• Explosives and Blasting
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• v.40 no.3
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• pp.19-32
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• 2022

Hydrogen is a fuel having the highest energy compared with other common fuels. This means hydrogen is a clean energy source for the future. However, using hydrogen as a fuel has implication regarding carrier and storage issues, as hydrogen is highly inflammable and unstable gas susceptible to explosion. Explosions resulting from hydrogen-air mixtures have already been encountered and well documented in research experiments. However, there are still large gaps in this research field as the use of numerical tools and field experiments are required to fully understand the safety measures necessary to prevent hydrogen explosions. The purpose of this present study is to develop and simulate 3D numerical modelling of an existing hydrogen gas station in Jeonju by using handheld LiDAR and Ansys AUTODYN, as well as the processing of point cloud scans and use of cloud dataset to develop FEM 3D meshed model for the numerical simulation to predict peak-over pressures. The results show that the Lidar scanning technique combined with the ANSYS AUTODYN can help to determine the safety distance and as well as construct, simulate and predict the peak over-pressures for hydrogen refueling station explosions.

• Explosives and Blasting
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• v.41 no.4
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• pp.1-8
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• 2023

On August 4, 2020, 2750 tons of ammonium nitrate stored in a storage warehouse at the Port of Beirut exploded. This explosion is said to be the largest ammonium nitrate explosion ever. By applying the TNT equivalency method, TNT equivalent amount corresponding to the explosion energy of 2750 tons of ammonium nitrate was calculated, and it is found to be 856 tons. Overpressure and impulse were calculated in a range up to 3600 m from the blast using the Kingery-Bulmash explosion parameter calculator tool. As the distance from the explosion center increases, the overpressure and impulse decrease exponentially, but the overpressure decreases more significantly, showing that overpressure is more affected by distance than the impact. As a result of applying the damage criteria to evaluate the effects of overpressure and impulse on the structure, the critical distances at which partial collapse, major damage, and minor damage to the structure occur are found to be approximately 500, 800, and 2200 m from the center of the explosion, respectively. The probit function was applied to evaluate the probability of damage to structures and human body. The points where the probability of collapse, major damage, minor damage, and breakage of window-panes to structures are greater than 50% are found to be approximately 500, 810, 2200, and 3200 m, respectively. For people within 200 m from the center of the explosion, the probability of death due to lung damage is more than 99%, and the 50% probability of eardrum rupture is approximately 300 m. The points with a 100% probability of death due to skull rupture and whole body impact due to whole body displacement are evaluated to be 300 and 100 m, respectively.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.744-751
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• 2006

In case of the Soil Nail System applied to a slope, effects of vibrations from blasting, earthquake and creep of long term behaviors cause reductions of adhesion between grout and soil-nail. There are some reports of nail's pull-out failure by those reasons. In this paper it is suggested that the Cone Nailing System is enable to diminish effects of vibrations and creep. In this study on Cone Nailing System, the cones are installed to each nail by 2m. By such installing cones, the adhesion between nail and grout will increase and the long term creep behavior will decrease. In this study, the centrifuge test is performed to understand the behaviors of the Cone Nail System. For the centrifuge test, the soil tank is 52cm in width, 17cm in length and 35cm in height. In comparison with general soil nail, the centrifuge test of general soil nail(without cone) is performed equally. Additionally, the interface between cone nail and soil through the pull-out test is applied to FLAC 2D version 3.3. and the evaluation of application for the Cone Nail System in slope is performed.

