• Title/Summary/Keyword: deformational modulus

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Evaluation of Deformational Characteristics of Railway Roadbeds subjected to Cyclic Load Using Various Testing Methods (다양한 시험기법을 이용한 반복하중을 받는 철도노반의 변형특성 평가)

  • Lee, Seong-Won;Kweon, Gi-Chul;Chung, Jae-Min;Hwang, Taik-Jean
    • Proceedings of the KSR Conference
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    • 2007.11a
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    • pp.1297-1302
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    • 2007
  • It is very important to evaluate the reliable deformational characteristics of soils not only in the analysis of geotechnical structures under working stress conditions as foundation in railroad or road system but also for the soil dynamic problems. Different testing techniques are likely to have different testing conditions as strain amplitude, stress level, loading frequency and number of loading cycles. The deformational characteristics of soils can be affected by these variables. In this paper, the effects on modulus of soils subjected to cyclic load were investigated. For the evaluation of deformational characteristics of soils subjected cyclic load, various testing such as TS, RC, TX, and FFRC tests were performed. It was shown that the modulus evaluated by various testing methods are comparable to each other fairly well when the effects of these factors were properly taken into account. For reliable evaluation, therefore, those effects on the modulus need to be considered, and measured values should be effectively adjusted to actual conditions where the soil is working.

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Development of whole Strain Range Constitutive Model Considering Deformational Characteristics of Subbase Materials in Korea (국내 보조기층 재료의 변형특성을 고려한 전체 변형률 영역의 구성모델 개발)

  • Kweon, Gi-Chul
    • International Journal of Highway Engineering
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    • v.6 no.3 s.21
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    • pp.65-77
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    • 2004
  • Deformational characteristics of subbase materials are important parameters in the mechanistic design of pavement. The subbase materials are mostly unbound granular materials in Korea, and seven representative subbase materials were collected for testing from the pavement construction sites. To evaluate the deformational characteristics of subbase materials, RC/TS, TX and FF-RC tests were performed. The effects of various variables on modulus were studied. The variation in the modulus with number of loading cycles and loading frequency are very small and can be ignored in a practical sense. The modulus of subbase materials were significantly affected by confining pressure and strain level. The representative modulus reduction curve and constitutive models for Korean subbase materials were suggested.

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Deformational Characteristics of Compacted Subgrade Soils in Korea with Specimen Construction Methods (시편 성형기법에 따른 국내 다짐 노상토의 변형특성)

  • Kweon, Gi-Chul;Hwang, Chang-Il
    • International Journal of Highway Engineering
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    • v.9 no.4
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    • pp.55-63
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    • 2007
  • Deformational characteristics of subgrade soils are important properties in the mechanistic analysis and design of pavement system. In this study, to evaluate the effect of specimen construction methods on deformational characteristics of subgrade soils in Korea, resonant column tests were performed for specimens constructed by various methods. Specimen construction method affected to the modulus value but the variation in the normalized modulus reduction curve was almost identical. The effects of specimen construction method on modulus are decreased with increasing confining pressure. The average maximum variation in the modulus value with different specimen construction methods was estimated as 16.8%. The differences in the modulus value of the specimens with same water content and dry density conditions that made by gyratory compaction and impact compaction were very small within 5.2%. The impact compaction method was proposed as a specimen construction method for determining the design input parameter testing considering that impact compaction method is much simpler and require less expensive specimen construction equipment and setup than gyratory compaction method.

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Correlation Model between Strength and stiffness characteristics for Subgrade Soils in Korea (국내 노상토의 강도 및 강성도 특성 상관모형)

  • Kweon, Gi-Chul;Jo, Jung-Nam;Hwang, Taik-Jean
    • International Journal of Highway Engineering
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    • v.11 no.4
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    • pp.17-23
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    • 2009
  • Deformational characteristics of subgrade soils are very important input parameters for pavement design. It is necessary to make an amount of effort to estimate experimentally the modulus of subgrade soils. In case of designing simple (or lower level) pavement section, the estimation of the modulus based on experiments must cause an excessive cost. It has proposed various empirical correlation models to estimate the modulus from basic properties of the materials or more simple alternative tests. Seven subgrade soils in Korea were tested in this study. It was founded that the deformational characteristics of subgrade soils in Korea has a close relation to strength characteristics, the empirical correlation model was proposed. There was a close relation between cohesion value and modulus at low confining stress ($r^2=0.93$). By comparing with the measured modulus and the modulus determined by proposed correlation model from strength characteristics, the value of the coefficient of determination ($r^2$) is 0.75.

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Effects of Water Content and Dry Unit Weight on Deformational Characteristics of Subgrade Soils (노상토의 변형특성에 대한 함수비 및 건조단위중량의 영향)

  • Kweon Gi-Chul;Oh Myeng-Joo
    • International Journal of Highway Engineering
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    • v.8 no.2 s.28
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    • pp.87-93
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    • 2006
  • To evaluate the deformational characteristics of subgrade soils, four subgrade samples in Korea were tested using the RC and TS tests with various dry unit weight and water content. Both the maximum modulus and normalized modulus reduction curves of subgrade soils were affected by the dry unit weight. The normalized modulus was decreased about 20% with increasing of relative compaction of 5%. It was founded that the variations of modulus of subgrade soils in Korea were over 40% with water content variation of $\pm$2%, and those effects can be estimated by exponential model. However, the normalized modulus reduction curves were almost identical and independent of water content. It was also founded that confining pressure, loading frequency, dry unit weight, and water content have an affect on modulus of subgrade soils independently. Therefore, it can be considered that those effects are independent variables.

