• Tunnel and Underground Space
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• v.11 no.3
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• pp.257-269
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• 2001

Numerical simulation is performed to understand the structural behavior of an underground radwaste repository, assumed to be located at the depth of 500 m, in a granitic rock mats, in which a fault intersects the roof of the repository cavern. Two dimensional universal distinct element code, UDEC is used in the analysis. The numerical model includes a granitic rock mass, a canister with PWR spent fuels surrounded by the compacted bentonite inside the deposition hole, and the mixed bentonite backfilled in the rest of the space within the repository cavern. The structural behavior of three different cases, each case with a fault of an angle of $33^{\circ},\;45^{\circ},\;and\;58^{\circ}$ passing through the cavern roof-wall intersection, has been compared. And then fro the case with the $45^{\circ}$ fault, the hydro-mechanical, thermo-mechanical, and thermo-hydro-mechanical interaction behavior have been studied. The effect of the time-dependent decaying heat, from the radioactive materials in PWR spent fuels, on the repository and its surroundings has been studied. The groundwater table is assumed to be located 10m below the ground surface, and a steady state flow algorithm is used.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.1
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• pp.1-7
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• 2017

In general, the large loads which are applied from explosion, impact, earthquake and wind at a short time caused the materials of structures to large deformations, rotations and strains locally. If such phenomena will be analyzed, hydrocodes which can be considered fluid-structure interaction under computational continuum mechanics are inevitably needed. Also, the explosion mechanism is so complicated, it is reasonable that the behaviors of structure are predicted through explosion analyses and experiment at the same time. But, unfortunately, it is true that explosion experiments are limited to huge cost, large experiment facilities and safety problems. Therefore, in this study, it is shown that the results of explosion analyses using the AUTODYN are agreed with those of existing explosion experiments for reinforced concrete slabs within reasonable error limits. And the explosion damage of the same reinforced concrete slab are assessed for quite different reinforcement arrangement spacings, concrete cover depths, and vertical reinforcements. From the explosion analyses, it is known that the more the ratio of slab thickness to reinforcement arrangement spacing is increased, and small-diameter reinforcements are used than large-diameter reinforcements on the same reinforcement ratio, and vertical reinforcements are used, the more the anti-knock capacities are improved.

• Tunnel and Underground Space
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• v.26 no.3
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• pp.220-234
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• 2016

Sprayable waterproofing membrane has been considered as a substitute for a sheet waterproofing membrane in a variety of underground excavation works. However, fundamental properties of sprayble waterproofing membrane have not been fully given yet. In this study, a new two-component sprayable waterproofing membrane prototype was developed. In addition, its physico-mechanical properties were measured and compared with those of two kinds of thin spray-on liners where constitutive materials and construction methods are very close to each other. From direct tensile tests, the sprayable waterproofing membrane with elongations at break between 250% and 300% showed much higher ductility than TSLs. However, the sprayable waterproofing membrane had a limitation as a support member since its bond strength and loading capacity was lower than those of TSLs. From three-dimensional X-ray CT images, the porosity of the sprayable waterproofing membrane was estimated to be 26.13%. However, most of pores which might have been generated during membrane curing were not observed to be interconnected but isolated.

• Tunnel and Underground Space
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• v.29 no.4
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• pp.262-279
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• 2019

In the engineering barriers of high-level radioactive waste disposal, gases could be generated through a number of processes. If the gas production rate exceeds the gas diffusion rate, the pressure of the gas increases and gases could migrate through the bentonite buffer. Because people and the environment can be exposed to radioactivity, it is very important to clarify gas migration in terms of long-term integrity of the engineered barrier system. In particular, it is necessary to identify the hydro-mechanical mechanism for the dilation flow, which is a very important gas flow phenomenon only in medium containing large amounts of clay materials such as bentonite buffer, and to develop and validate new numerical approach for the quantitative evaluation of the gas migration phenomenon. Therefore, in this study, we developed a two-phase flow model considering the mechanical damage model in order to simulate the gas migration in the engineered barrier system, and validated with 1D gas flow modelling through saturated bentonite under constant volume boundary conditions. As a result of numerical analysis, the rapid increase in pore water pressure, stress, and gas outflow could be simulated when the dilation flow was occurred.

• Tunnel and Underground Space
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• v.31 no.5
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• pp.333-359
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• 2021

Gases such as hydrogen and radon can be generated around the canister in high-level radioactive waste disposal systems due to several reasons including the corrosion of metal materials. When the gas generation rate exceeds the gas diffusion rate in the low-permeability bentonite buffer, the gas phase will form and accumulate in the engineered barrier system. If the gas pressure exceeds the gas entry pressure, gas can migrate into the bentonite buffer, resulting in pathway dilation flow and advective flow. Because a sudden occurrence of dilation flow can cause radionuclide leakage out of the engineered barrier of the radioactive waste disposal system, it is necessary to understand the gas migration behavior in the bentonite buffer to quantitatively evaluate the long-term safety of the engineered barrier. Experimental research investigating the characteristics of gas migration in saturated bentonite and research developing numerical models capable of simulating such behaviors are being actively conducted worldwide. In this technical note, previous gas injection experiments and the numerical models proposed to verify such behaviors are introduced, and the future challenges necessary for the investigation of gas migration are summarized.