• Geomechanics and Engineering
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• v.37 no.1
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• pp.49-64
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• 2024

Rocks undergoing repeated loading and unloading over an extended period, such as due to earthquakes, human excavation, and blasting, may result in the gradual accumulation of stress and deformation within the rock mass, eventually reaching an unstable state. In this study, a CNN-CCM is proposed to address the mechanical behavior. The structure and hyperparameters of CNN-CCM include Conv2D layers × 5; Max pooling2D layers × 4; Dense layers × 4; learning rate=0.001; Epoch=50; Batch size=64; Dropout=0.5. Training and validation data for deep learning include 71 rock samples and 122,152 data points. The AI Rock Constitutive Model learned by CNN-CCM can predict strain values(ε₁) using Mass (M), Axial stress (σ₁), Density (ρ), Cyclic number (N), Confining pressure (σ₃), and Young's modulus (E). Five evaluation indicators R², MAPE, RMSE, MSE, and MAE yield respective values of 0.929, 16.44%, 0.954, 0.913, and 0.542, illustrating good predictive performance and generalization ability of model. Finally, interpreting the AI Rock Constitutive Model using the SHAP explaining method reveals that feature importance follows the order N > M > σ₁ > E > ρ > σ₃.Positive SHAP values indicate positive effects on predicting strain ε₁ for N, M, σ₁, and σ₃, while negative SHAP values have negative effects. For E, a positive value has a negative effect on predicting strain ε₁, consistent with the influence patterns of conventional physical rock constitutive equations. The present study offers a novel approach to the investigation of the mechanical constitutive model of rocks under cyclic loading and unloading conditions.

• Journal of Periodontal and Implant Science
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• v.39 no.3
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• pp.293-301
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• 2009

Purpose: The purpose of this study is to show the total survival rate of implants with maxillary sinus floor elevation and the effects that reach the survival rate by classifying types of graft materials, implant surface, operation method, bone height. Methods: In a total of 131 patients, 251 implants with sinus floor elevation were installed simultaneously or after regular healing. Various bone grafts (autograft, xonograft, allograft, alloplast) and implant surface (MTX-HA implant, chemical etching implant, Titanium oxide surface implant, resorbable blasting media implant, resorbable blast texturing implant, HA-coated implant) were used. All implants were investigated clinically and radiographically, being with 1 to 5 years follow-up period after installation. Results: The survival rate of 251 implants with maxillary sinus floor elevation was 94%. The types of implant, surface, graft material, bone height have no statistically signi-ficant differencies. Conclusions: It can be suggested that maxillary sinus floor elevation may have predictable result with various bone graft materials and implant surface.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.33 no.3
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• pp.241-248
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• 2011

Purpose: The aim of this study was to present the clinical results of maxillary sinus augmentation implants and to evaluate the effects of various factors on the implant survival rate. Methods: In a total of 112 patients, 293 implants after sinus augmentation were performed. The total survival rate and the influence of the following factors on implant survival were evaluated; patient characteristics (sex, age, smoking, general disease), graft material, implant surface, implant installation stage, site of implant placement, length and width of implant, closure method for osseous window, residual alveolar bone height. Results: 1. Age ranged from 16 to 70 yr, with a mean of 45.7 yr. 2. Cumulative survival rate for the 293 implants with the maxillary sinus augmentation procedure was 94.9%. 3. Simultaneous implant installation was performed in 122 patients and delayed implant installation was performed in 117 implants. The average healing period after sinus elevation was 7.3 months for delayed implant installation and this procedure had a significantly higher survival rate. 4. There were no significant differences in sex, age, smoking, general disease, site of implant placement, length and width of implant, residual alveolar bone height and the survival rate. 5. RBM (Resorbable Blasting Media) implant surface and allograft groups had significantly lower survival rates. Conclusion: These data suggest that maxillary sinus augmentation may give more predictable results for autogenous bone grafts and delayed implant placement.

• Tunnel and Underground Space
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• v.9 no.4
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• pp.315-327
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• 1999

Rock fracture mechanics has been widely applied to blasting, hydraulic fracturing, rock slope and many other practical problems in rock engineering. But a measuring method for the fracture toughness of rock, one of the mort important parameters in fracture mechanics as an intrinsic property of rock, has not been yet well established. To obtain mode I rock fracture toughness, the more favorable disc-typed specimens such as CCNBD, SCB, chevron-notched SCB and BDT were used in this study. Rock fracture toughness under mixed-mode and mode II conditions was measured by using the STCA applied to the CCNBD specimen. Size effects such as specimen thickness, diameter and notch length on fracture toughness were investigated. From the mixed-mode results, fracture envelops were obtained by applying various regression curves. The mixed-mode results were also compared with three mixed-mode failure criteria. In each fracture toughness test, acoustic emission was measured to get the data for determining the load levels of different crack propagation patterns.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.30 no.5
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• pp.417-427
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• 2008

