• Korean Journal of Environmental Biology
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• v.35 no.4
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• pp.604-621
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• 2017

This research was conducted to find the indigenous diatom species unrecorded in Korea from February to December 2016. The samples were taken at 28 sites of the coastal regions on the west coast of Korea and Jeju Island. Diatoms were collected mostly from sand and mud of tidal flats, including gravel, seaweed on the bottom and macrophytes floating in the seawater. Diatom specimens were observed by means of light and scanning electron microscopy. Twenty one species were discovered and added as new specimens to the Korean diatom flora, which are divided into 9 orders, 12 families, and 16 genera. The list and photographs of the species are included with the description of the morphological characteristics and distribution in Korea.

• Journal of Environmental Science International
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• v.22 no.2
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• pp.187-193
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• 2013

Dry matter allocation characteristics of Calystegia soldanella, grown in pots, was analysed to assess its plasticity in response to water-stressed conditions. As water was withheld leaf water potential between the two watering treatments was similar during the first 6 days, followed by a rapid decrease in water-stressed plants. The minimum leaf water potential was -1.50 MPa on day 15 and the maximum leaf water potential was about -0.5 MPa on day 0 in water-stressed plants. In well-watered plants leaf water potential was maintained almost consistently throughout the experiment. There was no significant difference in plant dry weight between the two watering treatments for 9 days after the start of experiment and that was remarkably increased thereafter, compared with that remained without any increase in water-stressed plants. In dry mass partitioning, however, the water-stressed plants showed a great plasticity, showing that there were 1.81, 1.35 and 0.81 times increase in root, stem and leaf, respectively. Dry mass partitioning in well-watered plants varied from 2% to 5%. The difference of dry mass partitioning between the two watering treatments was reflected in leaf mass per unit area (LMA) and root/shoot (R/S) ratio. LMA in water-stressed plants was lower than that in well-watered plants, while R/S ratio in water-stressed plants was higher in well-watered plants. This means that the water-stressed plants reduced its leaf area and increased dry mass partitioning into root and stem during the progress of soil drying. These results indicate that Calystegia soldanella inhabiting in sand dune cope with water stress with high plasticity which can adjust its dry mass partitioning according to soil water conditions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.1
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• pp.33-40
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• 1988

The new technique has been used to determine the soil-reinforcement interaction. The testing apparatus is essentially a triaxial cell fitted with the capability to house a hollow cylinderical sample. A hollow cylinderical sand specimen with a concentrical layer of reinfarcing material sandwitched in the middle is used in this investigation. The reinforcement is fastened at the base. The hollow specimen can be viewed as a "unit sheet" of a soil-reinforcement composite system of infinite horizontal extent. Axial load as well as inner and outer chamber pressures can be applied to perform a test. The specimen is first subjected to an isotropic stress state corresponding to the overburden pressure. Next, an extension test by reducing the axial load is carried out. The specimen is "loaded" to failure by either the breakage of reinforcing material (tensile failure) or slippage which takes place at the soil-reinforcement interface (i.e. the overcoming of the bonding capacity). Since the reinforcement is fastened at its lower end to the base, any tendency of relative movement between the reinforcement and the sand during an extension test can induce tensile force in the reinforcement thus forming a "reversed pull-out" test condition. Preliminary test results have demonstrated positively of the new approach to test the soil-reinforcement interaction. Reinforcing elements of different extensibility were used to study the deformbility of reinforced soil. Furthermore, both the breakage and the pull-out modes of failure were observed.

• Resources Recycling
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• v.12 no.5
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• pp.16-22
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• 2003

Lightweight aggregate for concrete was manufactured from recycling the waste PET bottles (PET Bottle Lightweight Aggregate, LAPET). The qualities of LAPET and its mortar were investigated. Specific gravity and unit weight of LAPET was very low in comparison with river sand like as 1.39, 844 kg/㎥ respectively. In addition, compressive strength of concrete significantly decreased because of specific gravity of aggregate decreased with increases in containing ratio. When LAPET was contained to 25% and 50％ of river sand, compressive strength of concrete at 28 days was indicated more 30MPa. Most of LAPET was generally showed to round shape and fluidity of mortar increased significantly due to sleeking the surface texture of LAPET. On the other hand, capillary absorption of mortar with LAPET was greatly increased in comparison with that of mortar without LAPET because of LAPET was composed of singular gradation. Absorption of LAPET was 0％ because the interior structure of LAPET consists of PET like as organic high polymer. Therefore the fault of normal lightweight aggregate, absorption, will be improved. It could expect several advantages that the pollution of environment will be previously prevent and the waste resources could be recycled if LAPET is reused as aggregate for Lightweight concrete.

• Magazine of the Korean Society of Agricultural Engineers
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• v.32 no.4
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• pp.71-80
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• 1990

Model tests for the ultimate pullout resistance of anchorages and investigation of failure behaviors in cohesionless soil have been conducted. The factors affecting the anchorage are mostly the geometry of the system, and soil properties of sands. The main conclusions of the experimental work were as follows. 1. The load - displacement relationship can be a form of parabolic curve for all plates. 2. The change in ultimate pullout resistance of anchor is mostly affected by embedment ratio and size of anchor, and influenced to a lesser degree by its shape. 3. Critical embedment ratio which is defined as the failure mode changes from shallow to deep mode is increased with increasing height of anchor. 4. For a constant anchor height, as the width of anchor increases the ultimate pullout resistance also increases. However, considering the efficiency of anchor for unit area, width of anchor does not appear to have any sigrnificant contribution on increasing anchor city. 5. Anchor capacity has a linear relation to sand density for any given section and the rate of change increases as the section increases. Critical depth determining the failure patterns of anchor is decreased with a decrease of sand density. 6. With increasing inclination angle, size of anchor, and decreasing embedment ratio, the ultimate pullout resistance of anchor under inclined loading is significantly decreased. 7. The ultimate pullout resistance of double anchor, a method of improving single of anchor capacity, is influenced by the center - to - center spacing adjacent anchors. It is also found that tandem and parallel anchor rigging arrangements decrease the anchor system capacity to less than twice the single anchor capacity due to anchor interference.

