• Geomechanics and Engineering
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• 제28권2호
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• pp.171-180
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• 2022

Time-dependent stress-strain behaviour significantly influences the compressibility characteristics of the clayey soil. In this paper, a series of oedometer tests were conducted in two loading patterns and investigated the time-dependent compressibility characteristics of Indian Montmorillonite Clay, also known as black cotton soil (BC) soil, during loading-unloading stages. The experimental data are analyzed using a new non-linear function of the Elasto-Visco-Plastic Model considering Swelling behaviour (EVPS model). From the experimental result, it is found that BC soil exhibits significant time-dependent behaviour during creep compared to the swelling stage. Pore water entrance restriction due to consolidated overburden pressure and decrease in cation hydrations are responsible factors. Apart from it, particle sliding is also evident during creep. The time-dependent parameters like strain limit, creep coefficient and C_αe/C_c are observed to be significant during the loading stage than the swelling stage. The relationship between creep coefficients and applied stresses is found to be nonlinear. The creep coefficient increases significantly up to 630 kPa-760 kPa (during reloading), and beyond it, the creep coefficient decreases continuously. Several parameters like loading duration, the magnitude of applied stress, loading history, and loading path have also influenced secondary compressibility characteristics. The time-dependent compressibility characteristics of BC soil are presented and discussed in detail.

• 콘크리트학회논문집
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• 제11권4호
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• pp.3-11
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• 1999

The creep characteristics of concrete under tensile stress has been usually assumed to have the same characteristics as that under compressive stress in the time-dependent analysis of concrete structures. However, it appears from the recent experimental studies that tensile creep behavior is much different from compressive one. In particular, high sustaining tensile stress may cause time-dependent cracking and thus lead to tensile failure. It is, therefore, necessary to model the tensile creep behavior accurately for realistic time-dependent analysis of concrete structures. The present paper to have been focused to suggested more realistic model for the tensile creep behavior of concrete. The models are compared with tensile creep test data available in the literature. The proposed model may allow more refined analysis of concrete structures under time-dependent loading.

• International Journal of Concrete Structures and Materials
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• 제18권3E호
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• pp.161-164
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• 2006

Cellulose fiber reinforced cement(CFRC) pipe has been gradually introduced in the pipe market as a replacement of previously popular asbestos cement pipes. Since CFRC pipe is still relatively unknown in the pipe market, there are great concerns for the design and application in practice related to the time-dependent behavior of CFRC under long-term sustained loading. This paper presents an experimental investigation of the time-dependent behavior of cellulose fiber reinforced cement(CFRC) pipe. A total of six CFRC pipes were tested under various loading levels, and their vertical deformation was recorded to understand the characteristics of the time-dependent behavior. Based on the test results, a factor of safety(FS) of 1.82 is proposed, and a regression factor(R) of 1.88 is estimated for the application of CFRC pipes in practice.

• 한국산학기술학회논문지
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• 제13권4호
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• pp.1895-1899
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• 2012

유한차분법을 적용한 압밀해석을 수행하였는데 순간하중이 재하되는 경우 유한차분법에 의해 예측되는 시간별 침하량과 Terzaghi 방법에 의한 침하량 사이의 차이는 시간격자간격을 충분히 작게 하여 해결할 수 있음을 알 수 있었다. 점증하중에 대한 압밀해석을 위한 유한차분식을 유도하였는데 해석결과에 따른 과잉간극수압의 분포가 Olson의 이론해와 일치하였다. 점증하중이 작용하는 경우에 대해 예측한 시간-침하거동에 있어 유도된 유한차분식에 의한 결과와 Terzaghi 및 Olson 에 의한 결과 또한 거의 일치하였다. 다단 점증하중에 대한 해석결과 또한 신뢰성이 높은 것으로 보인다.

• Structural Engineering and Mechanics
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• 제61권3호
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• pp.317-323
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• 2017

This work presents a new strategy to model stress dependent relaxation process in large deformation. The strategy is relied on the fact that in some particular soft materials undergoing large deformation, e.g., elastomers, rubbers and soft tissues, the relaxation time depends strongly on stress levels. To simplify the viscoelastic model, we consider that the relaxation time is the function of previous elastic deviatoric stress state experienced by materials during loading. Using the General Maxwell Model (GMM), we simulate numerically conditions with the constant and the stress dependent relaxation time for uniaxial tension and compression loading. Hence, it can be shown that the proposed model herein not only can represent different relaxation time for different stress level but also maintain the capability of the GMM to model hysteresis phenomena.

