• Magazine of the Korean Society of Agricultural Engineers
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• v.33 no.2
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• pp.82-93
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• 1991

The objective of this paper is to show that the soil-geotextile interaction needs to he addressed in addition to the usual tensile and modulus properties when the geotextile is being designed for a specific application. The soil-geotextile interaction can be directly assessed by standard direct shear test. The data presented here show that the shear strength paramaters describing the soil-geotextile interface can he greatly influenced by the type of the geotextile. In this investigation, we examined nine different geotextiles of varying construction and surface textures with two standard soil, under five loading conditions, and compared the shear strength and the frictional resistance with the corresponding values of soil itself The following conclusions were drawned from this study. 1. The shear stress-strain curve shows that there are the residual shear stresses at the soil-geotextile interface. Because of the hydraulic gradient between the soil and the geotextile, the excessive pore water can migrate into the geotextile and among the filaments and dissipate through the soil-geotextile interface. 2. The shear strength of the soil-geotextile interface is affected by the moisture content of the soil. At moisture content lower than the optimum water content of the Proctor compaction test, the shear strength of the soil-geotextile interface is greater. 3. The type and surface roughness of the geotextile have the greatest influence on the interface friction angle between the soil and the geotextile.

• Journal of the Korean Society of Safety
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• v.22 no.4
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• pp.57-65
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• 2007

Effects on the stiffness of the embankment and sandmat on the construction safety of road embankment was investigated in this study by the numerical experiments using FEM. Two points was mainly focused in this study especially. First the deformation characteristics by the change of the stiffness of sand mat and embankment was investigated by the analyzing the consolidation settlement at the center of the embankment and the lateral displacement at the toe of the embankment. And, the effect of the stiffness on the stress distribution characteristics was also investigated in this study. Furthermore, slope stability analysis was carried out to gain the safe factor by change the stiffness of the sandmat and the embankment. The objective of the study is supplying the result of the numerical experiments for the geotechnical engineers who use the FEM for the safety design of the soil structures. As a result, the stiffness of the superstructures greatly affects on the deformation characteristics both in consolidation settlement and lateral displacement. However, it can be aware that it is not dominants to the stress distribution in the aspect that the no changes in the residual excess pore water pressure. Therefore, the decision of the stiffness has to be carried out deliberately considering not only the consolidation the magnitude of the settlement and the lateral displacement, but the slope stability.

• Journal of the Korean Geosynthetics Society
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• v.16 no.1
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• pp.73-83
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• 2017

Laboratory and in-situ tests were conducted to evaluate the cone factors for the layers with low plasticity containing a lot of silty and sand soils from the west coast (Incheon, Hwaseong and Gunsan areas) and its applicability was evaluated based on these results. The cone factors were evaluated from 19 to 23 based on unconfined compression strengths (qu), from 13 to 13.8 based on simple CU strengths and from 11.6 to 13.1 based on field vane strengths, respectively. The unconfined compression strengths of undisturbed silty soil samples with low plasticity were considerably underestimated due to the change of in-situ residual effective stress during sampling. Half of unconfined compression strength (qu/2) based cone factors of silty soils with low plasticity fluctuated and were approximately 1.8 times higher than simple CU based values of these soils. When evaluating cone factors of these soils, it should be judged overall on the physical properties such as the grain size distribution and soil plasticity and on the fluctuation of the corrected cone resistance and the sleeve friction due to the distribution of sandseam in the ground including pore pressure parameter.

• Journal of the Korean GEO-environmental Society
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• v.15 no.3
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• pp.5-13
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• 2014

This paper presents the results of a numerical investigation on applicability of Light-weighted Foam Soils (LWFS) consisted of dredged soils for soft ground improvement. The engineering properties of LWFS were comprehensively investigated based on the previous experimental tests. And three dimensional numerical models which reflect soft ground conditions were adopted to evaluate the applicability of LWFS compared to SCP and DCM. A number of cases were analyzed using a stress-pore pressure coupled model. The results indicated that LWFS method enables to reduce more settlement, lateral flow and heaving than SCP method and enable to reduce more residual settlement than DCM method. Also it was revealed that such effect depends on the properties of LWFS such as unit weight, unconfined compressive strength, deformation modulus and Poisson's ratio.

• Tribology and Lubricants
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• v.31 no.2
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• pp.56-61
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• 2015

In this study, we investigated the effectiveness of an ultrasonic nanocrystal surface modification (UNSM) technique on the mechanical and wear properties of tungsten carbide (WC). The UNSM technique is a newly developed surface modification technique that increases the mechanical properties of materials by severe plastic deformation. The objective of this study was to improve the wear resistance of press die made of WC by applying the UNSM technique. We observed the microstructures of the untreated and UNSM-treated specimens using a scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDX) was used to investigate the chemical composition. The SEM observations showed the pore size and the number of pores decreased after the UNSM treatment. We assessed the wear behavior of both the untreated and UNSM-treated specimens using a scratch test. The test results showed that the wear resistance of the UNSM-treated specimens increased by about 46% compared with the untreated specimens. This may be attributed to increased hardness, reduced surface roughness, induced compressive residual stress, and refined grain size following the application of the UNSM technique. In addition, we found that the UNSM treatment increased the carbon concentration to 63% from 33%. We expect that implementing the findings of this study will lead to an increase in the life of press dies.