• Environmental Engineering Research
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• v.13 no.1
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• pp.1-7
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• 2008

Recently a new technology called the flexible-fiber deep-bed filter (FDF) claimed to replace the conventional sand filter including coagulation and sedimentation filter (CSF) processes in the water treatment plant. Therefore the life cycle assessment (LCA) approach was applied for evaluating the life cycle impacts of FDF compared with those of CSF. The used LCA softwares were the Simapro 6 and PASS and their life cycle impact assessment (LCIA) methodologies were the Eco-indicator 99 and the Korean Eco-indicator, respectively. The goal of this LCA was to identify environmental loads of CSF and FDF from raw material to disposal stages. The scopes of the systems have been determined based on the experiences of existing CSF and FDF. The function was to remove suspended solids by filtration and the functional unit was $1\;m^3$/day. Both systems showed that most environmental impacts were occurred during the operation stage. To reduce the environmental impacts the coagulants and electricity consumptions need to be cut down. If the CSF was replaced with the FDF, the environmental impacts would be reduced in most of the impact categories. The LCA results of Korean Eco-indicator and Eco- indicator99 were quite different from each other due to the indwelling differences such as category indicators, impact categories, characterization factors, normalization values and weighting factors. This study showed that the life cycle assessment could be a valuable tool for evaluating the environmental impact of the new technology which was introduced in water treatment process.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.631-642
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• 2010

This study is experimentally investigated for the characteristics of compression and tensile of lightweight air-trapped soils with uniform quality. Previously, EPS blocks are often used as lightweight embankment, but many problems such as the level difference and cracks caused by plastic(creep) deformation occurred in the EPS blocks. So, a new material development is urgent. By means of alternatives, lightweight air-mixed soil using in-situ soils has been developed and applied to fields. In comparison with EPS block, lightweight air-mixed soil have less creep deformation in long-time, but the strength characteristics of them are different depending on soils where they are obtained. Therefore, the quality management of them is very difficult. In this study, therefore, characteristics of lightweight air-trapped soil samples are investigated. To do this, the lightweight air-trapped soils are prepared using a manufactured sand with uniform quality. To found out the compression and tensile characteristics of lightweight air-tapped soils, unconfined compression test and splitting tensile test are conducted on the specimens prepared with different unit weight, cement-sand ratio and air-pore.

• Journal of the Korean Geotechnical Society
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• v.27 no.6
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• pp.81-95
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• 2011

This study investigates relative density test of standard sand and bottom ash which were devided into No.40, No.60, No.100, No.200 and resonant column tests were conducted for samples with the relative density of 40%, 55%, and 70% on the basis of the test results. Resonant column tests were also conducted for each residual bottom ash which contains the passing sample of No.200 with the relative density of 55%. By compressing each residual sample with the compaction energy of A-compact mold test, the passing percentage of No.200 sieve increased up to 30%, which led to the adjustment of relative density to 10%, 20%, and 30%. Test results show that maximum shear modulus and damping ratio of bottom ash are smaller than those of standard sand because crushing strength and unit weight of the former are smaller than those of the latter.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.142-149
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• 2003

Blind hydraulic backfilling is a commonly used technique for subsidence control of the strata over unapproachable waterlogged underground excavations. In this investigation model studies on all the three variants of this technique, namely, hydro-pneumatic or air-assisted gravity backfilling, pumped-slurry backfilling and simple gravity backfilling, have been carried out in fully transparent models of the underground excavations. On examination of the filling process, it was revealed that in all the three cases, the basic process of filling occurs by sand transport along one or more meandering channels. The relative influence of sand, water and air flow rates on the area of filling from a single inlet point and the hydraulic pressure loss per unit length were studied in details. In hydro-pneumatic backfilling process, the air bubbles while moving upward through the meandering channels provide an additional buoyant force over and above the available hydraulic head. In this way the area of filling from a single borehole may be quite large even at small flow rates of water. During actual field implementation the injected air, if not released completely from the rise side holes, may cause troubles by way of creating potholes on the surface. The pumped-slurry technique has shown its capability of filling a relatively larger area at faster rate, especially when high-volume, low-pressure method was selected. But simple gravity filling was also found to be equally effective method as slurry pumping, especially when flow rates were high. In the second and third method discussed above, examination of variations of injection pressure was also done and its relation with physical phenomenon was also attempted. Some empirical relationships were also developed using multivariate regression with a view to help the practicing engineers.

• Journal of the Korean GEO-environmental Society
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• v.14 no.2
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• pp.31-41
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• 2013

The dredged soils of western sea of Korea have been used as the fill materials because it possess the characteristics that constitute silt, silty sand and sand mainly. However, a study on dredged soils as the fill materials is insufficient. Hence, in this present study, the application the dredged soils of western sea of Korea as the fill materials was confirmed. Primary, the composition characteristics of the ground was analyzed to confirm the application on dredged soils as the fill materials by the piezo-cone penetration test. In laboratory test, it was performed the self-weight consolidation test for mechanical characteristics of the dredged soils. The direct shear test using self-weight consolidation test sample for shear strength characteristics was performed after self-weight consolidation test. Additionally, the mechanical characteristics of the dredged soils on elapsed time using self-weight consolidation test sample, which is drained naturally, was evaluated. The dredged soils of western sea of Korea show that unit weight and shear strength is increased as natural drain time elapses.