• International Journal of Highway Engineering
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• v.13 no.1
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• pp.33-40
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• 2011

The resilient modulus which is presented mechanical properties of compacted subbase material is the design parameter on the Mechanistic - Empirical pavement design guide. The compaction control method on the Mechanistic - Empirical pavement design guide will be the way to confirm whether the in-situ elastic modulus measured after the compaction meets the resilient modulus which is applied the design. The resilient modulus in this study is calculated by the neural network suggested by Korea Pavement Research Program, and degree of compaction as the existing compaction control test and plate bearing capacity test(PBT) was performed to confirm whether the in-situ elastic modulus is measured. The Light Falling Weight Deflectometer(LFWD) is additionally tested for correlation analysis between each in-situ elastic modulus and resilient modulus, and is proposed correlation equation and test interval which can reduced overall testing cost. Also, the subbase compaction control procedure based on the in-situ elastic modulus is proposed using the in-situ PBT and LFWD test result.

• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.827-838
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• 1994

Numerous pavement response models rely on constitutive relationships to describe the response of granular materials. In this study, a nonlinear elastic constitutive model which is a function of bulk stress and octahedral shear stress is proposed to describe the resilient behavior of thick granular base courses under flexible airfield pavements. Special features of this model are its accuracy to predict the nonlinear resilient behavior, its simplicity to determine the material constants and its ability to model the secondary effect of decreasing the resilient modulus due to shear effects. In laboratory tests, the nonlinear resilient behavior of granular materials is investigated and values of resilient moduli are determined to provide data for verifying the proposed model. It is found that the resilient modulus is much more dependent on the states of stresses in terms of bulk stress and deviator stress than any other factors. Result of comparison shows that predicted values of resilient moduli are in good agreement with the measured values indicating that the proposed model is suitable to describe the nonlinear resilient behavior of the granular material with wide range of stress states which meet in airfield pavements.

• Journal of the Korean Society of Groundwater Environment
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• v.7 no.1
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• pp.20-23
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• 2000

A general solution for determining the storage coefficient from multi-step pumping test recovery data is suggested. This solution is essentially based on the method of Banton and Bangoy (1996), which used single-step pumping test recovery data. The suggested solution can be applied to any-step pumping test recovery data. We have demonstrated the applicability of the general solution to single-, double-, and triple-step pumping and/or step-drawdown test data partially described in Lee and Lee (1999). The estimates of storage coefficient as well as transmissivity are well consistent with the values from other methods for pumping phase data.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.1
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• pp.229-236
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• 2015

In this study, the resilient modulus test and Light Weight Deflectormeter (LWD) test were conducted to simulate the moving vehicle load for the evaluation of the internal failure of epoxy asphalt pavement. The Measured displacement in the resilient modulus test of epoxy asphalt concrete showed very little residual deformation under repeated loads unlike the conventional asphalt. Therefore, the test results were evaluated as a normal state due to its similarity with elastic deformation. The deflection results from the resilient modulus tests were converted to the surface deflection modulus and the normal range of surface deflection modulus was estimated applying LWD measurement of 1 SIGMA level. Internal failure of pavements were estimated using the suspicious failure range at $60^{\circ}C$ and hysteresis. Internal moisture penetration and a decrease in bonding were observed in partial areas at $140{\mu}m$ of surface deflection. However, the areas showed inflection points in the hysteresis. Field investigation by suggested criterion indicated a high degree of accuracy.

• International Journal of Highway Engineering
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• v.14 no.3
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• pp.49-58
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• 2012

In many countries including Korea, the design concept of pavement structure has been converted from empirical method to mechanisticempirical method since the advent of compaction control based on resilient modulus proposed by AASHTO in 1986. Studies of last decades indicates that the classical compaction control method based on relative compaction and plate bearing test(PBT) will necessarily move to the methods taking advantage of light falling weight deflectometer(LFWD) and dynamic cone penetrometer(DCP) in addition to PBT. In this study, the validity of resilient modulus prediction equation proposed by Korean Pavement Design Guide is verified by comparison with physical properties of subgrade soil and the results of structural analysis. In addition, correlational equations between elastic modulus measured by various field tests and resilient modulus estimated by empirical model are proposed. Finally, a field test-based compaction control procedure for subgrade is suggested by using proposed correlational equations.

• Journal of Digital Convergence
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• v.11 no.12
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• pp.639-647
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• 2013

This paper is a methodological research aimed at developing a mental disorder recovery scale (MDRS) and testing its validity and reliability. After three sessions of factor analysis, a total of three factors using an Eigen value of 1.0 or more were drawn. The explanatory power was found to be 58.1%. All the items met the criteria for communality and factor loading with no item removed, and, ultimately, 25 items were selected. Criterion-related validity test showed that Pearson's correlation coefficient was significant at .71 (p<.01) with significant correlation with each factor (p<.01). The reliability test showed that Cronbach's ${\alpha}$ coefficient was .95 and that Cronbach's ${\alpha}$ coefficient for each factor ranged from .87 to .93. MDRS, which was developed in this study and possessing 3 factors and 25 items, had both its validity and reliability confirmed; therefore, the developed scale would be useful to evaluate the recovery of individuals with mental disorder.

• Journal of the Korean Society for Railway
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• v.11 no.3
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• pp.257-262
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• 2008

Design and analysis of road subgrade system, which is exposed to repetitive loading condition, uses resilient modulus. The behavior of railway subgrade system will not be quite different from that of road system. Following this phenomenological feature of the subgrade system, this paper introduces the implementation of the resilient modulus based constitutive model on a commercial finite element software. The implementation of the resilient modulus models such as K-${\theta}$ and Uzan on a FE program has been conducted previously. These model assumes that the material state reaches to the nonlinear elastic condition and with further application of repetitive loads, the response of material is completed in elastic condition. According to the recent test results performed on cohesive subgrade soils, however, permanent deformation occurs with repetitive loads. With aids of previously suggested models the permanent deformation cannot be modeled. To overcome such limitation a plastic potential derived from the test results and simple failure criterion based constitutive model is developed. The comparison between the analysis and test results shows a good correlation.

• Journal of the Korean GEO-environmental Society
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• v.12 no.12
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• pp.63-70
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• 2011

Expanded Polystyrene (EPS) is a type of geosynthetic material manufactured with various strengths, unit weights, and dimensions. Due to recent advances in research on EPS, the use of EPS has increased dramatically. This super light weight material has a unit weight of approximately $0.16{\sim}0.47kN/m^3$, equivalent to 6.3~15.7 of that of most natural soils with conditions of fill materials. In spite of this advantage, it is noted that no standard method of resilient modulus test on EPS geofoam was reported and no literature on resilient modulus test methods for EPS geofoam exist. The main object of this study was to investigate feasibility of the resilient modulus of EPS when it was applied for flexible pavement. The investigation of the feasibility was completed based on the results from triaxial tests.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.10a
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• pp.113-118
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• 2004

Experiments are conducted to get basic information of under-expanded impinging jet in the near field. Experimental parameters are impinging angle and under-expanded ratio. As the under-expanded ratio increases, the maximum surface pressure decreases and the reducing effect of recovery factor increases. As the impinging angle decreases, the peak of surface pressure is displaced slightly from the geometric center of the plate to the upward region and the cooling region is expanded in the downward region, whereas it is contracted in the upward region.