• Geomechanics and Engineering
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• 제7권3호
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• pp.279-295
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• 2014

A series of one-dimensional consolidation tests and triaxial creep tests were performed on Nansha clays, which are interactive marine and terrestrial deposits, to investigate their time-dependent behaviour. Based on experimental observations of oedometer tests, normally consolidated soils exhibit larger secondary compression than overconsolidated soils; the secondary consolidation coefficient ($C_{\alpha}$) generally gets the maximum value as load approaches the preconsolidation pressure. The postsurcharge secondary consolidation coefficient ($C_{\alpha}$') is significantly less than $C_{\alpha}$. The observed secondary compression behaviour is consistent with the $C_{\alpha}/C_c$ concept, regardless of surcharging. The $C_{\alpha}/C_c$ ratio is a constant that is applicable to the recompression and compression ranges. Compared with the stage-loading test, the single-loading oedometer test can evaluate the entire process of secondary compression; $C_{\alpha}$ varies significantly with time and is larger than the $C_{\alpha}$ obtained from the stage-loading test. Based on experimental observations of triaxial creep tests, the creep for the drained state differs from the creep for the undrained state. The behaviour can be predicted by a characteristic relationship among axial strain rate, deviator stress level and time.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 가을 학술발표회 논문집
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• pp.473-479
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• 1996

Until now, we assumed in the time-dependent analysis of concrete structure that tensile creep has same characteristics as compressive creep has. But, in according to results of researches, it appears that tensile creep is different from compressive creep in quantity and in mechanics because tensile creep is affected significantly by micro cracking. The test results indicate that the creep behavior of concrete in compression and tension is rather different. The test data shows that the amount of creep under tensile loading is larger than that under compressive loading. In this paper, a realistic tensile creep model is suggested and incorporated in the formulation. In order to get more accurate results of time-dependent analysis. The present study indicates that the long-term deflection of concrete structures under realistic tensile creep model is somewhat larger than that under ordinary compressive creep model.

• Geomechanics and Engineering
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• 제20권1호
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• pp.1-7
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• 2020

In structures excavated in rock mass, load progressively increases to a level and remains constant during the construction. Rocks display different elastic properties such as E_i and ʋ under different loading conditions and this requires to use the true values of elastic properties for the design of safe structures in rock. Also, rocks will undergo horizontal and vertical deformations depending on the amount of load applied. However, under constant loads, values of E_i and ʋ will vary in time and induce variations in the behavior of the rock mass. In some empirical equations in which deformation modulus of the rock mass is taken into consideration, elastic parameters of intact rock become functions in the equation. Hence, the use of time dependent elastic properties determined under constant loading will yield more reliable results than when only constant elastic properties are used. As well known, rock material will play an important role in the deformation mechanism since the discontinuities will be closed due to the load. In this study, E_i and ʋ values of intact rocks were investigated under different constant loads for certain rocks with high deformation capabilities. The results indicated significant time dependent variations in elastic properties under constant loading conditions. E_i value obtained from deformability test was found to be higher than the E_i value obtained from the constant loading test. This implies that when static values of elastic properties are used, the material is defined as more elastic than the rock material itself. In fact, E_i and ʋ values embedded in empirical equations are not static. Hence, this workattempts to emerge a new understanding in designing of safer structures in rock mass by numerical methods. The use of time-dependent values of E_i and ʋ under different constant loads will yield more accurate results in numerical modeling analysis.

• Geomechanics and Engineering
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• 제18권3호
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• pp.299-313
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• 2019

This research investigated the nonlinear compressibility, permeability, the yielding due to structural degradation and their effects on consolidation behavior of structured soft soils. Based on oedometer and hydraulic conductivity test results of natural and reconstituted soft clays, linear log (1+e) ~ $log\;{\sigma}^{\prime}$ and log (1+e) ~ $log\;k_v$ relationships were developed to capture the variations in compressibility and permeability, and the yield stress ratio (YSR) was introduced to characterize the soil structure of natural soft clay. Semi-analytical solutions for one-dimensional consolidation of soft clay under time-dependent loading incorporating the effects of soil nonlinearity and soil structure were proposed. The semi-analytical solutions were verified against field measurements of a well-documented test embankment and they can give better accuracy in prediction of excess pore pressure compared to the predictions using the existing analytical solutions. Additionally, parametric studies were conducted to analyze the effects of YSR, compression index (${\lambda}_r$ and ${\lambda}_c$), and permeability index (${\eta}_k$) on the consolidation behavior of structured soft clays. The magnitude of the difference between degree of consolidation based on excess pore pressure ($U_p$) and that based on strain ($U_s$) depends on YSR. The parameter ${\lambda}_c/{\eta}_k$ plays a significant role in predicting consolidation behavior.

• 한국지반신소재학회논문집
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• 제9권3호
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• pp.57-65
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• 2010

본 연구의 주된 목적은 반복적인 하중조건하에서 연성포장체의노반재료로써, EPS블럭의 시간의존적 변형을 연구하는데 있다. 반복하중 조건에서의 EPS블럭의 거동을 이해하기 위해서 본 연구에서는 실험적 방법 및 수치모형을 제시하였다. 이 수치모델링을 위해서 반복하중 조건하에서 관찰된 변형거동과 단위중량, 변형 그리고 적용된 하중과의 상관관계의 조사가 행해졌다. 실험결과는 핀들레이 이론과 반복하중 조건에서의 연구결과의 모델 분석등과 비교되었고, 보완된 핀들레이 모델과 본 연구에서 제시한 모델은 반복하중에서의 EPS블럭의 변형거동을 나타내는데 이용될 수 있는 것으로 기대된다.