• Tunnel and Underground Space
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• v.31 no.1
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• pp.10-24
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• 2021

Rock mass classification for construction of underground facilities is essential to secure their stabilities. Therefore, the reliable values for rock mass classification from the precise information on rock discontinuities are most important factors, because rock mass discontinuities can affect exclusively on the physical and mechanical properties of rock mass. The conventional classification operation for rock mass has been usually performed by hand mapping. However, there have been many issues for its precision and reliability; for instance, in large-scale survey area for regional geological survey, or rock mass classification operation by non-professional engineers. For these reasons, automated rock mass classification using LiDAR becomes popular for obtaining the quick and precise information. But there are several suggested algorithms for analyzing the rock mass discontinuities from point cloud data by LiDAR scanning, and it is known that the different algorithm gives usually different solution. Also, it is not simple to obtain the exact same value to hand mapping. In this paper, several discontinuity extract algorithms have been explained, and their processes for extracting rock mass discontinuities have been simulated for real rock bench. The application process for several algorithms is anticipated to be a good reference for future researches on extracting rock mass discontinuities from digital point cloud data by laser scanner, such as LiDAR.

• Korean Journal of Materials Research
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• v.8 no.12
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• pp.1165-1169
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• 1998

A single crystal cast blade was manufactured by CMSX 6, one of the first generarion nickel based single crystal superalloys by the selector method in a vacuum furnace. The single crystal has been grown with cooling rate of 2.5 mm/min, after pouring the molten alloy of 163$0^{\circ}C$ to the mold heated to 150$0^{\circ}C$. The cast structure could be classified into matrix (dendrite) and eutectic regions in ${\gamma}$'shape and size. The eutectic region showed higher Ti content. As the additional results of ${\gamma}$'precipitates by EPMA and CBED analysis the ${\gamma}$'size was less than 0.5~0.7$\mu\textrm{m}$, showing the chemical composition close to Ni$_3$Al of Ll$_2$ lattice structure. But ${\gamma}$'size has increased to bigger than 1.0$\mu\textrm{m}$, being near to eutectic region, changing its shape to bar or huge block types. These showed the chemical structure near to Ni$_3$Ti of D $O_{24}$ lattice structure. Therefore, ${\gamma}$'morphology of dendrite and eutectic regions depends absolutely on its chemical composition and lattice structure.

• Journal of the Korean Institute of Landscape Architecture
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• v.46 no.4
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• pp.76-83
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• 2018

The purpose of this study is to analyze people who applied for and passed engineer landscape architecture examination that had been conducted from 2007 to 2016, the test frequency and trends by the question types in the landscape structure construction and management area, and the test tendencies and features by question types, and thereby to find the test trends for landscape structure construction and management in engineer landscape architecture examination. the analysis results are presented as follows: The people who applied for and passed engineer landscape architecture examinations that had been conducted from 2007 to 2016 were analyzed. as a result, the numbers of applicants and those who passed the examination have been on the decrease from 2011 and from 2012, respectively. the 10-year average rate of successful applicants for engineer landscape architecture examination was 11.2%. The test frequency and trends by the question types in the landscape structure construction area, and the test tendencies and features were analyzed. as a result, based on the key words in the seven categories (construction plan & process management, landscape materials, landscape planting foundation, work classification based construction, landscape estimation, basic structural mechanics, and survey), the questions about work classification based construction accounted for the largest, or 25.2%, and the questions about landscape planting foundation accounted for 3.3%. therefore, landscape planting foundation had lower test frequency and was less important than other categories. The test frequency and trends by the question types in the landscape management area, and the test tendencies and features were analyzed. as a result, based on the key words in the nine categories (operation and use & maintenance, pruning management, fertilization management, weed management, irrigation and drainage management, wintering management, pest management, and lawn management, and landscape facility management), the questions about operation and use & maintenance accounted for the largest, or 37.2%, and the numbers of the questions about fertilization management and irrigation & drainage management and of the questions about waterscape facility of landscape facility management have been on the increase from 2011 and from 2015, respectively. According to the analysis on the test tendencies for landscape structure construction and management areas in the examination there have been questions in a wide range and variety of categories. in terms of the landscape structure construction area, the frequency of questions in work classification based construction, landscape materials, and excellent quality in terms of the landscape management area, the frequency of questions in fertilization management, irrigation & drainage management, and waterscape facility of landscape facility management tends to increase because of environmental factors like climate change.

• Journal of the Korea Concrete Institute
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• v.16 no.1 s.79
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• pp.43-53
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• 2004

The current Korean Concrete Design Code(KCI Code) requires the minimum and maximum content of shear s in order to prevent brittle and noneconomic design. However, the required content of the steel reinforcement In KCI Code is quite different to those of the other design codes such as fib-code, Canadian Code, and Japanese Code. Furthermore, since the evaluation equations of the minimum and maximum shear reinforcement for the current KCI Code were based on the experimental results, the equations can not be used for the RC members beyond the experimental application limits. The concrete tensile strength, shear stress, crack inclination, strain perpendicular to the crack, and shear span ratio are strongly related to the lower and upper limits of shear reinforcement. In this research, an evaluation equation for the minimum content of shear reinforcement is theoretical proposed from the Wavier's three principals of the mechanics of materials.