• Structural Engineering and Mechanics
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• 제60권5호
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• pp.809-828
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• 2016

In deep open pit mines, slope stability is very important. Particularly, increasing the depths increase the risks in mines having weak rock mass. Blasting operations in this type of open pits may have a negative impact on slope stability. Several or combination of methods can be used in order to enable better analysis in this type of deep open-pit mines. Numerical modeling is one of these options. Many complex problems can be integrated into numerical methods at the same time and analysis, solutions can be performed on a single model. Rock failure criterions and rock models are used in numerical modeling. Hoek-Brown and Mohr-Coulomb terms are the two most commonly used rock failure conditions. In this study, mine planning and discontinuity conditions of a lignite mine facing two big landslides previously, has been investigated. Moreover, the presence of some damage before starting the study was identified in surrounding structures. The primary research of this study is on slope study. In slope stability analysis, numerical modeling methods with Hoek-Brown and Mohr-Coulomb failure criterions were used separately. Preparing the input data to the numerical model, the outcomes of patented-blast vibration minimization method, developed by co-author was used. The analysis showed that, the model prepared by applying Hoek-Brown failure criterion, failed in the stage of 10. However, the model prepared by using Mohr-Coulomb failure criterion did not fail even in the stage 17. Examining the full research field, there has been ongoing production in this mine without any failure and damage to surface structures.

• Geomechanics and Engineering
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• 제19권2호
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• pp.167-178
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• 2019

Open-pit (OP) and underground (UG) mining are usually used to exploit shallow and deep ore deposits, respectively. When mine deposit starts from shallow subsurface and extends to a great depth, sequential use of OP and UG mining is an efficient and economical way to maintain mining productivity. However, a transition from OP to UG mining could induce significant rock movements that cause the slope instability of the open pit. Based on Yanqianshan Iron Mine, which was in the transition from OP to UG mining, a large-scale two-dimensional (2D) model test was built according to the similar theory. Thereafter, the UG mining was carried out to mimic the process of transition from OP to UG mining to disclose the triggered rock movement as well as to assess the associated slope instability. By jointly using three-dimensional (3D) laser scanning, distributed fiber optics, and digital photogrammetry measurement, the deformations, movements and strains of the rock slope during mining were monitored. The obtained data showed that the transition from OP to UG mining led to significant slope movements and deformations that can trigger catastrophic slope failure. The progressive movement of the slope could be divided into three stages: onset of micro-fracture, propagation of tensile cracks, and the overturning and/or sliding of slopes. The failure mode depended on the orientation of structural joints of the rock mass as well as the formation of tension cracks. This study also proved that these non-contact monitoring technologies were valid methods to acquire the interior strain and external deformation with high precision.

• Geomechanics and Engineering
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• 제34권5호
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• pp.547-559
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• 2023

We evaluated the applicability of machine learning techniques and the Kuz-Ram model for predicting the mean fragmentation size in open-pit mines. The characteristics of the in-situ rock considered here were uniaxial compressive strength, tensile strength, rock factor, and mean in-situ block size. Seventy field datasets that included these characteristics were collected to predict the mean fragmentation size. Deep neural network, support vector machine, and extreme gradient boosting (XGBoost) models were trained using the data. The performance was evaluated using the root mean squared error (RMSE) and the coefficient of determination (r²). The XGBoost model had the smallest RMSE and the highest r² value compared with the other models. Additionally, when analyzing the error rate between the measured and predicted values, XGBoost had the lowest error rate. When the Kuz-Ram model was applied, low accuracy was observed owing to the differences in the characteristics of data used for model development. Consequently, the proposed XGBoost model predicted the mean fragmentation size more accurately than other models. If its performance is improved by securing sufficient data in the future, it will be useful for improving the blasting efficiency at the target site.

• Steel and Composite Structures
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• 제38권1호
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• pp.79-86
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• 2021

Due to the complex geological conditions, a large number of high quality coal seams was buried in the western of China which cannot be mining in open-pit methods. The dynamic properties of that coal cannot be studied easily in real site for the complex working condition. The compound coal blocks made on the basis of the real situation were studied in the laboratory. The physical and mechanical properties of the compound coal blocks and the raw coal were contrasted by using the UCS tests. The results show that the compound coal blocks made by mixing coal powder, cement and water in proportion of 2.5:2:1 are the closest to that of standard raw coal. Then the propagation of strain waves and crushing effects on the coal were studied in the compound coal blocks by using the super dynamic strain test system and the numerical calculated method of ANSYS/LS-DYNA. The results show that the diameter of the crushing zone in the compound coal blocks was similar to that in the numerical results. The fractures distribution in laboratory tests also has a similar trend to the calculation results. The measured strain waves at the distance of 50 cm, 100 cm, and 150 cm from the center of the charge are mainly concerned at -1.0×104 με and have a similar trend as that in the numerical simulation.

