• 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.

• Geotechnical Engineering
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• v.9 no.1
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• pp.21-30
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• 1993

To know the importance of soil paramters which are used to estimate the deformation and porepressure of soil, the sensitivity for soil parameters in elastic analysis is analyzed. Using the consolidation teat results of several cohesive soils, soil parameters are estimated by back analysis method, and from the parameters the deformations and porepressures of the soil are estimated by elastic analysis, In elastic analysis for soil-deformation and porepressure, the sensitivity for the Young's modulus is large, and the esimation of Young's modulus is more important in pro- portion to the size of stress. Using the measured results during initial short period in small stress, the soil parameters can be correctly estimated by back analysis method. To decrease the iteration number in back analysis and to get the better paramters, the initial measurements in more nodes are required and the more accurate initial measurements are required.

• Journal of Korean Society of Steel Construction
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• v.15 no.2
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• pp.137-145
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• 2003

In this study, direct tensile fatigue tests of the PS bar were performed in terms of diameter, minimum stress level, and maximum stress level. In the static test, the stress - strain curve and ultimate streng th of the PS bar were determined. Results of the fatigue test indicate that the diameter of the PS bar was not influenced by fatigue life. Minimum stress also had quite an influence on the fatigue of the PS bar. Thus, the fatigue characteristic equation was proposed in terms of stress range and minimum stress through statistical process. Strains on specimen that loaded direct tension were measured in the fatigue test, with the secant modulus of elasticity calculated from measured strains. The strain development consisted of three different stages, i.e., rapid increases during the initial fatigue life, uniform increases during the middle stage, and rapid increases until failure. The secant modulus of elasticity decreased during the fatigue life with increasing strain. However, stress level seemed to have no influence on the secant modulus of elasticity.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.3
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• pp.159-168
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• 2012

본 연구에서는 해성 점성토에 대하여 반복 삼축시험을 실시하고 응력-변형률 관계 및 유효응력경로 특성 분석을 통해 동적 변형 및 강도 특성을 조사하였다. 시험에 사용된 시료는 일본 도쿠시마현의 코마츠시마 항 인근에서 채취된 점성토이며, 반복 삼축시험으로 동적 비배수 삼축시험, 동적 비배수 삼축시험 후 동적 삼축변형시험, 다단계 동적 비배수 삼축시험, 동적 삼축 변형시험 등 4종류의 시험을 수행하고, 시험 주파수로서 0.1 및 0.01 Hz을 적용하였다. 본 연구 결과 0.01 Hz로 수행된 동적 삼축시험 결과는 0.1 Hz로 수행된 삼축시험 결과보다 평균유효응력의 감소량이 크며, 반복 하중은 해성 점성토의 구조적 약화를 초래하고 초기 거동시 발생하는 간극수압과 밀접하게 관련이 있는 것으로 나타났다. 또한 미소변형률 영역에서 등가 탄성계수는 시험 횟수가 증가함에 따라 점차 감소하며, 감쇠비는 점차 증가하는 것으로 보아 변형계수는 반복 하중으로 인한 전단변형률의 축척에 따른 변형률 의존 거동에 관련하는 것으로 판단된다.

• Journal of the Korean Geotechnical Society
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• v.21 no.6
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• pp.67-79
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• 2005

The field plate load test has a good potential for determining modulus since it measures both plate pressure and settlement. Conventionally the modulus has been assumed to be a constant secant value defined from the settlement of the plate at a given load intensity. A constant modulus (modulus of subgrade reaction, k), however, may not be a representative value of subgrade soil under working load. Field strain(o. stress)-dependent modulus characteristics of subgrade soils, at relatively low to intermediate strains, are important in the pavement design. In this study, the field strain dependent moduli of subgrade soils were obtained using cyclic plate load test. Testing procedure and data reduction method are proposed. The field crosshole and laboratory resonant column tests were also performed to determine field nonlinear modulus at $0.001\%\;to\;0.1\%$ strains, and the modulus values and nonlinear trends are compared to those obtained by cyclic plate load tests. Both modulus values match relatively well when the different state of stress between two tests was considered, and the applicability of field cyclic plate load test for determining nonlinear modulus values of subgrade soils is verified.

• Journal of the Korean Geotechnical Society
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• v.15 no.1
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• pp.175-183
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• 1999

Recently, problems related to vibrations of decomposed granite soils have acquired increasing attention in Korea because those soils cover approximately one third of the country. Both resonant column and cyclic triaxial test were performed to investigate deformation characteristics of unsaturated and cement-mixed decomposed granite soils in Suwon region. The important soil parameters in this respect are the shear moduli, dynamic moduli of elasticity and damping ratios. The dynamic parameters are influenced by variables such as strain amplitude, ratio of loading cycles, and degree of saturations, etc. Test results and data have shown that the optimum degree of saturation to the maximum shear modulus due to a capillary menisci effect was about 17~18 % at low strain amplitude and 10~15 % at intermediate strain amplitude. This paper suggests the range of threshold strain and mean shear modulus of decomposed granite soils in Suwon region. It also proposed the empirical relationship between the dynamic parameters for cement-mixed and non-mixed decomposed granite soils.

