• Geomechanics and Engineering
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• v.35 no.1
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• pp.55-65
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• 2023

Soft clay is widely spread in nature and encountered in geotechnical engineering applications. The creep property of soft clay greatly affects the long-term performance of its upper structures. Therefore, it is vital to establish a reasonable and practical creep constitutive model. In the study, two updated hyperbolic equations based on the volumetric creep and deviatoric creep are respectively proposed. Subsequently, three creep constitutive models based on different creep behavior, i.e., V-model (use volumetric creep equation), D-model (use deviatoric creep equation) and VD-model (use both volumetric and deviatoric creep equations) are developed and compared. From the aspect of prediction accuracy, both V-model and D-model show good agreements with experimental results, while the predictions of the VD-model are smaller than the experimental results. In terms of the parametric sensitivity, D-model and VD-model are lower sensitive to parameter M (the slope of the critical state line) than V-model. Therefore, the D-model which is developed by incorporating the updated deviatoric creep equation is suggested in engineering applications.

• Geomechanics and Engineering
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• v.29 no.6
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• pp.615-626
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• 2022

The soft clays are widely distributed, and one of the prominent engineering problems is the creep behavior. In order to predict the creep deformation of soft clays in an easier and more acceptable way, a simple creep constitutive model has been proposed in this paper. Firstly, the triaxial creep test data indicated that, the strain-time (𝜀-t) curve showing in the 𝜀-lgt space can be divided into two lines with different slopes, and the time referring to the demarcation point is named as t_EOP. Thereafter, the strain increments occurred after the time t_EOP are totally assumed to be the creep components, and the elastic and plastic strains had occurred before t_EOP. A hyperbolic equation expressing the relationship between creep volumetric strain, stress and time is proposed, with several triaxial creep test data of soft clays verifying the applicability. Additionally, the creep flow law is suggested to be similar with the plastic flow law of the modified Cam-Clay model, and the proposed volumetric strain equation is used to deduced the scaling factor for creep strains. Therefore, a creep constitutive model is thereby established, and verified by successfully predicting the creep principal strains of triaxial specimens.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.465-472
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• 2003

Creep Poisson's ratio reported by previous experimental studies on multiaxial creep of concrete was controversial. The Poisson's ratio is very sensitive to small experimental error that is inevitably induced, and the sensitivity may cause the controversy. It is difficulty to find out the properties on multiaxial creep of concrete. Therefore, a new approach method to analyze the test results is needed to precisely understand the properties on multiaxial creep of concrete. In this study, microplane model is used as a new approach method in analyzing the multiaxial creep test data. The six data sets extracted from the literature are fitted from regression analysis. Double-power law as a model representing volumetric and deviatoric creep evolutions on microplane is used, and six parameters in volumetric and deviatoric compliances are determined on the assumption that the volumetric and deviatoric creep strains are linearly proportional to corresponding stresses. The optimum fits give very accurate description of the test data. The Poisson's ratio calculated from the optimum fits varies with time and does not depends on the stress states, namely, uniaxial, biaxial, and triaxial stress states. Regression analysis is also performed on the assumption that the Poisson's ratio remains constant with titre. The constant Poisson's ratio can be use in practice without serious error.

• Geotechnical Engineering
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• v.14 no.5
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• pp.129-142
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• 1998

This research is focused on the inducement of the constitutive equation considering the creep strain component and on the development of a finite element method program. The purpose of this research was to contribute to the design of construction structures or to the construction management in soft clay ground through predicting the long-term strain of construction structures reasonably bused on the above program. Modified Cam Clay model was adopted to describe the elastic-plastic behavior of clayey soil. And in the calculation of the creep sprain, the secondary coefficient of consolidation C. was applied for considering the volumetric creep element and the constants m, $\alpha$, A were rosed by the empirical creep equation proposed by Singh 8E Mitchell for considering the deviatoric creep element. To examine the reliability of the program which is developed in this study, the estimated values by this program were compared with the theoretical solution and the experimental results. And the applicability of the developed program was found to be reliable from the sensitive analysis of each parameters used in this study. According to the results obtained from the application of the program on the field measurement data, the estimated values by the program were found with be consistent with the actual values. And from the analysis of the displacement of embankments, the case of considering the creep behavior induced much fower errors than the case of neglecting it. But the results obtained from considering the volumetric creep behavior only were slightly underestimated the results from considering the deviator creep behavior showed the slightly overestimated values. Therefore, it remains the task of further studios to develop the laboratory test devices to obtain the reliable creep parameters, and to select the appropriate soil parameters, etc.

