• Journal of Ocean Engineering and Technology
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• v.12 no.3 s.29
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• pp.19-30
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• 1998

In this paper, the dynamic analysis of a dolphin system for mooring a floating structure such as barge mounted plant is studied. The characteristics of the soil-pile system are simplified by a set of equivalent spring elements at the mudline. To evaluate the equivalent spring constants, the finite difference method is used. Since the characteristics of the soil-pile system are nonlinear in case of soft foundation, the nonlinear dynamic analysis technique is needed. The Newmark $beta$ method incorporating the modified Newton-Raphson method(initial stiffness method) is used. A numerical analysis is performed on two mooring dolphin systems on soft foundation and rock foundation. In case of the rock foundation, the characteristics are found to be nearly linear, so the linear dynamic analysis may be sufficient to consider the foundation effect. But in case of soft foundation, the non-linearity of the foundation appears to be very signigicant, so the nonlinear dynamic analysis si needed.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.1
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• pp.33-40
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• 2009

Compacted soil are used in almost roadway construction with compaction of soil. The direct consequence of soil compaction is densification, which in turn results in higher strength, lower compressibility, and lower permeability. The standard and modified Proctor tests are the most common methods. Both of these tests utilize impact compaction, although impact compaction shows no resemblance to any type of field compaction and is ineffective for granular soils. It has been dramatic advances in field compaction equipment. Therefore, the Proctor tests no longer represent the maximum achievable field density. The main objectives of this research are a survey of current field compaction equipment, laboratory investigation of compaction characteristics, and field study of compaction characteristics. The findings from the laboratory and compaction program were used to establish preliminary guidelines for suitable laboratory compaction procedures.

• Structural Engineering and Mechanics
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• v.24 no.1
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• pp.51-62
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• 2006

Differential transform method (DTM) for free vibration analysis of both ends simply supported beam resting on elastic foundation is suggested. The fourth order partial differential equation for free vibration of the beam resting on elastic foundation subjected to bending moment, shear and axial compressive load is obtained by using Winkler hypothesis and small displacement theory. It is assumed that the material is linear-elastic, and that axial load and modulus of subgrade reaction to be constant. In the analysis, shear and axial load effects are considered. The frequency factors of the beam are calculated by using DTM due to the values of relative stiffness; the results are presented in graphs and tables.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1992.04a
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• pp.7-12
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• 1992

The variable node plate bending element, ie, the element with one or two additional mid-side nodes is used in the analysis of mat foundation to generate the nearly ideal grid model in which more nodes are defined near the column location. The plate bending element used in this study is the one based on Mindlin/Reissner plate theory with substitute shear strain field and the nodal stresses of that element are obtained by the local smoothing technique. The interaction of the soil material with the mat foundation is modeled with Winkler springs connected to the nodal points in the mat model. The vertical stiffness of the soil material are represented in terms of a modulus of subgrade reaction and are computed in the same way as to the computation of consistent nodal force of uniform surface loading. Several mesh schemes were proposed and tested to find the most suitable scheme for mat foundation analysis.

• Proceedings of the KSR Conference
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• 2001.10a
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• pp.562-567
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• 2001

In this study, performance of reinforced railroad roadbeds with the slag(HMS-25) and soil were investigated through the real scale railroad roadbed tests. Several real scale reinforced railroad roadbeds were constructed in the laboratory with different subgrade conditions and were tested with the estimated actual train loads including the impact loading of train. The affecting factors such as plastic ＆ elastic settlement roadbed layers as well as surface of rails were measured. The settlement at rail surface and roadbed surface of case of soil and slag roadbed comparative with good roadbed site were 2.3, 5.7 times and 1.9, 1.6 times, respectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.911-916
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• 2002

One of important roles of concrete track is to reduce vibration transmitting to subgrade. In this paper, a numerical method for evaluating the effects of vibration reduction of concrete track is presented. Using the method, high frequency dynamic analyses and track-tunnel-soil interaction analyses are carried out for three types of concrete track in order to investigate the vibration reduction effects compared with normal ballast track.

• Journal of the Korean Society for Railway
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• v.5 no.2
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• pp.70-76
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• 2002

In this study, performance of reinforced railroad roadbeds with the reinforced roadbed materials were investigated through the real scale roadbed tests. It was also found that the reinforced roadbed with reinforced roadbed materials has less elastic and plastic settlement than the one with soil. The slag roadbed was more effective than the crushed stone roadbed with the same condition for load distribution. Therefore considering overall characteristics of reinforced roadbed material, the optimum thickness was recommended as 50 cm. Furthermore the real scale model test under the simulated rainfall condition, the settlement in the slag roadbed was about 8 times smaller than the settlement in the soil roadbed.

