Study of the Validity of a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"><mml:mrow><mml:msubsup><mml:mi>σ</mml:mi><mml:mi>v</mml:mi><mml:mo>'</mml:mo></mml:msubsup><mml:mo>-</mml:mo><mml:msub><mml:mi>Ɛ</mml:mi><mml:mi>v</mml:mi></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mover accent="true"><mml:mi>Ɛ</mml:mi><mml:mo>.</mml:mo></mml:mover><mml:mi>v</mml:mi></mml:msub></mml:mrow></mml:math> Model in In Situ Conditions

Zhu

et al. 2014

Géotechnique Letters

Current studies rarely investigate the stress relaxation behaviour of soft soils. This paper proposes a practically useful coefficient with a formulation based on the behaviour of stress relaxation under onedimensional conditions. Firstly, the stress relaxation coefficient is proposed after summarising stress relaxation test results according to the linear relationship between the vertical stress and time in a double logarithmic plot. Secondly, from the newly developed rate-dependency based elastoviscoplastic formulations, an analytical solution for stress relaxation is derived. A unique relationship connecting the stress relaxation coefficient, the secondary compression coefficient and the ratedependency coefficient is then obtained. The applicability of the stress relaxation formulation with its key coefficient to determine time-dependent parameters is finally validated with published experimental results on reconstituted illite and Berthierville clay. Graham, 1989;Kutter & Sathialingam, 1992;Sheahan, 1995;Vermeer & Neher, 1999;Yin et al., 2010a;Wang & Yin, 2013 are conducted to evaluate the timedependent properties of soils. A few stress relaxation tests (e.g. Lacerda & Houston, 1973;Yin & Graham, 1989;Sheahan et al., 1994;Fodil et al., 1997;Kim & Leroueil, 2001;Yin & Hicher, 2008) have also been carried out and used to investigate the stress relaxation behaviour under different conditions. However, due to a lack of studies concerning the relationship between the key parameters of stress relaxation and strain-rate-dependency or creep parameters, the stress relaxation test is still not widely used to determine the timedependency related parameters of soft soils. This paper attempts to propose a stress relaxation coefficient with a formulation describing stress relaxation versus time, and investigates its relevance with the strainrate-dependency parameter and the secondary compression coefficient. First, studies on stress relaxation are briefly summarised and discussed. A new stress relaxation coefficient based on the stress relaxation oedometer test -one of the simplest tests for soils -is then proposed. By deriving a newly developed rate-dependency based formulation, a stress relaxation formulation is proposed and relationships connecting the stress relaxation coefficient, the secondary compression coefficient and the rate-dependency coefficient are obtained. Published experimental results on reconstituted illite and Berthierville clay are used to validate the proposed formulation and coefficient, and the relationships between different time-dependency parameters.

Section: Validation For Creep Behaviourmentioning

confidence: 99%

Stress relaxation coefficient and formulation for soft soils

Zhu

et al. 2014

Géotechnique Letters

“…for CRS oedometer tests on clays[1, 3,16,30]. A linear relationship between the strain-rate and the initial preconsolidation pressure in the plot log…”

Section: Proposed Strain-rate Based Modelmentioning

confidence: 99%

“…(i) A significant progressive loss of bonds develops during straining (by comparing the compression curves in the e-log ( ) v   plane for intact and remoulded samples [1][2][3][4][5][6][7][8]). …”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A one-dimensional strain-rate based model for soft structured clays

Sci. China Technol. Sci.

Wang

2011

The paper aims to investigate the destructuration effect on the time-dependent behaviour of soft structured clays. Viscosity coupled with destructuration is analysed based on experimental observations. A strain-rate based model is developed to describe the mechanical behaviour for both unstructured and structured clays under one-dimensional loading. The advantage of the proposed model lies in the determination of model parameters in a straightforward way, which leads to an easy use of the model for practical problems. Coupled with consolidation, the model is used to simulate oedometer tests at constant rate of strain and long-term creep oedometer tests on two structured clays. All comparisons between predicted and measured results demonstrate that the proposed model can reasonably describe the effect of destructuration on the time-dependent behaviour of soft structured clay under one-dimensional condition. Although the model is proposed for one-dimensional analysis, it can be a good base for developing a more general 3D model. structured clays, viscoplasticity, consolidation, creep, strain-rate, destructuration Citation: Yin Z Y, Wang J H. A one-dimensional strain-rate based model for soft structured clays. Sci China Tech Sci, 2012, 55: 90100,

“…It is considered that changes in volume under a constant eŠective stress are caused by the viscous behavior of the clay skeleton. According to many studies, it has been conˆrmed that such a viscous creep deformation not only takes place during secondary consolidation, but also during primary consolidation, i.e., when the eŠective stress levels are changing ( see Leroueil et al, 1985Leroueil et al, , 1988Imai and Tang, 1992;Imai et al, 2003;Tanaka, 2005b;Leroueil, 2006). To describe this viscous behavior, a strain-rate-dependent model, called the isotache model ( ½Suklje, 1957), is used.…”

Section: Introductionmentioning

confidence: 99%

Compressive Behavior During the Transition of Strain Rates

Tsutsumi

Tanaka

2011

Soils and Foundations

The application of a strain-rate-dependent model, for example, an isotache model, is very useful and highly eŠective for predicting the settlement due to consolidation, including secondary consolidation. In the isotache model, compression curves are not only determined by pressure, but also by strain rate. The validity of this model has been experimentally conˆrmed by many researchers using diŠerent types of oedometer tests, such as constant rate of strain (CRS) tests, incremental loading (IL) tests, etc. However, considerable scatter has been observed in the test results, which show the eŠects of the strain rate, and questions arise as to whether such scatter is caused by the heterogeneity of the soil samples or by the incompletion of the model. To avoid the heterogeneity of the tested samples, special CRS tests, in which the strain rate is not kept constant but is varied during the tests, were carried out on intact and reconstituted Osaka clay samples. The eŠects of the strain rate on the compressive behavior of these clays were carefully evaluated in terms of visco-plastic strain, assuming that the total strain consists of visco-plastic strain and elastic strain. It was conrmed that the stress and the visco-plastic strain relation of clay samples strongly depends on the visco-plastic strain rate. However, the eŠects of the strain rate, under a given constant visco-plastic strain rate, do not become constant when the visco-plastic strain rate becomes very small. The reason is assumed to be due to the development of structures under a constant small visco-plastic strain rate. The development of structures may restrict the applicability of the isotache model to the compressive behavior of clay.