• The Journal of Engineering Geology
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• v.33 no.4
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• pp.599-609
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• 2023

In the seismic retrofitting of harbor breakwaters in Korea, the recovery rate is often uncertain due to site conditions and site conditions, and problems continue to arise. Therefore, in this study, we analyzed the recovery rate and compressive strength of the improved material through drilling survey by grouting confirmation method after applying low-fluidity mortar injection method, and furthermore, we checked the elastic modulus by downhole test and tomography to confirm the reinforcement effect of soft ground after ground improvement. The experimental results showed that the average shear wave velocity of the ground increased from 229 m/s to 288 m/s in BH-1 and BH-3 boreholes to a depth of 28.0 m, and the average shear wave velocity of the ground to a depth of 30.0 m tended to increase from 224 m/s to 282 m/s in the downhole test. This is believed to be a result of the increased stiffness of the ground after reinforcement. The results of the tomographic survey showed that the Vs of the soft ground of the sample at Site 1 increased from 113 m/s to 214 m/s, and the Vs of the sample at Site 2 increased from 120 m/s to 224 m/s. This shows that the stiffness of the ground after seismic reinforcement is reinforced with hard soil, as the Vs value satisfies 180 m/s to 360 m/s in the classification of rock quality according to shear wave velocity.

• The Journal of Engineering Geology
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• v.33 no.4
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• pp.573-586
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• 2023

Joints or weak planes can induce anisotropy in the strength and deformability of fractured rock masses. Comprehending this anisotropic behavior is crucial to engineering geology. This study used plaster as a friction material to mold specimens with a single joint. The strength and deformability of the specimens were measured in true triaxial compression tests. The measured results were compared with three-dimensional numerical analysis based on the distinct element method, conducted under identical conditions, to assess the reliability of the modeled values. The numerical results highlight that the principal stress conditions in the field, in conjunction with joint orientations, are crucial factors to the study of the strength and deformability of fractured rock masses. The strength of a transversely isotropic rock mass derived numerically considering changes in the dip angle of the joint notably increases as the intermediate principal stress increases. This increment varies depending on the dip of the joint. Moreover, the interplay between the dip direction of the joint and the two horizontal principal stress directions dictates the strength of the transversely isotropic rock mass. For a rock mass with two joint sets, the set with the steeper dip angle governs the overall strength. If a rock bridge effect occurs owing to the limited continuity of one of the joint sets, the orientation of the set with longer continuity dominates the strength of the entire rock mass. Although conventional three-dimensional failure criteria for fractured rock masses have limited applicability in the field, supplementing them with numerical analysis proves highly beneficial.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.4
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• pp.9-14
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• 2022

Silica aerogel is a porous material with a very low density and high specific surface area. Still, its application is limited due to its weak mechanical properties due to structural features. To solve this problem, a method of complexing it with various polymers has been proposed. We synthesized polyimide cross-linked silica aerogel by the sol-gel process to obtain high mechanical properties. Tetraethyl orthosilicate (TEOS) was used as a precursor to make silica aerogel, and 3- aminopropyltriethoxysilane (APTES) was used as a coupling agent for cross-linking polyimide. Polyimide was synthesized using pyromellitic dianhydride and 3,5-diaminobenzoic acid, and mechanical properties were improved by crosslinking polyimide with 10 repeating units in the polyimide chain using the reaction formula ${\frac{n_1}{n_2}}={\frac{n}{n+1}}$ To realize silica aerogel, polyimide having various weight ratios was added before gelation, resulting in a 19-fold or greater increase in maximum compressive strength compared to pure silica aerogel. From this study, an enhancement of silica aerogel could be enhanced through polymer cross-linking bonds.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.70-78
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• 2023

The ordinary concentrically braced frame has an advantage of having simple design procedure. For this reason, it has been widely used for the small-sized frame structures subject to moderate or lower magnitude earthquake, even though its seismic performance against the earthquake load is not much effective compared to that of other frame systems. To enhance seismic performance of the ordinary concentrically braced frame where the bracing has a weakness for compressive behavior under lateral earthquake, seismic retrofitting by viscous damper has been commonly introduced. However, the viscous damper, itself, generally does not have stiffness for restoring the structure to the original position. This may cause residual displacement to the structure. In this paper, a self-centering viscous damper system in which upper and lower beams having flexural rigidity play a role as a nonlinear-elastic spring, restoring the spring-damper system subject to external displacement history to its original location, is developed. The numerical analysis for a simplified frame structure shows how including the developed self-centering viscous damper system leads to an enhanced seismic performance of the frame structure through energy dissipation during earthquake excitation.

• Tunnel and Underground Space
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• v.33 no.6
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• pp.594-609
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• 2023

TBM (Tunnel Boring Machine) method is gaining popularity in urban and underwater tunneling projects due to its ability to ensure excavation face stability and minimize environmental impact. Among the prominent models for predicting disc cutter life, the NTNU model uses the Cutter Life Index(CLI) as a key parameter, but the complexity of testing procedures and rarity of equipment make measurement challenging. In this study, CLI was predicted using multiple linear regression analysis and tree-based machine learning techniques, utilizing rock properties. Through literature review, a database including rock uniaxial compressive strength, Brazilian tensile strength, equivalent quartz content, and Cerchar abrasivity index was built, and derived variables were added. The multiple linear regression analysis selected input variables based on statistical significance and multicollinearity, while the machine learning prediction model chose variables based on their importance. Dividing the data into 80% for training and 20% for testing, a comparative analysis of the predictive performance was conducted, and XGBoost was identified as the optimal model. The validity of the multiple linear regression and XGBoost models derived in this study was confirmed by comparing their predictive performance with prior research.

