• Membrane Journal
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• v.31 no.1
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• pp.16-34
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• 2021

Water supplies are decreasing in comparison to increasing clean water demands. Using nanofiltration is one of the most effective and economical methods to meet the need for clean water. Common methods for desalination are reverse osmosis and nanofiltration. However, pristine membranes lack the essential features which are, stability, economic efficiency, antibacterial and antifouling performances. To enhance the properties of the pristine membranes, graphene oxide (GO) is a promising and widely researched material for thin film composites (TFC) membrane due to their characteristics that help improve the hydrophilicity and anti-fouling properties. Modification of the membrane can be done on different layers. The thin film composite membranes are composed of three different layers, the top filtering active thin polyamide (PA) layer, supporting porous layer, and supporting fabric. Forward osmosis (FO) process is yet another energy efficient desalination process, but its efficiency is affected due to biofouling. Incorporation of GO enhance antibacterial properties leading to reduction of biofilm formation on the membrane surface. Pressure retarded osmosis (PRO) is an excellent process to generate clean energy from sea water and the biofouling of membrane is reduced by introduction of GO into the active layer of the TFC membrane. Different modifications on the membranes are being researched, each modification with its own advantages and disadvantages. In this review, modifications of nanofiltration membranes and their composites, characterization, and performances are discussed.

• Journal of the Korean GEO-environmental Society
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• v.10 no.2
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• pp.51-59
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• 2009

This study is based on field data obtained from rock grouting such as RQD value, Unit cement grout volume, Lugeon value(Lu), and Maximum grout pressure in four different dam sites. The relationship were analyzed and compared as follow. The cut-off effect after rock grouting in dam-foundation which are mostly consist of metamorphic rock is better than that of Sedimentary rock. And the impermeable effect after consolidation grouting is more efficiency than the impermeable effect after curtain grouting. The unit cement grout volume are increased as RQD value is higher in rock mass. But there is no relationship between RQD value and Lugeon value. In the sedimentary rock, which is more permeable than metamorphic rock, Lugeon value (Lu) is a linear function (Lu=0.22Vc) of unit cement grout volume (Vc). Cut-off effect of curtain grouting is less influential at each near holes which are already grouted than that of consolidation grouting. And the behavior characteristics of Lugeon value vs. the unit cement grout volume as the order of installations are almost the same.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1472-1477
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• 2009

The landfill ground that consists of sandy soil or contains boulder or has waste ground such as waste landfill can be often applied by dynamic compaction method considering quick construction and economic advantages. In this study, the improvement efficiency of the dynamic compaction method that is used on the waste disposal ground of Tague Freight Terminal constrution site is analyzed. The results show that the N values are increased from 6.5/30 to 22.5/30, which is 3.5 times increase compared with the N value before dynamic compaction. The amount of settlement is in the range of 0.706~1.729m. the $\alpha$ vlues suggested by Leonards et al.(1980) was about 0.25~0.48, which are quite similar to to not only 0.3~0.5 of the findings of waste layer of the Society of Soil Engineering of Japan (1987) but also 0.35~0.4 of that of mine waste of Lukas (1986).

• Journal of the Korean Geotechnical Society
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• v.34 no.11
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• pp.43-55
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• 2018

AGF (Artificial Ground Freezing) method is a temporary ground improvement method which can apply to all types of soil with the purpose of high stiffness and low hydraulic conductivity. However, the groundwater flow and the heterogeneity of the ground increase the uncertainty of the ice-column formation which hinders the reliability of this method. The effects of groundwater flow and layered heterogeneity on ice-wall integrity by AGF method were analyzed using finite element analysis program for a coupled thermo-hydro phenomena in the freezing ground. Groundwater flow changes circular ice-column into elliptical shapes and increases the time required for the formation of ice walls. The previous theoretical formula overestimated the completion time of the ice wall and the critical groundwater velocity by neglecting the thermal interaction between adjacent ice-columns. Numerical results presented the corrected formula and verified the proposed equation for the dimensionless ice-wall completion time. In the layered heterogeneous ground, the thickness of the layer with higher hydraulic conductivity and its relative magnitude were found to be important factors in the ice-wall completion time and critical velocity.