• Asian-Australasian Journal of Animal Sciences
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• 제32권5호
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• pp.742-747
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• 2019

Objective: A concentration of airborne bacteria generated from swine houses is recognized to be relatively higher than other work places and it is essential to optimally manage it to prevent farmers' respiratory diseases. This study was conducted to assess the distribution characteristics of airborne bacteria in swine houses located at South Korea. Methods: A total 27 pig buildings of the enclosed type operated with mechanical ventilation system by a side wall fan and deep-pit manure system with slats were surveyed. Air samples were collected at 1.0 m above the middle floor in pig housing room. A six-stage viable particulate cascade impactor was used to identify the distribution of the sizes of particles in diameter. Results: Seasonal mean levels of airborne bacteria in the housing rooms of gestation/farrowing pigs, nursery pigs and growing/fattening pigs were 3,428(${\pm}1,244$) colony forming unit $(cfu)/m^3$, $8,325({\pm}3,209)cfu/m$, and $13,254({\pm}6,108)cfu/m^3$ for spring; $9,824({\pm}2,157)cfu/m^3$, $18,254({\pm}5,166)cfu/m^3$, and $24,088({\pm}9,274)cfu/m^3$ for summer; $1,707({\pm}957)cfu/m^3$, $4,258({\pm}1,438)cfu/m^3$, and $8,254({\pm}2,416)cfu/m^3$ for autumn; and $2,322({\pm}1,352)cfu/m^3$, $6,124({\pm}1,527)cfu/m^3$ and $12,470({\pm}4,869)cfu/m^3$ for winter, respectively. Conclusion: Concentrations of airborne bacteria according to pig housing type were highest in growing/fattening housing room followed by nursery housing room and gestation/farrowing housing room. In terms of seasonal aspect, the pig building showed the highest levels of airborne bacteria in summer followed by spring, winter and autumn. The respirable airborne bacteria which are ranged between 0.6 and $4.7{\mu}m$ accounted for approximately 60% compared to total airborne bacteria regardless of pig housing type.

• 대한소아치과학회지
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• 제37권4호
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• pp.488-496
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• 2010

치외치는 교합면에 법랑질이 원추형으로 돌출되어 결절을 형성한 치아로서, 치아발육 중 법랑기의 내측법랑상피가 외부로 과증식되거나 치수 간엽조직이 국소적으로 과증식되어 나타난다. 교합력이나 저작에 의해 파절 또는 마모되기 쉬우며 따라서 이로 인하여 치수노출에 의한 감염이 야기될 수 있다. 상악 전치부 설면에도 원추형으로 돌출된 결절이 관찰되기도 하는데 이를 탈론 교두(talon cusp)라 한다. 치내치는 치아 발육 중 설측의 법랑상피가 일부 함입되어 설측에 깊은 소와가 형성된 형태로서 크기나 전체적인 모양은 정상이다. 방사선 사진상에서 치경부의 법랑질 일부가 함입되어 함입강을 형성하고 그 기저부는 치수에 가까이 위치하고 있어 치수와 개통되어 있을 가능성도 있다. 탈론 교두(talon cusp)와 치내치는 비교적 흔한 형태 이상이지만, 한 치아에 동시에 발생하는 경우는 매우 드물다. 이러한 환자에서 탈론 교두(talon cusp)가 교합력이나 저작에 의해 파절되거나, 교두 사이 열구가 우식에 이환되어 치수치료가 시행 될 때, 치내치의 복잡한 근관 형태로 인해 많은 어려움이 있다. 따라서 교합조정, 치면열구전색술 등의 예방적 처치와 주기적인 검진이 필요하고, 치수치료시 정확한 방사선학적 진단을 통한 치내치의 근관 형태 파악이 필요하다. 조선대학교 치과병원 소아치과에 내원한 10세 남아(하악 좌측 중절치)와 8세 여아(상악 우측 중절치) 그리고 7세 남아(상악 우측 중절치)에서 치내치를 동반한 탈론 교두(talon cusp)가 관찰되어 본 증례를 보고하고자 한다. 9세 남아와 8세 여아는 치수 병변으로 인해 치수 치료 중이고, 7세 남아는 병적 소견 없이 교합조정 후 관찰 중이다.