• Tunnel and Underground Space
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• v.33 no.6
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• pp.519-533
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• 2023

In this study, the linear cutting tests of pick cutters were carried out on a granitic rock with the average compressive strength over 100 MPa. From the tests, the correlation between the cutter acting force and the temperature measured by infrared thermal imaging camera during rock cutting was analyzed. In every experimental condition, the maximum temperature was measured at the rock surface where the chipping occurred, and the temperature generated in the rock was closely correlated with the cutter acting force. On the other hand, the temperature of a pick cutter increased up to only 36℃ above the ambient temperature, and the correlation with the cutter force was not obvious. This can be attributed to the short cutting distance under laboratory conditions and the high thermal conductivity of the tungsten carbide inserts. However, the relatively high temperature of the tungsten carbide inserts was found to be maintained. Therefore, it is recommended that a reinforcement between the insert and the head of a pick cutter or the quality improvement of silvering brazing in the production of a cutter is necessary to maintain the high cutting performance of a pick cutter.

• Journal of the Korean Geosynthetics Society
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• v.23 no.2
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• pp.63-75
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• 2024

Drinking water is an essential element to ensure the basic human right to live, and the quality of clean water must always be ensured. However, domestic water facilities, which were installed intensively in the early 2000s, are deteriorating. The accidents such as discoloration of water such as chromaticity and turbidity as well as leakage of substances frequently occur. However, since it is virtually impossible to replace all water pipes, the detailed standards for maintenance of water pipe network facilities established in 2021 require water pipe cleaning. The swab pig method, one of the water pipe cleaning methods, is a method of physically removing substances in pipes and is evaluated as having the highest cleaning efficiency. However, Swab is highly likely to be damaged or deformed during the cleaning process, and may even be lost. Therefore, in this study, the material of the pig was changed to a material with high compressibility, and it was made as close as possible to the inner wall of the water pipe. And, to maximize cleaning efficiency, a rotation swab pig with a rotation blade was developed. In addition, high-strength wire and winding equipment were additionally developed to eliminate the possibility of loss and to determine the location of the pig. The inlet and outlet are connected with wires, and after verifying the performance of each detailed technology, the technology was applied on a test bed with a 30m section. As a result of the application, the performance of the technology was verified by measuring the process time and evaluating applicability.

• Journal of the Korean Geotechnical Society
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• v.40 no.3
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• pp.93-100
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• 2024

Pore water freezes in low-temperature compaction, which leads to different compaction characteristics compared to room temperature conditions. In regions like Alberta, Canada, where organic soils are prevalent, compaction performance is influenced by the high water retention and compressibility of organic soils, as well as their sensitivity to freezing and thawing. Alberta's strict environmental regulations demand the reuse of excavated soil for backfill, and the long winter season creates challenging conditions for civil engineering projects. In this study, a laboratory compaction test was conducted to evaluate the low-temperature compaction characteristics of organic soils with varying organic content. The results indicate that the optimum moisture content increases as the organic content increases, and the maximum dry unit weight decreases by up to 21.9%. In addition, under temperature conditions below -4℃, no optimum moisture content was observed, and the dry unit weight decreased as the moisture content increased.

• Journal of the Korean Geosynthetics Society
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• v.23 no.2
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• pp.53-62
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• 2024

Recently, development of non-traditional energy such as oil sands has been actively conducted in the cold region such as Canada. Frozen soil has different thermal and mechanical characteristics from general soil due to its high organic contents. This study evaluated the impact of organic matter content on the thermal and mechanical behavior of frozen soil samples collected from Alberta, Canada, and Gangwon Province, South Korea. As the organic content increases, the maximum dry unit weight decreases and the optimum moisture content increases in compaction tests. In uniaxial compression tests under frozen conditions, the strength of the frozen specimens increased as the temperature decreased. The strength of Canada soil sample increased with higher organic matter content at low temperatures. However, the strength of frozen soil was not significantly affected by organic matter content due to the complex behavior and unfrozen water content. Thermal conductivity tests showed higher thermal conductivity in frozen conditions compared to unfrozen conditions, due to the higher thermal conductivity of ice compared to water. These findings provide essential data for geotechnical design and construction in large-scale projects such as oil sands development in cold regions. Further research is needed to explore the impact of organic matter content on different types of frozen soils.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.30 no.1
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• pp.63-72
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• 2024

Poly (butylene adipate-co-terephthalate) (PBAT) is one of the representative biodegradable polymers with high ductility and processability to replace petroleum-based polymers. Many investigations have been conducted to broaden the applications of PBAT in a variety of industries, including the food packaging, agricultural mulching film, and logistics and distribution fields. Foaming process is widely known technique to generate the cell structure within the polymer matrix, offering the insulation and light weight properties. However, there was no commercially feasible foam product based on biodegradable polymers, especially PBAT, and maintaining a proper melt viscosity of the polymer would be a key parameter for the foaming process. In this study, chemical foaming agent and cross-linking agent were introduced to PBAT, and a compression molding process was applied to prepare a foam sheet. The correlation between cell morphological structures and mechanical and physical properties was evaluated. It was found that PBAT with foam structures effectively reduced the density and thermal conductivity, allowing them to be suitable for applications such as insulation and lightweight packaging or cushion materials.