◽

Small Strain Stiffness ◽

Structure Degradation ◽

Before And After ◽

Vertically Aligned

This paper presents a study on the evolution of small strain stiffness (Gmax) along vertical and horizontal directions for lightly cemented clay. Soft clays have historically been a subject for studying the evolution of stiffness anisotropy under varying loading conditions. These studies have focused on stress history (overconsolidation) effects as well. However, for lightly cemented clays, such studies are limited and their main scope has primarily been on the evolution of vertically aligned stiffness (GVH) at varying effective confining stresses. This study investigates the effect of isotropic loading on uncemented and lightly cemented kaolin clay. Kaolin clay mixed with 10% cement is used in this study. Stiffness measurements have been conducted using bender elements for obtaining GVH and GHH hence resulting in the measurement of vertical and horizontal stiffness values respectively. By comparing the behaviour of both samples, the influence of bonding and fabric due to cementation on the evolution of stiffness and anisotropy is studied. In order to characterize the behavior of structure in cemented soil with confining stress, a modelling equation is applied for the cemented sample to predict the variation of Gmax before and after yielding.

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Effects of stress paths on the small-strain stiffness of completely decomposed granite

Canadian Geotechnical Journal ◽

10.1139/t05-009 ◽

2005 ◽

Vol 42 (4) ◽

pp. 1200-1211 ◽

Cited By ~ 10

Author(s):

Y. Wang ◽

C WW Ng

Keyword(s):

Shear Strain ◽

Shear Stiffness ◽

Stress Path ◽

Small Strain ◽

Bender Elements ◽

Small Strain Stiffness ◽

Small Strains ◽

Average Shear ◽

Decomposed Granite ◽

Completely Decomposed Granite

Research on the small-strain (0.001%1%) characteristics of sedimentary soils and sands has advanced to the stage where it has been utilized in engineering analysis and design for some time. Despite the progress, the stiffness characteristics of weathered materials such as completely decomposed granite (CDG) at small strains have still attracted relatively little research attention. This paper describes a systematic laboratory investigation of the small-strain characteristics of intact CDG subjected to various triaxial stress paths, including drained compression and extension tests. The small-strain stiffness was measured using bender elements and internal local transducers. Measurements from bender elements illustrate that the elastic shear modulus of CDG increases as the mean effective stress increases and the void ratio decreases. Significant nonlinear shear stiffness shear strain and bulk modulus volumetric strain relationships were observed. At 0.01% shear strain, the measured average shear stiffness obtained from the extension tests was about 60% higher than that from the compression tests. The average shear stiffness for the tests with a 90° rotation of the stress path was about 50%70% higher than that of tests without a change in the direction of the stress path after saturation.Key words: completely decomposed granite, nonlinearity, small strains, extension, compression, recent stress history.

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Small-strain stiffness of Zenoz kaolin in unsaturated conditions

Canadian Geotechnical Journal ◽

10.1139/t11-105 ◽

2012 ◽

Vol 49 (3) ◽

pp. 311-322 ◽

Cited By ~ 15

Author(s):

Mahnoosh Biglari ◽

Anna d’Onofrio ◽

Claudio Mancuso ◽

Mohammad Kazem Jafari ◽

Ali Shafiee ◽

...

Keyword(s):

Shear Stiffness ◽

Stress Path ◽

Small Strain ◽

Complex Stress ◽

Resonant Column ◽

Wetting And Drying ◽

Isotropic Compression ◽

Remarkable Effect ◽

Constant Suction

An experimental study has been carried out to investigate the effects of isotropic compression, wetting, and drying on the initial shear stiffness of Zenoz kaolin, an unsaturated lean clay, both in normally consolidated and overconsolidated conditions. The proposed study was conducted using fixed–free resonant column – torsional shear (RCTS). Specimens were compacted using the undercompaction technique. Initial shear stiffness was measured almost continuously along complex stress paths including (i) an initial equalization stage to a suction value of 0, 50, 150, and 300 kPa; (ii) an isotropic compression stage at constant suction, up to a net stress high enough to move the loading collapse line; (iii) an isotropic unloading stage at constant suction; (iv) a wetting and (or) drying path. The mentioned stress path allowed elimination or determination of the overconsolidation effect on the initial shear stiffness measured. The behavior observed is qualitatively similar to that of saturated soil, while wetting data clearly indicate that G0 depends significantly on volumetric behavior. In normally consolidated samples where wetting is accompanied by collapse, reduction in suction has no remarkable effect on G0. Conversely, in overconsolidated samples G0 reduces significantly as suction decreases.

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Simplified analyses of stress induced anisotropy in remolded soft clay under undrained conditions

Archives of Materials Science and Engineering ◽

10.5604/01.3001.0014.5762 ◽

2020 ◽

Vol 2 (105) ◽

pp. 56-64

Author(s):

P. Lin ◽

Z.-x. Li ◽

A. Garg ◽

J.S. Yadav

Keyword(s):

Soft Clay ◽

Constitutive Models ◽

Stress Path ◽

Complex Stress ◽

Triaxial Tests ◽

Induced Anisotropy ◽

Stress Induced Anisotropy ◽

Undrained Conditions ◽

Plain Strain ◽

Properties Of Soil

Purpose: The soil’s anisotropy induced by stress (i.e. stress induced anisotropy) has an important effect on the behavior of soil. This paper focuses on analyzing the anisotropy of remolded Shantou soft clay under compression stress path. Design/methodology/approach: Experiments were executed by using three axle experimental instruments. The data obtained from the plain strain tests were analyzed and the relationship between stress and strain was calculated by using the modified Duncan- Chang and Lade-Duncan models. The models were modified under the condition of plain strain and cohesion. Findings: It was concluded that in complex stress path conditions, the conventional triaxial tests may not fully reflect the actual stress of soil and its response in the Duncan-Chang and Lade-Duncan models. Research limitations/implications: The formulation of Mohr-Coulomb failure criterion in the plasticity framework is quite diffcult. As a result, dilatancy cannot be described. The properties of soil in unload or drained conditions remain to be part of further investigated. Practical implications: Based upon the two stiffness parameters, the modified Duncan- Chang model has captured the soil behaviour in a very conformable way and is recommened for practical modeling. These constitutive models of soil are widely used in the numerical analyses of soil structure such as embankments. Originality/value: Duncan-Chang and Lade-Duncan models widely used in engineering practices are modes based on conventional triaxial cases. Both models have have some inherent limitations to represent the stress-strain characteristics of soils, such as shear-induced dilatancy and stress path dependency and required corrections. In this investigation, the tests are carried out in undrained conditions. It is related to the properties of soil in load conditions.

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