• Journal of the Korea Concrete Institute
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• v.16 no.2 s.80
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• pp.185-194
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• 2004

It is difficult to analyze and predict the long-term behavior of concrete structures and members under multiaxial stresses because most of existing researches on creep of concrete were mainly concerned about uniaxial stress state. Therefore, the main objective of this paper is the investigation of creep properties of concrete under multiaxial stresses. This paper presents experimental study on creep of concrete under multiaxial compression. Twenty seven cubic specimens($20{\times}20{\times}20 cm$) for three concrete mixes were tested under uniaxial, biaxial, and triaxial stress states. Creep strains were measured in three directions of principal stresses. Poisson's ratio at the initial loading was obtained, as was Poisson's ratio due to creep stain and Poisson's ratio due to the combined creep strain and elastic strain. These Poisson's ratios were approximately equal for each concrete mix. The Poisson's ratio at the initial loading and the Poisson's ratio for the combined strain Increased slightly as the strength of the concrete increased. In addition, the volumetric creep strain and deviatoric creep strain were linearly proportional to volumetric stress and deviatoric stress, respectively.

• Journal of the Korea Concrete Institute
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• v.16 no.2 s.80
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• pp.195-204
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• 2004

Poisson's ratio due to multiaxial creep of concrete reported by existing experimental works was controversial. Poisson's ratio calculated from measured strain is very sensitive to small experimental error. This sensitivity make it difficult to find out whether the Poisson's ratio varies with time or remain constant, and whether the Poisson's ratio has different value with stress states or not. A new approach method is needed to resolve the discrepancy and obtain reliable results. This paper presents analytical study on multiaxial creep test results. Microplane model as a new approach method is applied to optimally fitting the test data extracted from experimental studies on multiaxial creep of concrete. Double-power law is used as a model to present volumetric and deviatoric creep evolutions on a microplane. Six parameters representing the volumetric and deviatoric compliance functions are determined from regression analysis and the optimum fits accurately describe the test data. Poisson's ratio is calculated from the optimum fits and its value varies with time. Regression analysis is also performed assuming that Poisson's ratio remains constant with time. Four parameters are determined for this condition, and the error between the optimum fits and the test data is slightly larger than that for six parameter regression results. The constant Poisson's ratio with time is obtained from four parameter analysis results and the constant value can be used in practice without serious error.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.195-200
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• 2006

Laboratory creep experiments show that compaction of unconsolidated shale is an irrecoverable process caused by viscous time-dependent deformation. Using Perzyna's viscoplasticity framework combined with the modified Cam-clay theory, we found the constitutive equation expressed in the form of strain rate as a power law function of the ratio between the sizes of dynamic and static yield surfaces. We derived the volumetric creep strain at a constant hydrostatic pressure level as a logarithmic function of time, which is in good agreement with experimental results. The determined material constants indicate that the yield stress of the shale increases by 6% as strain rate rises by an order of magnitude. This demonstrates that the laboratory-based prediction of yield stress (and porosity) may result in a significant error in estimating the properties in situ.

• Computers and Concrete
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• v.33 no.4
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• pp.349-359
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• 2024

This study aims to investigate the effect of restraint configuration on crack formation due to shrinkage-and-creep-induced volumetric change in unbonded post-tensioned slabs. The first part of this study focuses on the comparison of existing shrinkage and creep calculation models that are used to predict the volume-changing behavior of concrete. The second part of this study presents the finite element analysis of a series of architectural configuration prototypes subjected to shrinkage and creep, which comprise unbonded post-tensioned slabs with various restraint configurations. The shrinkage and creep effects were simulated in the analysis by imposing strains obtained from one selected calculation model. The results suggest that a slab up to 300 ft. (90 m) in length does not require a closure strip if it is unrestrained by perimeter walls, and that the most effective restraint crack mitigation strategy for a slab restrained by perimeter walls is a partial wall release.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09b
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• pp.131-137
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• 2010

`Frost heave' is volumetric extension behavior of soil due to freezing. It could have a bad effect to foundations of infrastructures like building, road, railroad and bridge. Therefore, it is considered as a primary design parameter with 'adfreeze bond' and 'creep deformation' for foundation design in cold region. In some countries, studies for analyzing frost heave in many ways have being performed, however, only a few studies for evaluating frost susceptibility of soils by measuring frost heave rate of frozen soils in Korea. For analyzing frost heave as a foundation design parameter, both frost heaving rate and heaving pressure are should be addressed in study. Hence, in this study, development of experimental apparatus to evaluate frost heave and pressure is suggested.