• International Journal of Highway Engineering
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• 제6권3호
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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.

• International Journal of Highway Engineering
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• 제12권4호
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• pp.147-155
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• 2010

A prediction model of resilient modulus($E_R$) was developed for recycled crushed-rock-soil mixtures. The evaluation of $E_R$, using the "orthodox" repeated loading tri-axial test, is not feasible for such a large-size gravelly material. An alternative method was proposed hereby using the subtle different modulus called nonlinear dynamic modulus. The prediction model was developed by utilizing in-situ measured shear modulus($G_{max}$) and its reduction curves of modeled materials using the large free-free resonant column test. A pilot evaluation of the model parameters was carried out for recycled crushed-rock-soil-mixture at a highway construction site near Gimcheon, Korea. The values of the model parameters($A_E,\;n_E,\;{\varepsilon}_r\;and\;{\alpha}$) were proposed as 9618, 0.47, 0.0135, and 0.8, respectively.

• International Journal of Highway Engineering
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• 제10권4호
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• pp.31-40
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• 2008

The dynamic moduli of asphalt concrete are very important for the analysis and the design of asphalt pavement systems. The dynamic modulus master curve is usually represented by a sigmoidal function. The Ramberg-Osgood model was widely used for fitting of normalized modulus reduction curves with strain of soils in soil dynamic fields. The master curves were obtained by both sigmoidal functions and modified Ramberg-Osgood model for the same dynamic modulus data set, the fitting abilities of both methods were excellent. The coefficients in sigmoidal function are coupled. Therefore, it is not possible to separate the characteristics of the master curve with absolute value and shape. However, the each fitting coefficient in the Ramberg-Osgood model has a unique effect on the master curve, and the coefficients are not coupled with each other.

• Journal of the Korean Geotechnical Society
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• 제22권12호
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• pp.15-24
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• 2006

The evaluation of shear modulus is very important in various fields of civil engineering. Non-destructive seismic methods can be used to determine shear wave velocity ($V_s$) profile. Non-destructive seismic methods geneally consist of three steps: field testing, evaluation of dispersion curve, and determination of Vs profile by inversion process. Non-destructive seismic methods can be divided into two categories according to the number of receivers used for data reduction: two-channel tests and multi-channel tests. Two channel tests use apparent velocity dispersion curve and multi-channel tests use mode dispersion curves. Multi-channel tests using mode dispersion curve can reduce calculation time to determine soil profile and uncertainties in inversion process. So far, only multi-channel tests can determine mode dispersion curves but multi-channel test needs many receivers to determine reasonable mode dispersion curves. In this paper, HWAW (Harmonic Wavelet Analysis of Wave) method is applied to determine mode dispersion curves. HWAW method uses short test setup which consists of two receivers with a spacing of 1 to 3 m. Through numerical simulations and field application, it is shown that HWAW can determine resonable mode disperson curves.

• Proceedings of the Korean Geotechical Society Conference
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• 한국지반공학회 2004년도 춘계학술발표회
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• pp.968-976
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• 2004

In the paper, deformation characteristics of fiber-mixed-soils, mixed polypropylene staple fibers of 0.3% fiber content with sands of various gradation, and their effectiveness of reinforcement were evaluated. A series of Resonant Column tests were performed with specimens prepared with varying Uniformity Coefficient and constant Curvature Coefficient. Maximum shear moduli 01 fiber-mixed-soils were increased by up to 30% and modulus reduction was also restrained in nonlinear range. Normalized shear modulus reduction curves of fiber-mixed-soils shift close to the upper limit of Seed curd Idriss's curves and are located within narrower band than those of unmixed soils, which proves the effectiveness on stiffness increment by reinforcing soils with fibers.

