• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1404-1414
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• 2008

In the mechanistic-empirical trackbed design of railways, the resilient modulus is the key input parameter. This study focused on the resilient modulus prediction model, which is the functions of mean effective principal stress and axial strain, for three types of railroad trackbed materials such as crushed stone, weathered soil, and crushed-rock soil mixture. The model is composed with the maximum Young's modulus and nonlinear values for higher strain in parallel with dynamic shear modulus. The maximum values is modeled by model parameters, $A_E$ and the power of mean effective principal stress, $n_E$. The nonlinear portion is represented by modified hyperbolic model, with the model parameters of reference strain, ${\varepsilon}_r$ and curvature coefficient, a. To assess the performance of the prediction models proposed herein, the elastic response of a test trackbed near PyeongTaek, Korea was evaluated using a 3-D nonlinear elastic computer program (GEOTRACK) and compared with measured elastic vertical displacement during the passages of freight and passenger trains. The material types of sub-ballasts are crushed stone and weathered granite soil, respectively. The calculated vertical displacements within the sub-ballasts are within the order of 0.6mm, and agree well with measured values with the reasonable margin. The prediction models are thus concluded to work properly in the preliminary investigation.

• Textile Coloration and Finishing
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• v.27 no.3
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• pp.165-174
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• 2015

To develop automobile parts, the unsaturated polyester based matrix resin(PR)/reinforcement(randomly oriented chopped E-glass fiber, GF) composites were prepared using sheet molding compound(SMC) compression molding. The effects of GF length(0.5, 1.0 1.5 and 2.0inch)/content (15, 20, 25, 30wt%) and number of ply(3, 4 and 5) on the specific gravity and mechanical properties of PR/GF composites were investigated in this study. The optimum length of GF was found to be about 1.0inch for achieving improved mechanical properties(tensile strength and initial modulus). The tensile strength and initial modulus of composites increased with increasing GF content up to 30wt%, which is favorable content range for SMC. The specific gravity, tensile strength/initial modulus, compressive strength/modulus, flexural strength/modulus and shear strength increased with increasing the number of ply up to 5, which is the maximum number of ply range for SMC. The effectiveness of ply number increased in the flexural strength > shear strength > compressive strength > tensile strength.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.176-181
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• 2010

The evaluation of shear modulus (or shear wave velocity) profile of the site is very important in various fields of geotechnical engineering. In the field, there exist spatial variations of shear modulus that case uncertainty in the geotechnical analysis or design. So it is necessary to evaluate the spatial variation of shear wave velocities of the soil site. In this study, the HWAW method is applied to the determination of a 3-D Vs map of soil site. The HWAW method, which is based on harmonic wavelet transforms, has been developed to determine phase and group velocities of waves. The HWAW method uses only the signal portion of the maximum local signal/noise ratio to evaluate the phase velocity in order to minimize the effect of the noise. The field testing of this method is relatively simple and fast because only one experimental setup, which consists of one pair of receivers on the surface, is needed using a short receiver spacing setup (1~3m). These characteristics make it possible to determine detailed local Vs profile in the site with lateral Vs variation and to evaluate 3-D Vs map by performing a series of tests on the grid. To estimate the applicability of the proposed method, field tests were performed. Through field applications validity and applicability of the proposed method were verified.

• Journal of the Korean Geotechnical Society
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• v.24 no.10
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• pp.33-43
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• 2008

In this study, for the purpose of evaluating the shear wave velocity in core zone, cross-hole test, down-hole test, MASW (Multi-channel Analysis of Surface Wave), and seismic reflection survey were carried out on the crest of the existing 'Y' dam. The results of field tests were compared one another. Furthermore, the field test results were compared with the result by the Sawada's empirical recommendation method. The purpose of this study is to compare the results of four kinds of field tests for evaluation of shear wave velocity in core zone of existing dam, to verify applicability of the empirical method which was recommended by Sawada and Takahashi, and to recommend a reasonable method for evaluation of shear wave velocity which is needed to evaluate tile maximum shear modulus of core zone. From the results of four kinds of field tests such as cross-hole test, down-hole test, MASW, and seismic reflection survey, it was found that the shear wave velocity distributions were similar within 18 m in depth and the results obtained by MASW and seismic reflection survey were almost the same by 30 m in depth. For evaluation of shear wave velocity in core zone of the existing dam, in consideration that it is not easy to bore the hole ill the core zone of existing dam, surface surveys such as MASW and seismic reflection method are recommended as realistic methods. On condition that it is impossible to conduct the field test and it is preliminary investigation, it is recommended that Sawada's low bound empirical equation be used.

• International Journal of Highway Engineering
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• v.3 no.1 s.7
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• pp.151-163
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• 2001

Very few studies have been attempted to understand the stress-strain behavior of flexible pavements reinforced with geosynthetics in the middle of asphalt layer. In this study, the flexible asphalt layer was analyzed with finite element method to understand stress-strain behavior. The asphalt layer was reinforced with glass grid and geogrid. The reinforcement was applied in the asphalt layer to prevent its excessive deformation and shear failure. The location of installation and stiffness of the geosynthetics were varied to obtain optimum depth of reinforcement and proper modulus. The results indicate that geosynthetics are more effective for reducing maximum shear stress than those of vertical stress and vertical displacement. Maximum shear stress decreased 15$\sim$20%, and glass grid with high value of modulus was the most effective. Also, in order to prevent failure of asphalt layer, reinforcement should be installed in the 3cm$\sim$5cm depth.

