• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.142-149
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• 2019

In this study, the past erosion history and current status in the CHUNG-UI beach of Eulwang-dong, Jung-gu, Incheon-Si, South Korea were investigated and analyzed the wave with wave-induced current to investigate the causes of coastal erosion. As a result, the significant wave height ($H_{1/3}$) was in the range of 0.07~1.57 m and the mean value was 0.21 m. The maximum wave height ($H_{max}$) was in the range of 0.02-4.76m and the mean value was 0.27m. The vertical wave height and cycles were estimated through numerical model experiments of wave transformation. The 50-year frequency design wave height ranged from 0.82m to 3.75m. As a result of the experiment of wave-induced current, wave-induced current in the CHUNG-UI beach was decreased after the installation of the Detached breakwater and the Jetty. On the other hand, when the crest elevation was increased up to 5 m, there was no significant change, but when the crest elevation was increased to 8m, strong wave-induced current occurred around the submerged breakwaters due to lowered depth of water. In addition, the main erosion of the CHUNG-UI beach is due to the intensive invasion of the wave characteristics coming from the outer sea into the white sandy beach. The deformation of the wave centered on the front of the sandy beach caused additional longshore currents flowing parallel to the sandy beach and rip currents in the transverse direction, thus confirming that the longshore sediment was moved out of the front and out of the sea. The results of this study can be used as preliminary data for the recovery of the sand and the selection of efficient erosion prevention facilities.

• Journal of the Korean Geotechnical Society
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• v.34 no.12
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• pp.105-113
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• 2018

In this study, the engineering properties including bearing capacity of subgrades stabilized with a binder are analyzed by laboratory and field experiments. The main components of the binder are CaO and $SO_3$. After the binder was mixed with a low plasticity clay, the passing rates were relatively decreased as the sieve mesh size increased. Not only did the soil type change to silty sand, but engineering properties, such as the plasticity index and modified California bearing ratio (CBR), were improved for the subgrade. A comparison of the compaction curves of the stabilized subgrade and field soil compacted with the same energy demonstrated an increase of approximately 6% in the maximum dry unit weight, slight decrease in optimum moisture content, and considerable increase improvement in grain size. In the modified CBR test, the effect of unit weight and strength increase of the modified soil (with a specific amount of binder) was remarkably improved. As the proportion of granulated material increased after the addition of binder, the swelling was reduced by 3.3 times or more during initial compaction and 6.5 times by final compaction. The unconfined compressive strength of the specimens was maintained at the homogeneous value with a constant design strength. The stabilized subgrade was validated by applying it in the field under the same conditions; this test demonstrated that the bearing capacity coefficients at all six sites after one day of compaction exceeded the target value and exhibited good variability.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.5
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• pp.75-83
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• 2019

In order to fulfill the obligation to voluntarily reduce greenhouse gas emissions under the Paris Climate Agreement, the proportion of coal and nuclear power generation is reduced worldwide and national efforts are being made to spread renewable energy including solar power generation. Korea also intends to increase the proportion of renewable energy generation to 30~35% by 2040 by introducing laws and regulations. In addition, while the country is trying to apply solar power generation to sidewalks and roads, there is no research related to it in Korea. Therefore, as a precedent study to develop solar power generation roads, solar power generation concrete blocks applicable to sidewalks and plazas were developed and the applicability was evaluated by constructing them on the site. As a result of indoor experiment, compressive strength was measured by 25.5~35.7MPa and flexural strength was measured by 5.1~10.5MPa, which showed that all domestic standards were satisfied. However, the higher the unit cement amount, the lower the strength was measured according to the mixing of the broken fine aggregate. The absorption rate was 5.7%, which satisfied the domestic standard of 7% or less. As a result of the freeze-thawing test, the reduction rate of the compressive strength after 100 cycles was up to 6.3%. As a result of measuring the settlement amount after construction, the maximum of 2.498mm was measured and irregular settlement occurred in the overall area, which is because the resolution of the sand layer was poor during construction. Maintenance techniques of sidewalk concrete block and solar panel need to be established more efficiently through long-term operation in the further.