• Journal of Wetlands Research
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• v.22 no.1
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• pp.31-38
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• 2020

Weirs are to secure amount water of streams and drop structures are to enhance stabilization of stream bed and bridges are to connect isolated region, which are called stream crossing structures. In the stream design criteria, directions for minimum size of structures are suggested to secure stability of stream crossing structures. However the sizes of almost all existing weirs and drop structures are not satisfied with the stream design criteria and only 22 percent of the peirs of bridges are satisfied. To enhance hydraulic stability of existing weirs and drop structures, it is required that the ratio of bed protection to apron should be above 3.3. According to factual survey of structures in the sample streams, it has been shown that the longitudinal slope of rapid works with 1:20 is the most reasonable to design velocity if existing weirs and drop structures are rehabilitated into rapid works. It has been known that violating freeboard and span length of piers should make existing bridges reconstructed or removed. However, comprehensive review including deterioration level of bridges, special regulation for span length, etc. should be considered to determine rehabilitation plan of bridges. In this study, a procedure has been suggested to improve hydraulic stability of weirs, drop structures and piers of bridges. Sound environment of stream and reduction of natural disaster could be achieved by improving stability of cross structures, which could be obtained by governmental budget and active stream management including observance of design criteria.

• Journal of the Korean GEO-environmental Society
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• v.16 no.8
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• pp.5-12
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• 2015

In this study, buoyancy-resistance permanent anchor was considered to prevent uplift pressure of a building structure. However, this test was failed to put anchor body in the boring hole because of the rapid outflow of ground water and coefficient of permeability. In addition, the hole where the anchor body was forcefully inserted constantly flew the sea water and cement. And it was found that anchor was not settled in the ground. In order to solve this problem, jet grouting method was applied to block the ground water and the single grouted column method was chosen to install the buoyancy-resistance permanent anchor. In this paper, the single grouted column method was applied with the general jet grouting methods and grout material was fixed by 3-field tests. These tests confirmed the effect of permeability and ground improvement with field permeability test by core sampling, Standard Penetration Test (SPT) and unconfined compression test. Confirming the stability of the buoyancy-resistance permanent anchor with installation and tension test, application of the single grouted column method in the volcanic clastic zones was verified.

• Geotechnical Engineering
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• v.13 no.6
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• pp.5-12
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• 1997

Predictions of settlements under preloading for the improvement of soft soil is a very important element of construction management. Due to the non uniformity, difficulty of estimating resonable soil properties, predictions of settlements and settlement velocities at the design stage seldom agree with the actual future settlements. To overcome this problem, the prediction methods based on the settlement observation of initial preloading stage such as hyperbolic method and Asaoka method have been employed frequently. However the estimating method for the reliability of these predictions at the time of prediction has not been suggested. In this study, comparisons of predicted settlements by hyperbolic met hed and observed settlements are explored through case studies. And a stratagem of estimating reliability of settlement predictions by hyperbolic method is suggested as the result of investigation on the relationship between the initial observed time and error of settlement prediction by hyperbolic method.

• Journal of the Korean Geotechnical Society
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• v.21 no.3
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• pp.79-85
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• 2005

An experimental study was carried out to investigate the recycling possibility of waste oyster shells, which induce environmental pollutions by piling up out at the open or the temporary reclamation. The purpose of this study is to develope eco-friendly binder using waste oyster shells, and to reinforce dredged soils fur soft soil improvement. In this paper, a series of laboratory tests including compressive strength tests were performed to evaluate strength characteristics of soils treated by developed binder with different water content of dredged soils, mixing rates of binder, curing days. Based on test results, eco-friendly binders manufactured from waste oyster shells were estimated as good resource materials for soft soil improvements.

• Journal of the Korean Geotechnical Society
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• v.21 no.1
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• pp.105-114
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• 2005

An in-hole seismic method, which has been developed for measuring dynamic properties of subsurface materials, was improved in terms of cost effectiveness and practicality. The upgraded features include the motorized triggering system rather than the manual prototype version in the previous studies and a connecting rod between source and receiver in the module. The probe, thus, can be used for the field measurements of soil properties as well as those of rocks. The performance of the probe has been evaluated through extensive cross-hole tests and in-hole tests at various sites.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.159-165
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• 2002

Soil cement which is a mixture of soil, cement, and water has a broad range of applications since it is economical, ecological, and easy to use, repair, and reinforce. Its applications include pavements, stabilization of slopes, retaining walls, and improvements of soft ground to name a few. Other types of chemicals are often added to increase its strength. This study investigated unconfined compressive strength of cured soil cement mixed with New Soil Chemical(NSC). The investigation involved laboratory experiments under various conditions including soil type, cement content, and ratios of water to NSC. Results of the study show that NSC enhanced the unconfined compressive strength significantly, and the degree of enhancement was varied with test conditions.