• Journal of the Korean Geotechnical Society
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• v.38 no.10
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• pp.41-48
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• 2022

The mass density of the medium (ρ) used to calculate the maximum shear modulus (G_max) of the saturated ground based on the shear wave velocity is unclear. Therefore, to determine the mass density, a verification formula and five scenarios were established. Laboratory tests were conducted, and the obtained results were compared. The mass density of the medium was assumed to be saturated (ρ_sat), wet (ρ_t), dry (ρ_dry), and submerged conditions (ρ_sub), and the V_s ratios of saturated to dry condition were obtained from each case. Assuming the saturated density (ρ_sat), the V_s ratio was consistent with the value from the resonant column test (RCT) results, and the value from the bender element test results was consistent with the wet density assumption (ρ_t). Considering the frequency range of earthquakes, it is concluded that applying the saturated density (ρ_sat) is reasonable as in the RCT results.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.846-853
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• 2006

In this study, quantitative sensitivity analysis on rockfill material influencing the dam crest displacement of Concrete-Faced Rockfill Dam(CFRD) was carried out. The purpose of this study is to indicate the most important input parameter and to show the quantitative variation of displacement at the crest of CFR type dam with this input parameter. The rockfill material properties for parametric study were obtained from the results of large scale triaxial tests on 34 rockfill materials in the 22 different sites. From the statistical analysis on these data, some statistical characteristics of rockfill material properties such as property range, distribution characteristics, and correlation between the properties were investigated. based on these characteristics, 27 property combinations were constituted by Latin Hypercube sampling method. Dam crest displacements after construction, impounding, and earthquake loading were evaluated by static and dynamic numerical analysis on each combination. From the sensitivity analysis, it was found that the crest displacement of CFR type dam was absolutely affected by the shear modulus of rockfill material and the effect of friction angle of it was negligible. This relative difference of sensitivity was more outstanding in case of crest settlement than in case of crest horizontal displacement. Also, it was found that the settlement and horizontal displacement of dam crest logarithmically decreased as the shear modulus increased and the difference between the maximum value and the minimum vale amounted to about 9.5 times in case of settlement and about 10 times in case of horizontal displacement.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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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.

• Transactions of the Korean Society of Mechanical Engineers
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• v.7 no.2
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• pp.161-167
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• 1983

In this study the phenomenon of cutting stress which arises on cutting tools and work pieces in cutting process is investigated by rake angle of cutting tools and feed for this measurement, P$_{s}$-1 (high modulus, photolastic Inc.) was used as a cutting tool, P$_{s}$-3 (medium modulus, photolastic Inc.) was used as work piece and reduction apparatus was attached to the head stock, and orthogonal cutting was adapted as a cutting method and transparent glass was used to block the strain in the orientation of thickness. The followings are the results of this study. (1) Photoelastic experimental equipments have made it possible to make dynamic measurement and analyze stress distribution in cutting tool and work piece surface which has hitherto been conducted only in static measurement and analyzing method. (2) The maximum stress arising at tools and work pieces in cutting process is on the tool edge tip, and the maximum stress arising on the tip of cutting tools is equal to that on the contacting area of work pieces in values. (3) The distributions of maximum shear stress on certain parts of the cutting tools and work pieces are as follows; for cutting tools, .alpha.=12.deg., .alpha.=0.deg., .alpha.=-12.deg. in order, and for work pieces, .alpha.=-12.deg., .alpha.=0.deg., .alpha.=12.deg. in opposite order.der.

• Journal of the Korean Geotechnical Society
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• v.33 no.4
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• pp.35-46
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• 2017

Most of high carbon fly ashes (HCFA) are discarded in landfills with high costs due to low recycling rate. This study aims to explore the geotechnical behaviors of HCFA mixtures reinforced with fiber and sand. A series of compaction test, unconfined compressive strength test and modified 1D consolidation test with bender element were performed. Specimens were prepared at their optimal moisture contents based on the results of compaction tests. The results of this study demonstrate that the inclusion of fibers to the matrix of HCFA increases unconfined compressive strength (UCS), strain at UCS, and maximum shear modulus ($G_{max}$) at a given void ratio. Reinforcement with sand increases UCS of HCFA; while the strain at UCS is irrelevant with sand fractions. Sand particles may disrupt the direct contacts between HCFA particles at low sand content, resulting in a decrease in $G_{max}$. However, it can be expected that the mixtures with sand content larger than 20% are in dense state; thus, $G_{max}$ of HCFA reinforced with sand shows greater value than that of unreinforced HCFA compacted with the same energy. Regardless of types of reinforcement, the compression index ($C_c$) of both fiber and sand reinforced HCFA is mainly determined by initial void ratio.