• Geophysics and Geophysical Exploration
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• v.22 no.3
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• pp.149-159
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• 2019

Borehole elemental concentration logging, measuring neutron-induced gamma rays by inelastic scattering and neutron capture interactions between neutron and formation, delivers concentrations of the most common elements found in the minerals and fluids of subsurface formation. X-ray diffraction and X-ray fluorescence analysis from core samples are traditionally used to understand formation composition and mineralogy, but it represents only part of formations. Additionally, it is difficult to obtain elemental analysis over the whole intervals because of poor core recovery zones such as fractures or sand layers mainly responsible for groundwater flow. The development of borehole technique for in situ elemental analysis plays a key role in assessing subsurface environment. Although this technology has advanced consistently starting from conventional and unconventional resources evaluation, it has been considered as exclusive techniques of some major service company. As regards domestic research and development, it has still remained an unexplored field because of some barriers such as the deficiency of detailed information on tools and calibration facility for chemistry and mineralogy database. This article reviews the basic theory of spectroscopy measurements, system configuration, calibration facility, and current status. In addition, this article introduces the domestic researches and self-development status on borehole elemental concentration tools.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.3
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• pp.330-337
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• 2021

3D printing is not only at the fundamental study and small-scale level, but has recently been producing buildings that can be inhabited by people. Buildings require a lot of cost and labor to work on the form work, but if 3D printing is applied to the building, the construction industry is received attention from technologies using 3D printing as it can reduce the construction period and cost. 3D printing technology for buildings can be divided into structural and non-structural materials, of which 3D printing is applied to non-structural materials. Because 3D printing needs to be additive manufacturing, control such as curing speed and workability is needed. Since cement mortar has a large shrinkage due to evaporation of water, cement polymer dispersion is used to improve the hardening speed, workability, and adhesion strength. The addition of polymer dispersion to cement mortar improves the tensile strength and brittleness between the cement hydrate and the polymer film. Cement mortar using polymer materials can be additive manufacturing but it has limited height that can be additive manufacturing due to its high density. When light-weight materials are mixed with polymer cement mortar, the density of polymer cement mortar is lowered and the height of additive manufacturing, so it is essential to use light-weight materials. However, the use of EVA redispersible polymer powder and light-weight materials, additional damage such as cracks in cement mortar can occur at high temperatures such as fires. This study produced a test specimen incorporating light-weight materials and EVA redispersible polymer powder to produce exterior building materials using 3D printing, and examined flame resistance performance through water absorption rate, length change rate, and cone calorimeter test and non-flammable test. From the test result, the test specimen using silica sand and light-weight aggregate showed good flame resistance performance, and if the EVA redispersible polymer powder is applied below 5%, it shows good flame resistance performance.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.12
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• pp.807-818
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• 2020

In this study, hydrophones using acoustic sensors were used to estimate the amount of bedload discharge in a forested watershed. The reaction characteristics were analyzed through hydrophone flume tests and field tests, and the quantitative bedload discharge was calculated and compared with that measured by a pit sampler. The hydrophone reaction changed the pulse according to the flow rate change, but did not react to standard sand. The pulse was different depending on the particle size and weight, and accordingly, there was a specific channel showing a suitable response. For a hydrophone installed in the field, by using an automatic impact device, the reaction characteristics of each channel were analyzed to confirm normal operation of the sensor and the suitability of the output value of each channel. In addition, a suitable channel was selected for the estimation of bedload discharge. The bedload discharge formula was developed using a hydrophone pulse and the average flow rate, and was compared with the measured data in the pit sampler in the study site. As a result of the study, if a hydrophone is used for monitoring the bedload in forested watersheds, it is considered effective in quantitatively estimating the weight of bedload discharge.

• Journal of Korean Society on Water Environment
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• v.37 no.6
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• pp.510-519
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• 2021