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Evaluation of Nonlinear Deformational Characteristics of Soils from Laboratory and Field Tests (실내시험 및 현장시험을 통한 지반의 비선형 변형특성 평가)

  • 김동수;권기철
    • Geotechnical Engineering
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    • v.13 no.5
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    • pp.89-100
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    • 1997
  • It is very improtant to evaluate the reliable nonlinear deformational characteristics of soils not only in the analysis of geotechnical structures under working stress conditions but also for the soil dynamic problems. Field testings such as crosshole and pressuremeter tests can be used to determine the modulus of soils under in-situ conditions, but it is not possible to determine the modulus over the entire strain amplitude range. Laboratory methods such as resonant column 1 torsional shear test can be used to determine the modulus over the whole strain amplitude range, but it is very difficult to obtain the representative undisturbed samples on the sixte. For the reliable evaluation of nonlinear deformation characteristics of soils on a typical site, small strain modulus obtained from field testy and nomalized modulus reduction curve determined by laboratory bests need to be combined. In this paper, laboratory and Held testy were performed at a sixte which consisted of granite wearthered residual boils to evaluate the nonlinear deformational characteristics of coils such as the effects of strain amplitude, loading frequency, confining pressure and sample disturbance. It has been shorn that when the effects of these factors are properly taken into account, the stiffness values evaluated by various field and labrotary tests are comparable to each other fairly well. Finally, the procedure to evaluate the nonlinear deformstional characteristics of the sixte was proposed.

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Deformational Characteristics of Dry Sand Using Resonant Column / Torsional Shear Testing Equipment (공진주/비틂 전단(RC/TS)시험기를 이용한 건조 사질토의 변형특성)

  • 김동수
    • Geotechnical Engineering
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    • v.11 no.1
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    • pp.101-112
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    • 1995
  • Deformational characteristics of soils, often expressed in terms of shear modulus and material damping ratios, are important parameters in the design of soil-structure systems subjected to cyclic and dynamic loadings. In this paper, deformational characteristics of dry sand at small to intermediate strains were investigated using resonant column/torsional shear(RC 175) apparatus. Both resonant column(dynamic) and torsional shear (cyclic) tests were performed in a sequential series on the same specimen. With the modification of motion monitoring system, the elastic zone, where the stress strain relationship is independent of loading cycles and strain amplitude, was veri tied and hysteretic damping was found even in this zone. At strains above cyclic threshold, shear modulus increases and damping ratio decreases with increasing number of loading cycles. Moduli and damping ratios of dry sand are independent of loading frequency and values obtained from pseudostatic torsional shear tests are Identical with the values from the dynamic resonant column test, provided the effect of number of loading cycles is considered in the conlparison. Therefore, deformational characteristics determined by RC/TS tests may be applied in both dynamic and static analyses of soil-structure systems.

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Dynamic Deformation Characteristics of Korean Hydraulic-Fills Soil Deposits (국내 준설매립토 지반의 동적변형특성)

  • 김동수
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • 1999.04a
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    • pp.69-76
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    • 1999
  • Because of the limited land in Korea most of the projects require large-scale reclamation. The hydraulic-filled soil deposits are usually loose and susceptible to be liquified during earthquake. The dynamic deformation characteristics which expressed by shear modulus and damping ratio are important to analyze the earthquake ground motion. In this paper resonant column tests were performed on five hydraulic filled soil in Korea and the deformational characteristics at both small and medium strains were investigated. The coefficients in the Hardin equation to predict the representative maximum shear modulus and modulus reduction cure are also proposed.

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Measurement of Small-Strain Shear Modulus Using Pressuremeter Test (공내재하시험기를 이용한 미소변형 전단탄성계수 측정)

  • Kim, Dong-Su;Park, Jae-Yeong;Lee, Won-Taek
    • Geotechnical Engineering
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    • v.13 no.4
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    • pp.109-120
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    • 1997
  • In the working stress conditions, the strain level in a soil mass experienced by existing structures and during construction is less than about 0.1-1%. In order to analyse the deformational behavior accurately, the in-situ testing technique which provides the reliable deformational characteristics at small strains, needs to be developed. The purpose of this paper is to measure the small-strain shear modulus of soils by using pressuremeter test(PMT). PMT is a unique method for assessing directly the in-situ shear modulus of soils with strain amplitude. For the accurate small strain measurements without initial disturbance effect, the unloading-reloading cycle was used and the measured modulus was corrected in view of the relevant stress and strain levels around the PMT probe during testing. Not only in the calibration chamber but in the field, PMT tests were performed on the cohesionless soils. The variation in shear modulus with strain amplitude ranging from 10-2% to 0.5% was reliably determined by PMT PMT results were also compared with other in-situ and laboratory test results. Moduli obtained from different testing techniques matched very well if the effect of strain amplitude was considered in the com pall son.

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Alternative Method of Determining Resilient Modulus of Subbase Materials Using Free-Free Resonant Column Test (현장공진주시험을 이용한 보조기층 재료의 대체 $M_R$ 시험법)

  • Kweon, Gi-Cheol;Kim, Dong-Su
    • International Journal of Highway Engineering
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    • v.2 no.2
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    • pp.149-161
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    • 2000
  • The stiffness of the subbase materials is represented by the resilient modulus, $M_R$, which are very important properties in the mechanistic design of flexible pavement system. However, the cyclic $M_R$ testing method is too complex, expensive, and time consuming to be applicable on a production basis. In this study, the alternative $M_R$ testing technique for subbase materials was developed using a free-free resonant column (FF-RC) test considering deformational characteristics of subbase materials. To estimate the deformational characteristics of subbase materials, effects of strain amplitude and mean effective stress on modulus of subbase materials were investigated. The $M_R$ values determined by alternative testing procedures matched well with those determined by standard $M_R$ test, showing the capability of the proposed methods being used in determining $M_R$ values.

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