• Economic and Environmental Geology
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• v.53 no.5
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• pp.553-564
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• 2020

Transition between explosive and effusive eruption in Ulleung Island is observed in the Nari Scoria Deposits and Albong Trachyandesite (lava dome) origined by dome-building eruption and may be related to factors such as magma influx, ascent rate and degassing. However, the interpretation of them has not been resolved yet because the interaction between these factors is not complex but also the resulting behaviour during eruption is unpredictable. This paper focuses on the explosive and effusive activity perceived during building the Albong lava dome in Nari caldera. Samples were collected along with time from the scoria deposits and lava dome, linked to eruption stage and style of activity. Textures of groundmass feldspar microlites from these samples are quantitatively analyzed, including measurements of areal number density, mean microlite size, crystal aspect ratio, groundmass crystallinity and crystal size. The microlite textures show that shallow pre- and syn-eruptive magmatic processes acted to govern the changing behaviour during the eruption. Transition between explosive and effusive eruption was driven by the dynamics of magma ascent in the conduit, with degassing and crystallisation acting via feedback mechanisms, resulting in a cycle of effusive and explosive eruption.

• Journal of Korean Tunnelling and Underground Space Association
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• v.2 no.2
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• pp.50-61
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• 2000

The ground around the portal of a tunnel is the most typical part showing the 3-dimensional mechanical behavior in the tunnel. The portal slope is constructed at the weathered soft rock-mass, and remains as a potential sliding mass. The slope failure around the tunnel portal may happen drastically and induce the great disaster; hence, for the permanent stability several special techniques are required. To solve this problem, the ground around the tunnel portal may be excavated in the arch shape to develop the arching effect in horizontal direction. With the arch-type portal slope, one can reduce considerably the excavation mass and the damage of environments. This approach has not been attempted yet due to the lack of understanding and the well-defined analyzing method, so the retaining wall type portal is more universal. The 3-dimensional finite element analyses were carried out to prove that the arch type is more advantageous in safety and cost than the right angle type. The influence of the tunnel construction sequence and the strength of the rock-mass on the slope stability was investigated by focusing on the maximum shear strain in the slope, and the yield zone at the tunnel face.

• The Journal of Engineering Geology
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• v.23 no.3
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• pp.283-292
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• 2013

A calcareous rock slope failed during excavation of the slope for construction of a tunnel entrance. The slope is located at the construction site for widening highway in Yeongwol, Korea. Field surveys, laboratory tests, and numerical analyses were performed to determine the reason for the slope failure. The numerical analysis revealed that the safety factor of the slope before construction of the entrance was less than 1, and that this decreased after construction. After construction of the entrance, the sliding zone of the slope increased and slope stability decreased because the shear strain and plastic zone in the slope over the tunnel entrance showed an increase relative to the lower part of the slope. To enhance the stability of the slope for construction of the tunnel entrance, countermeasures such as rock bolts, rock anchors, and FRP (Fiber glass Reinforced Plastic) grouting were adopted in light of the field conditions. Serial field monitoring performed to confirm the reinforcing effects of the adopted countermeasures revealed a small amount of horizontal deformation of the slope soils, most of the elastic deformation that can regain its former value. In addition, the axial forces of the rock bolt and anchor were more strongly affected by slope excavation during construction of the tunnel entrance than by tunnel excavation or the rainy season, and the axial forces tended to converge after excavation of the tunnel. Therefore, we can confirm that the slope is currently safe.

• Journal of the Korean GEO-environmental Society
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• v.7 no.6
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• pp.13-22
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• 2006

The geotextile have been used in filtration and drainage for over 30 years in many applications of civil and environmental projects. Geotextile tube is compound technology of filtration and drainage property of geotextile. Geotextile have been used for various types of containers, such as small hand-filled sandbags, 3-dimensional fabric forms for concrete paste, large soil and aggregate filled geotextile gabion, prefabricated hydraulically filled containers, and other innovative systems involving containment of soils using geotextile. They are hydraulically filled with dredged materials. It have been applied in coastal protection and scour protection, dewatering method of slurry, and isolation of contaminated material. Recently, geotextile tube technology is no longer alternative construction technique but suitable desired solution. This paper presents the behavior of geotextile tube composite structure by 2-D limit equilibrium and plane strain analysis. 2-D limit equilibrium analysis was performed to evaluate the stability of geotextile tube composite structure for the lateral load and also the plane strain analysis was conducted to determine the design and construction factors. Based on the results of this paper, the three types of geotextile tube composite structure is stable. And the optimum tensile strength of geotextile is 151kN/m and maximum pumping pressure is 22.7kN/m.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.6
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• pp.95-102
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• 2015

Recently, the maintenance activity for aging of bridge structures was difficult because of traffic jam, environment pollution and increasing cost. And to solve these problems, modular bridge research has been studied. After static and cyclic loading test was conducted for serviceability and bending performance with one way slab, effective moment of inertia of modular specimen was analyzed to estimate the deflection by KCI(2012). To conduct the test, one integral slab and three modular slabs were made for static loading and one integral and modular slab were made for cyclic. As a result of the test, the modular slab had the similar bending performance of the integral. But the ultimate deflection showed the insufficient which was smaller than 20%. In the cyclic loading test, the modular slab has different behavior of deflection with the integral, so it was evaluated difficult for serviceability. In addition, effective moment of inertia by KCI(2012) was not estimated for modular slab with connection. The new value of m which was ratio between moments is 4.53 based on result of test for predicting deflection of modular.