• Journal of the Korean Geotechnical Society
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• 제25권12호
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• pp.87-105
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• 2009

Nonlinear dynamic deformation characteristics, expressed in terms of normalized shear modulus reduction curve (G/$G_{max}-\log\gamma$, G/$G_{max}$ curve) and damping curve (D-$\log\gamma$), are important input parameters with shear wave velocity profile ($V_s$-profile) in the seismic analysis of (new or existing) fill dam. In this paper, the reasonable and economical methods to evaluate the nonlinear dynamic deformation characteristics for core zone and rockfill zone respectively are presented. For the core zone, 111 G/$G_{max}$ curves and 98 damping curves which meet the requirements of core material were compiled and representative curves and ranges were proposed for the three ranges of confining pressure (0~100 kPa, 100 kPa~200 kPa, more than 200 kPa). The reliability of the proposed curves for the core zone were verified by comparing with the resonant column test results of two kinds of core materials. For the rockfill zone, 135 G/$G_{max}$ curves and 65 damping curves were compiled from the test results of gravelly materials using large scale testing equipments. The representative curves and ranges for G/$G_{max}$ were proposed for the three ranges of confining pressure (0~50 kPa, 50 kPa~100 kPa, more than 100 kPa) and those for damping were proposed independently of confining pressure. The reliability of the proposed curves for the rockfill zone were verified by comparing with the large scale triaxial test results of rockfill materials in the B-dam which is being constructed.

• International Journal of Highway Engineering
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• 제9권4호
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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.

• Journal of the Earthquake Engineering Society of Korea
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• 제8권3호
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• pp.33-42
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• 2004

While transforming the inelastic system into the equivalent elastic one gives an advantage of simpler analysis, the actual inelastic behavior of the system is hardly modeled in the capacity spectrum method (CSM). Therefore, the accuracy of CSM depends on the precise estimation of equivalent period and damping ratio as well as the modification of the elastic response spectrum and the corresponding demand spectrum. In this paper, the effect of demand spectrums on the accuracy of CSM is evaluated. First, the response reduction factors provided in ATC-40 and Euro Code are evaluated. Numerical analysis results indicated that the acceleration responses obtained using the factor of Euro Code are closer to the actual response than those obtained using the factors of ATC-40. Next, the accuracy of CSM is evaluated constructing the demand spectrum using the absolute acceleration responses and pseudo acceleration responses. The results obtained using the absolute acceleration responses were found to be generally larger than those obtained using the pseudo ones. Since CSM often underestimates the response, the use of absolute acceleration response gives the response relatively closer to the exact ones. However, the difference becomes negligible as the hardening ratio and the yield strength ratio become larger.

• Journal of the Korean Recycled Construction Resources Institute
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• 제6권4호
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• pp.311-318
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• 2018

When reinforced concrete structures are exposed to fire, their mechanical properties such as compressive strength, elasticity coefficient and rebar yield strength, are degraded. Therefore, the structure's damage assessment is essential in determining whether to dismantle or augment the structure after a fire. In this study, the confinement effect of lateral reinforcement of RC column according to the numbers of fire exposure face and stirrup was verified by fire resistant test with the heating temperatures of $400^{\circ}C$, $600^{\circ}C$ and $800^{\circ}C$. The test results showed that the peak stress decreases and peak strain increases as the temperature is getting higher, also transverse ties are helpful in improving the compressive resistance of concrete subjected to high temperature. Based on the results of this study, the residual stress of confined concrete under thermal damage is higher at the condition of more lateral reinforcement ratio and less fire exposure faces. The decreasing ratio of elastic modulus of more confined and less exposure faces from the relationship of load and displacement was also smaller than that of opposite conditions.

• Journal of the Korean Geotechnical Society
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• 제18권5호
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• pp.109-122
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• 2002

The water content of soil near the ground subgrade varies seasonally, and dynamic deformational characteristics of soil are affected by the variation of water content. Contrary to previous studies which used various specimens of different compaction moisture contents, the influences of water content and capillary Pressure on dynamic deformational characteristics of soil were investigated using the given specimen controlling the matric suction. RC/TS(resonant column and torsional shear) testing equipment was modified so that it can control water content with changing capillary pressure(matric suction). RC/TS tests were performed on subgrade soil collected in the KHC(Korea Highway Corporation) test road. In the field, the cross-hole tests were performed and the water contents were measured at the same site to verify the feasibility and applicability of RC/TS test results. As water content decreased, the tendency of increasing shear moduli in field was well matched with laboratory test results.