• Journal of the Korean Geotechnical Society
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• v.21 no.5
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• pp.187-196
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• 2005

Since the allowable bearing capacities of piles in weathered/fractured rock are mainly governed by settlement, the load-displacement behavior of pile should be known accurately. To predict pile head settlement at the design stage, the exact understanding of the load-transfer mechanisms is essential. Therefore, in this research, the load-transfer mechanism of drilled shaft socketed into weathered rock was investigated. For the investigation, five cast-in-place concrete piles with diameters of 1,000 mm were socketed into weathered gneiss. The static axial load tests and the load-transfer measurements were performed to examine the axial resistant behavior of the piles. A comprehensive field/laboratory testing program on weathered rock at the Held test sites was also performed to describe the in situ rock mass conditions quantitatively. And then, the effect of rock mass condition on the load transfer mechanism was investigated. The f-w (side shear resistance-displacement) curve of the pile in moderately weathered rock reached to yielding point at a for millimeter displacements, and after yielding point, the rate of resistance increment dramatically decreased. However, the f-w curve in the highly/completely weathered rock did not show the obvious yielding point, and the resistance gradually increased showing the hyperbolic pattern until relatively high displacement (>15 mm). The q-w (end bearing resistance-displacement) curves showed linear response at least until the base displacement of approximately 10 mm, regardless of rock mass conditions.

• Tunnel and Underground Space
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• v.32 no.5
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• pp.312-326
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• 2022

The generalized Hoek-Brown (GHB) criterion, which is recognized as one of the standard failure conditions for rock mass, is specialized for rock engineering applications and covers a wide range of rock mass conditions. Accordingly, many research efforts have been devoted to the incorporation of this criterion into the stability analysis of rock structures. In this study, the slip-line analysis method, which is a kind of elastoplastic analysis method, is combined with the GHB failure criterion to derive analytical equations that can easily calculate the plastic radius and stress distribution in the vicinity of the circular tunnel. In the process of derivation of related formulas, it is assumed that the behavior of rock mass after failure is perfectly plastic and the in-situ stress condition is hydrostatic. In the formulation, it is revealed that the plastic radius can be calculated analytically using the two respective tangential friction angles corresponding to the stress conditions at tunnel wall and elastic-plastic boundary. It is also shown that the plastic radius and stress distribution calculated using the derived analytical equations coincide with the results of Lee & Pietruszczak's numerical method published in 2008. In the latter part of this paper, the influence of the quality of the rock mass on the size of the plastic zone, the stress distribution, and the change of the tangential friction angle was investigated using the derived analytical equations.

• The Journal of Engineering Geology
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• v.33 no.4
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• pp.519-530
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• 2023

Moye's analytical solution was examined as a method for constant-head tests under steady-state conditions, and results were compared with transient-state analyses in in situ hydraulic tests. The sensitivity of hydraulic conductivities calculated using Moye's method increased with the length of the test section, which should be as large as possible under test conditions. Particularly in low-permeability media with less than 10^-8 m/sec of hydraulic conductivity, hydraulic conductivity is lower than that under transient-state conditions and can be recalculated by adjusting the boundary between radial and spherical flow assumed in Moye's equation. Constant-head tests performed in the research borehole at the KAERI Underground Research Tunnel (KURT) indicated that transmissivities derived from the constant-head withdrawal test under transient-state conditions in low-permeability media were higher than those derived from steady-state tests, likely because the groundwater flow boundary was smaller than the "half of the test-section length"assumed by Moye's equation. When interpreting constant-head test results for crystalline rock, the hydrogeological properties of the medium may be better understood by considering assumed conditions accompanying analysis of the steady-state condition and comparing them with results for the transient-state analysis, rather than simply assuming properties based on steady-state analyses.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.5
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• pp.285-291
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• 2014