• Journal of the Korean GEO-environmental Society
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• v.19 no.12
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• pp.41-46
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• 2018

The wireless sensor network system has the advantage of confirming the behavior of the entire facility by improving the disadvantages of conventional monitoring system. As a result, it is widely proposed as safety diagnosis and measurement of structures, water management systems, and management systems for dam structures. However, there is a lack of research that can evaluate the condition of facilities such as safety at the same time as monitoring. In this study, it is proposed a wireless sensor network system which can evaluate the behavior characteristics of facilities and evaluate the safety status for improving the technical disadvantages on conventional monitoring system. The geotechnical risk factors for the reservoir dam facility were evaluated and the limit values for the risk factors causing the failure of the facility were set. In other words, the system was set up so that the risk factors can be measured and the limit status can be evaluated immediately for each factor. In this study, numerical analysis is carried out for seepage and slope stability analysis using the typical cross section for reservoir dams. The stress-porewater coupling finite difference numerical analysis is performed for establishing the limit displacement for reservoir dam structures. It is developed a system that can estimate the time to reach the critical value by regression analysis using the measured datas.

• Journal of Korea Water Resources Association
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• v.51 no.spc
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• pp.1161-1169
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• 2018

In this study, a new methodology was proposed to evaluate the flood vulnerability of river levee and to investigate the effect on the levee where the water level changes according to climate change. The stability of levee against seepage was evaluated using SEEP/W model which is two-dimensional groundwater infiltration model. In addition to the infiltration behavior, it is necessary to analyze the vulnerability of the embankment considering the environmental conditions of the river due to climate change. In this study, the levee flood vulnerability index (LFVI) was newly developed by deriving the factors necessary for the analysis of the levee vulnerability. The size of river levee was investigated by selecting the target area. The selected levees were classified into upstream part, midstream part and downstream part at the nearside of Seoul in the Han river, and the safety factor of the levee was analyzed by applying the design flood level of the levee. The safety ratio of the levee was analyzed by applying the design flood level considering the current flood level and the scenario of climate change RCP8.5. The degree of change resulting from climate change was identified for each factor that forms the levee flood vulnerability index. By using the levee flood vulnerability index value utilizing these factors comprehensively, it was finally possible to estimate the vulnerability of levee due to climate change.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.1
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• pp.195-201
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• 2019

Long caisson breakwaters can improve the structural safety of a caisson due to the wave dispersion effect which reduces the average wave force acting on one caisson. However, in order to make long caissons, there are many manufacturing and construction limitations. Recently, interlocking caisson systems, which are to form a long caisson by interlocking individual caissons with adjacent caissons, have been much attention. In the present study, a interlocking caisson system with shear-keys was proposed and the wave dispersion effect according to the shear-key was evaluated analytically. As a result, (1) Because of the asymmetric shape of the interlocking caisson, the structure behavior and the wave dispersion effect of one are also asymmetric. (2) The wave dispersion effect is more influenced by the distribution and characteristics of wave acting on each caisson rather than the shape of the shear-key such as shear angle, height, shear length ratio. (3) The interlocking caisson breakwater is almost the same behavior and wave dispersion effect as a fully integrated breakwater.

• Journal of Korea Water Resources Association
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• v.54 no.7
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• pp.495-507
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• 2021

With the recent industrial development, accidental pollution in riverine environments has frequently occurred. It is thus necessary to simulate pollutant transport and dispersion using water quality models for predicting pollutant residence times. In this study, we conducted a field experiment in a meandering reach of the Sum River, South Korea, to validate the field applicability and prediction accuracy of RAMS+ (River Analysis and Modeling System+), which is a two-dimensional (2D) stream flow/water quality analysis program. As a result of the simulation, the flow analysis model HDM-2Di and the water quality analysis model CTM-2D-TX accurately simulated the 2D flow characteristics, and transport and mixing behaviors of the pollutant tracer, respectively. In particular, CTM-2D-TX adequately reproduced the elongation of the pollutant cloud, caused by the storage effect associated with local low-velocity zones. Furthermore, the transport model effectively simulated the secondary flow-driven lateral mixing at the meander bend via 2D dispersion coefficients. We calculated the residence time for the critical concentration, and it was elucidated that the calculated residence times are spatially heterogeneous, even in the channel-width direction. The findings of this study suggest that the 2D water quality model could be the accidental pollution analysis tool more efficient and accurate than one-dimensional models, which cannot produce the 2D information such as the 2D residence time distribution.

• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.89-99
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• 2006

The PCRW (Precast Concrete Retaining Wall) has many advantages compared with cast in place concrete retaining wall : shorter construction period, excellency of quality and minimum interference with the adjacent structure and traffics. However, shallow foundation type of PCRW, which has comparatively better ground condition, has some disadvantages such as difficulty in transportation and higher cost due to the size of PCRW being expanded by resisting only with self-weight if there is no other supplementary reinforcement. The presented study, in order to complement such disadvantages of PCRW, have applied the micropile method. The micropile method has advantages like low-cost and high-efficiency and does not require huge space, because it can be executed with small size equipment. However, the mechanical behavior characteristics of the PCRW reinforced by micropile, which is installed to improve the reinforcement effect, is not yet clearly identified and there is no suggested standard as to the length, diameter, install angle and install position of micropiles. Hence, this method is yet being designed depend on engineer's experience. In this study, various laboratory model tests as to sliding and overturning were performed in order to identify and present the optimum type of reinforcement and reinforcement effect of the PCRW reinforced by micropiles. In addition, it also executed numerical analysis for the purpose of verifying the optimum type of reinforcement for micropiles based on the results of laboratory model tests. The optimum reinforcement type of micropiles was estimated by model test and numerical analysis. The length of micropiles is 0.4 times wall height and the diameter is 0.04 times wall length.