• Journal of the Korean GEO-environmental Society
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• v.20 no.2
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• pp.41-48
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• 2019

Soil compaction is one of the most important activities in the area of civil works, including road construction, airport construction, port construction and backfilling construction of structures. Soil compaction, particularly in road construction, can be categorized into subgrade compaction and roadbed compaction, and is significant work that when done poorly can serve as a factor causing poor construction due to a lack of compaction. Currently, there are many different types of compaction tests, and the plate bearing test and the unit weight of soil test based on the sand cone method are commonly used to measure the degree of compaction, but many other methods are under development as it is difficult to secure economic efficiency. For the purpose of this research, a portable penetration meter called the Free-Fall Penetration Test (FFPT) was developed and manufactured. In this study, a homogeneous sample was obtained from the construction site and soil was classified through a sieve analysis test in order to perform grain size analysis and a specific gravity test for an indoor test. The principle of FFPT is that the penetration needle installed at the tip of an object put into free fall using gravity is used to measure the depth of penetration into the road surface after subgrade or roadbed compaction has been completed; the degree of compaction is obtained through the unit weight of soil test according to the sand cone method and the relationship between the degree of compaction and the depth of the penetration needle is verified. The maximum allowable grain size of soil is 2.36 mm. For $A_1$ compaction, a trend line was developed using the result of the test performed from a drop height of 10 cm, and coefficient of determination of the trend line was $R^2=0.8677$, while for $D_2$ compaction, coefficient of determination of the trend line was $R^2=0.9815$ when testing at a drop height of 20 cm. Free fall test was carried out with the drop height adjusted from 10 cm to 50 cm at increments of 10 cm. This study intends to compare and analyze the correlation between the degree of compaction obtained from the unit weight of soil test based on the sand cone method and the depth of penetration of the penetration needle obtained from the FFPT meter. As such, it is expected that a portable penetration tester will make it easy to test the degree of compaction at many construction sites, and will lead to a reduction in time, equipment, and manpower which are the disadvantages of the current degree of compaction test, ultimately contributing to accurate and simple measurements of the degree of compaction as well as greater economic feasibility.

• Geomechanics and Engineering
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• v.22 no.3
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• pp.227-236
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• 2020

Expansive soils are renowned for their swelling-shrinkage property and these volumetric changes resultantly cause huge damage to civil infrastructures. Likewise, subgrades consisting of expansive soils instigate serviceability failures in pavements across various regions of Pakistan and worldwide. This study presents the use of polypropylene fibers to improve the engineering properties of a local swelling soil. The moisture-density relationship, unconfined compressive strength (UCS) and elastic modulus (E₅₀), California bearing ratio (CBR) and one-dimensional consolidation behavior of the soil treated with 0, 0.2, 0.4, 0.6 and 0.8% fibers have been investigated in this study. It is found that the maximum dry density of reinforced soil slightly decreased by 2.8% due to replacement of heavier soil particles by light-weight fibers and the optimum moisture content remained almost unaffected due to non-absorbent nature of the fibers. A significant improvement has been observed in UCS (an increase of 279%), E₅₀ (an increase of 113.6%) and CBR value (an increase of 94.4% under unsoaked and an increase of 55.6% under soaked conditions) of the soil reinforced with 0.4% fibers, thereby providing a better quality subgrade for the construction of pavements on such soils. Free swell and swell pressure of the soil also significantly reduced (94.4% and 87.9%, respectively) with the addition of 0.8% fibers and eventually converting the medium swelling soil to a low swelling class. Similarly, the compression and rebound indices also reduced by 69.9% and 88%, respectively with fiber inclusion of 0.8%. From the experimental evaluations, it emerges that polypropylene fiber has great potential as a low cost and sustainable stabilizing material for widespread swelling soils.

• Journal of the Korean Society for Railway
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• v.16 no.5
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• pp.386-393
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• 2013

In this study, the so-called repeated plate load bearing test (RPBT) used to get $E_{v2}$ values in order to check the degree of compaction of subgrade, and to get design parameters for determining the thickness of the trackbed foundation, is investigated. The test procedure of the RPBT method is scrutinized in detail. $E_{v2}$ values obtained from the field were verified in order to check the reliability of the test data. The $E_{v2}$ values obtained from high-speed rail construction sites were compared to converted modulus values obtained from resonant column (RC) test results. For these tests, medium-size samples composed of the same soils from the field were used after analyzing stress and strain levels existing in the soil below the repeated loading plates. Finite element analyses, using the PLAXIS and ABAQUS programs, were performed in order to investigate the impact of the strain influence coefficient. This was done by getting newly computed $I_z$ to get the precise strain level predicted on the subgrade surface in the full track structure; under wheel loading. It was verified that it is necessary to use precise loading steps to construct nonlinear load-settlement curves from RPBT in order to get correct $E_{v2}$ values at the proper strain levels.