The aim of this study is to investigate the effect of anodizing surface to osseointegration of implant by using of resonance frequency analysis (RFA), quantitative and qualitative assessment of an anodically modified implant type with regard to osseous healing qualities. A total of 96 screw-shaped implants were prepared for this study. 72 implants were prepared by electrochemical oxidation with different ways. 24 (group 1 SP) were prepared at galvanostatic mode in 0.25M sulfuric acid and phosphoric acid. 24 (group 2GC) were prepared at galvanostatic mode in calcium glycerophosphate and calcium acetate and 24 (group 3 CMP (Calcium Metaphosphate) Coating were prepared at galvanostatic mode in 0.25M sulfuric acid and phosphoric acid followed by CMP coating. Rest of 24 (control group were as a control group of RBM surface. Bone tissue responses were evaluated by resonance frequency analysis (RFA) that were undertaken at 2, 4 and 6 weeks after implant placement in the mandible of mini-pig. Group 1 SP (anodized with sulfuric acid and phosphoric acid implants) demonstrated slightly stronger bone responses than control Group RBM. Group 2 GC (anodized surface with calcium glycerophosphate and calcium acetate implants) demonstrated no difference which were compared with control group. Group 3 GMP (anodized and CMP coated implants) demonstrated slightly stronger and faster bone responses than any other implants. But, all observation result of RF A showed no significant differences between experimental groups with various surface type. Histomorphometric evaluation demonstrated significantly higher bone-to-implant contact for group 2 GC. Significantly more bone formation was found inside threaded area for group 2 GC. It was concluded that group 2 GC (anodized surface with calcium glycerophosphate and calcium acetate implants) showed more effects on the bone tissue responses than RBM surface in initial period of implantation. In addition, CMP showed a tendency to promote bone tissue responses.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.1
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• pp.1-15
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• 2008

Recently, because of the various factors by uncertainty of underground, the risks in tunnelling have been occurred increasingly. Therefore, it is very important to estimate and control the risks considering geotechnical conditions for tunnel stability and environmental problems by tunnel construction. In this study, the risk analysis for tunnel stability was carried out by classifying the risk factors such as ground support capacity, ground settlement, the inflow of groundwater into the tunnel and the damage by the earthquake. Also, the risk assessment for the environmental problems was performed by calculating the vibration and noise by blasting and the drawdown of the groundwater level caused by tunnel construction. Each risk factor was evaluated quantitatively based on the probabilistic and statistic technique, then it was analyzed the distribution characteristic along overall tunnel site. Finally, it was evaluated that how much each risk factor influences on the construction cost with a period for tunnel construction, so it is possible to perform reasonable tunnel design which was capable of minimizing the risks in the tunnel construction.

• Journal of the Korean GEO-environmental Society
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• v.24 no.5
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• pp.5-12
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• 2023

Recently, due to urban development and expansion, construction plans have been increasing adjacent to existing tunnel structures such as subways, roads, and large pipelines. Structural plans adjacent to existing tunnels have different effects on tunnel stability depending on the construction method, degree of proximity, and location of new structures. In particular, the pressure water tunnel shows a very large difference from other road tunnels and railway tunnels in geotechnical characteristics and operation characteristics. Therefore, it is necessary to review the safety zone due to adjacent construction in consideration of the geotechnical characteristics of the water tunnel and the new sturure construction method. In this study, the existing tunnel safety zone standards were investigated. A stability evaluation performed numerical analysis considering the deterioration of concrete lining in operation and the characteristics of water tunnel. In addition, the impact of vibration caused by pile construction and blasting excavation of new structures was reviewed. Based on this, a pressure water tunnel safety zone was proposed in consideration of adjacent construction.