• Geotechnical Engineering
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• v.8 no.1
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• pp.19-28
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• 1992

Recently, testing equipment which can run resonant column test altogether with the torsional shear test at the very highly controlled condition was developed at the University of Texas at Austin(U.S.A). With this equipment, the effects of high amplitude pre-straining vibrations on the dynamic properties of clean sands were studied. Tests showed the following results. Low amplitude shear modulus was gradually increased with little void ratio change as the number of high amplitude vibration cycles increased. Variation of volumetric strain with confining pressure for the pre -strained specimen under vibration was smaller than that of fresh specimen. Also the slope of the diagram for shear modulus and confining pressure relationship of the prestrained specimen was smaller than that of fresh specimens. These results agreed well with the analytical results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.574-577
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• 2007

본 논문에서는 실 시공 중인 PSC 교량에 대하여 풍하중에 의한 상시 진동 계측 자료을 기반으로, 교량의 동특성(고유진동수, 모드형상)을 추정하였으며, 이를 바탕으로 대상 교량의 탄성계수를 추정하여 정적 계측을 통한 탄성계수 결과와 비교하였다. 본 논문에서 사용한 동특성 추정 기법은, 대표적인 주파수 영역 해석 방법인 Frequency Domain Decomposition(FDD) 방법과 시간영역 해석 방법인 Stochastic Subspace Identification(SSI) 방법을 이용하였다. 탄성계수 추정은 유한요소모델과 계측 결과를 이용하여 두 개의 결과 차이가 수렴하도록 하는 반복 계산을 통해 탄성계수를 추정하였다. 우선, 탄성계수 추정 기법의 검증을 위해, 수치 해석을 통하여 그 기법을 검증하였으며, 해석 결과 정확한 탄성계수값을 추정하였으며, 이를 통해 본 논문에서 적용한 탄성계수 추정법에 대한 신뢰도를 확인하였다. 이를 바탕으로 사용된 추정 기법을 실 교량에 적용하기 위해 실제 상시 진동 계측 값을 바탕으로 실교량의 동특성 및 탄성계수를 추정하였다. FDD 및 SSI 기법을 통한 모드 해석 결과, 두 기법 모두 유사한 결과를 나타내어 FDD 및 SSI 두 방법에 대한 결과의 신뢰도를 확인 할 수 있었다. 추정 탄성계수 값은 거더 단면내 설치한 응력계 및 변형률계를 통한 계측 결과값의 범위 내에 있음을 확인하였다. 따라서 본 논문에서 적용한 교량의 상시 진동 데이터를 바탕으로 한동특성 및 탄성계수 추정법이 구조물의 대략적인 탄성계수 및 이에 따른 구조물의 전체적인 건전도를 파악하는데 도움이 되리라 생각된다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.4
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• pp.469-476
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• 2023

Soil plasticity models for cyclic and dynamic loads are essential in non-linear numerical analysis of geotechnical structures. While a single yield surface model shows a linear behavior for cyclic loads, J₂-bounding surface plasticity model with zero elastic region can effectively simulate a nonlinearity of the ground response with the same material properties. The radius of the yield surface inside the boundary surface converged to 0 to make the elastic region disappear, and plastic hardening modulus and dilatancy define plastic strain increment. This paper presents the stress-strain incremental equation of the developed model, and derives plastic hardening modulus for the hyperbolic model. The comparative analyses of the triaxial compression test and the shallow foundation under the cyclic load can show stable numerical convergence, consistency with the theoretical solution, and hysteresis behavior. In addition, plastic hardening modulus for the modified hyperbolic function is presented, and a methodology to estimate model variables conforming 1D equivalent linear model is proposed for numerical modeling of the multi-dimensional behavior of the ground.

• International Journal of Highway Engineering
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• v.10 no.1
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• pp.63-74
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• 2008

Resilient deformation characteristics on unbound pavement materials have been adopted for design and nonlinear analysis of pavement structure under traffic loadings. However, relatively few studies have been done on the nonlinear resilient behavior of unbound pavement materials in Korea. In addition, only the limited information is available for estimating the resilient modulus values on unbound materials. In this study, a laboratory resilient-deformation test under repeated loadings is performed in order to fud a proper constitutive model that correlates the resilient modulus with stress state from field condition. Finally, a finite element analysis is conducted for evaluating the nonlinear characteristics of unbound materials. and the pavement performance respectively.