The statistical information of the coastal water temperature monitoring data can be biased because of outliers and missing intervals. Though a number of outlier detection methods have been developed, their applications are very limited to the in-situ monitoring data because of the assumptions of the a prior information of the outliers and no-missing condition, and the excessive computational time for some methods. In this study, the practical robust method is developed that can be efficiently and effectively detect the outliers in case of the big-data. This model is composed of these two parts, one part is the construction part of the approximate components of the monitoring data using the robust smoothing and data re-sampling method, and the other part is the main iterative outlier detection part using the detailed components of the data estimated by the approximate components. This model is tested using the two-years 5-minute interval water temperature data in Lake Saemangeum. It can be estimated that the outlier proportion of the data is about 1.6-3.7%. It shows that most of the outliers in the data are detected and removed with satisfaction by the model. In order to effectively detect and remove the outliers, the outlier detection using the long-span smoothing should be applied earlier than that using the short-span smoothing.

• Korean Journal of Remote Sensing
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• v.35 no.6_3
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• pp.1197-1208
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• 2019

Wildfire is a major natural disaster affecting socioeconomics and ecology. Remote sensing data have been widely used to estimate the wildfire danger with an advantage of higher spatial resolution. Among the several wildfire related indices using remote sensing data, Temperature Vegetation Dryness Index (TVDI) assesses wildfire danger based on both Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature (LST). Although TVDI has physical advantages by considering both weather and vegetation condition, previous studies have shown TVDI does not performed well compare to other wildfire related indices over the Korean Peninsula. In this study we have attempted multiple modification to improve TVDI performance over the study region. In-situ measured air temperature was employed to increase accuracy, regression line was generated using monthly data to include seasonal effect, and TVDI was calculated at each province level to consider vegetation type and local climate. The modified TVDI calculation method was evaluated in wildfire cases and showed significant improvement in wildfire danger estimation.

• Journal of the Korean Geosynthetics Society
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• v.17 no.3
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• pp.1-8
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• 2018

Sand compaction pile (SCP) is a ground improvement method which is used to secure the stability of the soft ground by using a type of replacement pile filled with coarse grained material. The behavior characteristics of the SCP, which is frequently used for improving both the onshore and offshore ground, is governed by the ground condition, the installation method, and replacement ratio. Therefore, the stability of the SCP in terms of the bearing capacity and displacement needs to be evaluated considering both the design values and in-situ conditions of construction site. In this study, numerical analysis is carried out based on the conditions of 00 revetment construction site in South Korea where unexpected displacement occurred during construction of SCP. Based on the analysis results, the displacement of the revetment structure according to the replacement ratio of the SCP was compared to the result calculated from design formulas. The results showed that the lateral displacement can be exceeded the reference value from proposed criteria regardless of increased replacement ratio of SPC. It is also confirmed that the behavior of the structure according to the replacement ratio of SPC in not reflected in the existing calculation methods. Therefore, the stability of the SCP composite ground should be examined through the site inspection after the SCP construction.

• The Journal of Engineering Geology
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• v.27 no.4
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• pp.475-487
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• 2017

We performed landslide flume tests to analyze characteristics of landslide occurrence and change in the ground materials due to rainfall infiltration. The test apparatus is composed of flume, rainfall simulator, and measurement sensors and landslides were triggered by heavy rainfall (Intensity=200 mm/hr) sprinkled at the above of an artificial slope. The measurement sensors for matric suction and volumetric water content were installed with 3 sets at shallow (GL-0.2 m), middle (GL-0.4 m), and deep depth (GL-0.6 m) in the slope and the tests were performed with in-situ, loose, and dense condition of each weathered soils of granite, gneiss, and mudstone. The analyses show that surface erosion was dominant in initial time of the test due to heavy rainfall and then landslides occur following locally happened transverse tension cracks. The characteristics of landslide were both shallow failure because of a spread of wetting front induced by the rainfall infiltration and retrogressive failure. While the matric suction was decreased rapidly without any precursor in the soil saturation, the volumetric water content was increased gradually, reached its maximum value, and then decreased rapidly with landslide.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.17 no.6
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• pp.523-528
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• 1984