• Tribology and Lubricants
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• v.34 no.6
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• pp.270-278
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• 2018

STS 316L prepared by additive manufacturing (AM) exhibits deterioration of mechanical properties and wear resistance due to the presence of defects such as black-of-fusion defects, internal porosity, residual stress, and anisotropy. In addition, high surface roughness (integrity) of AM products remains an issue. This study aimed to apply ultrasonic nanocrystal surface modification (UNSM) technology to STS 316L prepared by AM to increase the surface hardness, to reduce the surface roughness, and to improve the friction and wear behavior to the level achieved by bulk material manufactured using traditional processes. Herein, the as-received and polished specimens were treated by UNSM technology and their resulting properties were compared and discussed. The results showed that UNSM technology increased the surface hardness and reduced the surface roughness of the as-received and polished specimens. These results can be attributed to grain size refinement and pore elimination from the surface. Moreover, the friction of the as-received and polished specimens after UNSM technology was lower compared to those of the as-received and polished specimens, but no significant differences in wear resistance were found.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.1
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• pp.20-27
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• 2013

Seabed settlement underneath a coastal structure may occur due to wave loading generated by storm surge. If the foundation seabed consists of sandy soil, the possibility of the seabed settlement may be more susceptible because of generation of residual excess pore-water pressure and cyclic mobility. However, most coastal structures, such as breakwater, quay wall, etc., are designed by considering wave load assumed to be static condition as an uniform load and the wave load only acts on the structure. In real conditions, however, the wave load is dynamically applied to seabed as well as the coastal structure. In this study, therefore, a real-time wave load is considered and which is assumed acting on both the structure and seabed. Based on a numerical analysis, it was found that there exists a significant effect of wave load on the structure and seabed. The deformation behavior of the seabed according to time was simulated, and other related factors such as the variation of effective stress and the change of effective stress path in the seabed were clearly observed.

• Journal of the Korean Geotechnical Society
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• v.32 no.6
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• pp.49-59
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• 2016

We develop liquefaction resistance curves, which represent the correlation between cyclic resistance ratio (CRR) and number of cycles (N) to estimate the build-up of residual excess pore pressure from simple shear tests performed for this study and also from published literature. The liquefaction curve is calculated from two models. The comparisons show that one of the models is not reliable because it underestimates CRR. The scatter of the data is shown to be significantly reduced when CRR is normalized to the resistance ratio at N = 15 ($CRR_{N=15}$). Use of the normalization is particularly useful because CRR can be easily estimated from field tests. From normalization, we propose mean, upper, and lower curves. The corresponding design equation and its parameters are also proposed. We believe that the proposed curves can be used for effective stress site response analyses and evaluation of the seismic performance of port structures.

• Economic and Environmental Geology
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• v.46 no.1
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• pp.51-61
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• 2013

Researches on the oil recovery enhancement using the nanotechnology has recently been studied in the United States. The previous researches has focused mainly on the flow characteristics of nanoparticles in porous media, and the stability of the nano-emulsion itself. However, the analysis did not deal with the size effects between a nano-emulsion and the pore size which has an important role when nano-emulsion flows in the porous media. In this research, nano-based emulsion was fabricated which is able to be applied for the enhanced oil recovery techniques and its characteristics was analyzed. In addition, in order to identify the characteristics of nano-emulsions flowing through the porous media, the size effect was analysed by filtering test. According to the results, when the emulsion was fabricated, SCA(Silane Coupling Agent) or PVA(Poly Vinyl Alcohol) are added to improve the stability of emulsion. As the ratio of the decane to water increased, the viscosity of emulsion and the droplet size also increased. For the filtering test at the atmospheric conditions, the droplet did not go through the filter; only the separated water from the emulsion was able to be filtered. This phenomenon occurred because the droplet was not able to overcome the capillary pressure. At the filtering test by suction pressure, most of the emulsion was filtered over the filter size of $60{\mu}m$. However, the ratio of filtration was rapidly degraded at less than $45{\mu}m$ filters. This is caused due to deformation and destruction of the droplet by strong shear stress when passing through the pore. The results from the study on the basic characteristic of nano-emulsion and filtering test will be expected to play as the important role for the fabrication of the stable nano-emulsion or the research on the recovery of residual oil in porous media.