Volatile Organic Compounds (VOCs) in sediments, which can cause human health problems, have been monitored in Korea since 2014. Measured VOC concentrations can be affected by matrix type and the volatility of target substances. In this study, (1) VOCs volatility and the influence of matrix interference were confirmed, and (2) internal standards (IS) method was applied to improve analytical method. For these purposes, method detection limit (MDL), calibration linearity, precision and accuracy of VOCs were compared in various matrices using the IS. Some of VOCs in sediments showed different peak areas and reduced rates compared to water matrix. It was suggested that adsorption properties of sediments hindered the migration to vapor during heat pretreatment in headspace method. A calibration curve was created in clean sand. Recovery rates for the calibration curve method and IS applying method were 64.1~83.1% and 99.1~119.3%, respectively. Relative standard deviations ranged from 11.1% to 21.6% for the calibration curve method and those for IS ranged 4.7% to 13.7%. In case of real sediment, calibration curve and 1,2-Dichlorobenzene-d4 (ODCB) among IS were not suitable. The average recovery rate of Fluorobenzene (FBZ) increased by 56.4% and Relative Standard Deviation (RSD) by 4.7%. However, the recovery rate was increased in the samples with large values of igniting intensity. This study confirmed that influence of the matrix of VOCs in sediment, and addition of IS materials improved precision and accuracy. Although IS corrects volatilization and adsorption, it is recommended that more than two types of IS should be added rather than single.

• Journal of the Korean Geosynthetics Society
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• v.20 no.4
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• pp.1-7
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• 2021

In response to the carbon emission reduction trends and the depletion of natural sand caused by the use of cement in construction works, graphene oxide and porous feldspar were applied as countermeasures in this study. By using (3-aminopropyl)trimethoxysilane-functionalized graphene oxide with enhanced bond characteristics, a concrete specimen was prepared with 5% less cement content than that in a standard mortar mix, and the compressive strengths of the specimens were examined. The compressive strengths of the specimen with (3-aminopropyl)trimethoxysilane-functionalized graphene oxide and porous feldspar and the specimen with standard mixing were 26MPa and 28MPa, respectively, showing only a small difference. In addition, both specimens met the compressive strength of cement mortar required for geotechnical structures. It is believed that a reasonable level of compressive strength was maintained in spite of the lower cement content because the high content of pozzolans, namely SiO₂ and Al₂O₃, in the porous feldspar enhanced the reactions with Ca(OH)₂ during hydration, the nano-sized graphene surface acted as a reactive surface for the hydration products to react actively, and the strong covalent bonding of the carboxyl functional group increased the bonding strength of the hydration products.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.5
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• pp.355-374
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• 2022

Soil conditioning improves the performance of EPB (earth pressure balance) shield TBMs (tunnel boring machines) by reducing shear strength, enhancing workability of the excavated soil, and supporting the tunnel face during EPB tunnelling. The mechanical and rheological behavior of the excavated muck mixed with additives should be properly evaluated to determine the optimal additive injection condition corresponding to each ground type. In this study, the laboratory pressurized vane test apparatus equipped with a vane-shaped rheometer was developed to reproduce the pressurized condition in the TBM chamber and quantitively evaluate rheological properties of the soil specimens. A series of the pressurized vane tests were performed for an artificial sand soil by changing foam injection ratio (FIR) and polymer injection ratio (PIR), which are the injection parameters of the foam and the polymer, respectively. In addition, the workability of the conditioned soil was evaluated through the slump test. The peak and yield stresses of the conditioned soil with respect to the injection parameters were evaluated through the rheogram, which was derived from the measured torque data in the pressurized vane test. As FIR increased or PIR decreased, the workability of the conditioned soil increased, and the maximum torque, peak stress, and yield stress decreased. The peak stress and yield stress of the specimen from the laboratory pressurized vane test correspond to the workability evaluated by the slump tests, which implies the applicability of the proposed test for evaluating the rheological properties of excavated soil.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.40 no.5
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• pp.421-428
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• 2022

The earthwork is a core process of all constructions, and compaction measurement of earthwork play an important role in improving productivity. The analog tests such as Plate Bearing Test and Sand-cone occupy current compaction measurement techniques. Due to advanced 4th Industrial Revolution, research on analog tests combined smart construction technology are actively conducted. DCPT (Dynamic Cone penetration Test), simpler and faster than conventional tests, has recently on rise. However, it is also an analog that measures data manually and has several disadvantages such as history management and data verification. The IoT-based DCPT system developed in this study combines digital wire sensors, mobile phones, and Bluetooth with conventional DCPT. Compare to conventional test methods, IoT-based DCPT has advantages such as performance time, single-person measurement, low cost, mobile-based management, and real-time data verification. In addition, a test bed was built to verify IoT-based DCPT. The test bed was built under similar conditions to the actual earthworks site through roller equipment. DCPT data obtained from 322 stations. As a result, IoT-based DCPT showed good performance, and the test bed was also showed stable results as the compaction was carried out.