The small filefish, Rudarius ercodes, generally spawning from mid May to early October in the natural habitat, was exposed to various photoperiod and temperature regimes. These environmental effects on the gonad activity, regression and recrudescence were experimentally investigated based on the mechanism of reproductive cycle. Spawning season was initiated in the early spring with the gonad activated by long photoperiod(13L) and stimulated by compensatory temperature rising. Even when the gonad activated readily at the above critical daylength (12L to 13L)was kept back at the below if, it went on maturing. At the end of spawning period (mid September), since the shortening of daylength (12L) resulted in the gonad regression regardless of temperature, the short daylength might be related to the termination of spawning in situ. When the regressive gonad at the post spawning period was treated by the above 13L: $20^{\circ}C$ condition, it could recrudesce and bring forth even spawning. From this fact, the feasible control of annual reproductive cycle of small filefish was recognized. But even in the long daylength, the temperature above $28^{\circ}C$ was preventive of gonad maturation.

• Journal of the Korean Geotechnical Society
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• v.31 no.5
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• pp.35-46
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• 2015

In this study, the behavior of self-supported earth retaining wall with stabilizing piles was investigated by using a numerical study and field tests in urban excavations. This earth retaining wall can provide stable support against lateral earth pressures through its use of stabilizing piles that provide passive resistance to lateral earth pressures arising due to ground excavations. Field tests at two sites were performed to verify the performance of instrumented retaining wall with stabilizing piles. Furthermore, detailed 3D numerical analyses were conducted to provide insight into the in situ wall behavior. The 3D numerical methodology in the present study represents the behavior of the self-supported earth retaining wall with stabilizing piles. A number of 3D numerical analyses were carried out on the self-supported earth retaining wall with stabilizing piles to assess the results stemming from wide variations of influencing parameters such as the soil condition, the pile spacing, the distance between the front pile and the rear pile, and the pile embedded depth. Based on the results of the parametric study, the maximum horizontal displacement and the maximum bending moment significantly decreased when the retaining wall with stabilizing piles is used. Moreover, the horizontal displacement reduction effect of influencing parameters such as the pile spacing and the distance between the front pile and the rear pile is more sensitive in sandy soil, with a higher friction angle compared to clayey soil. In engineering practice, reducing the pile spacing and increasing the distance between the front pile and the rear pile can effectively improve the stability of the self-supported earth retaining wall with stabilizing piles.

• Journal of Korean Society of Environmental Engineers
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• v.37 no.12
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• pp.705-711
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• 2015

Degradation of 2,6-Dichlorophenol (DCP) using liquid ferrate(VI) synthesized by wet oxidation method has been studied. Several parameters such as pH (acid, base and neutral), DCP initial concentration, ferrate dosage, and temperature have been examined to determine the optimal experimental conditions. The ferrate(VI) has useful properties such as strong oxidizing power and selectivity and generates a non-toxic end product, Fe(III). Ferrate ion reduced rapidly to Fe(III) and oxygen in acidic and neutral conditions. The experimental results showed the higher DCP degradation efficiency in the neutral condition than in the acidic and basic conditions. The oxidation of DCP strongly depended on the dosage of ferrate added to the reactor and DCP initial concentration. With increasing of ferrate dosage the degradation efficiency of DCP increased, while the degradation efficiency of DCP decreased with increasing of DCP initial concentration. The effect of temperature has been tested at 4 different levels (10, 25, 35, and $50^{\circ}C$). The optimal temperature was obtained in $25^{\circ}C$ and degradation efficiency decreased as the temperature increased in the range from $25^{\circ}C$ to $50^{\circ}C$. The DCP degradation pathways were studied and proposed based on the intermediate products identified by GC/MS analysis.