• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.6A
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• pp.543-560
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• 2010

Safety-related concrete structures in a nuclear power plant must be protected against the impact of flying objects, referred to in the profession as missiles. In practice, the structural verification is usually carried out by means of empirical formulas, which relate the velocity of the impinging missile to the wall thickness needed to prevent scabbing or perforation. The purpose of this study is to reevaluate the predictability of the local effect prediction formulas for the penetration and scabbing depths and perforation thickness. Therefore, available formulas for predicting the penetration depth, scabbing thickness, and perforation thickness of concrete structures impacted by solid missiles are summarized, reviewed, and compared. A series of impact analyses is performed to predict the local effects of the projectile at impact velocities varing from 95 to 215 m/s. The results obtained from the numerical simulations have been compared with tests that were carried out at Kojima to validate numerical modelling. The simulation results show reasonable agreement with the Kojima test results for the overall impact response of the RC slabs. From these results, it seems that the Degen equation give a very good estimate of perforation thickness against a tornado projectile for test data. Finally, the results obtained from the impact analysis have been compared with Degen formula to determine the perforation thickness of the RC slab.

• Journal of the Korean Geotechnical Society
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• v.17 no.6
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• pp.99-110
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• 2001

Open-ended pipe piles are often used for the foundations of both land and offshore structures because of their relatively low driving resistance. In this study, load tests were performed on model pipe piles installed in calibration chamber samples in order to investigate the effects of pile installation method on soil plugging and bearing capacity. Results of the test program showed that the incremental filling ratio (IFR), which is used to indicate the degree of soil plugging in open-ended piles, decreased (i) with increasing hammer weight for the same driving energy and (ii) with increasing hammer weight at the same fall height. The base and shaft resistance of the piles were observed to increase (i) with increasing hammer weight for the same driving energy and (ii) with increasing hammer weight at the given same fa11 height. The jacked pile was found to be have higher bearing capacity than an identical driven pile under similar conditions, mostly due to the more effective development of a soil plug in jacking than in driving.

• Journal of the Korean Geotechnical Society
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• v.36 no.6
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• pp.17-34
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• 2020

In response spectrum analysis of pile-supported structure, an amplified seismic wave should be used as the input ground acceleration through the site-response analysis. However, each design standard uses different input ground acceleration criteria, which leads to confusion in determining the appropriate input ground acceleration. In this study, the ground accelerations were calculated through dynamic centrifuge model test, and the response spectrum analysis was performed using the calculated ground acceleration. Then, the moments derived from the test and analysis were compared, and a method for determining the appropriate input ground acceleration in response spectrum analysis was presented. Comparison of the experimental and simulated results reveals that modeling of the ground using elastic springs allows proper simulation of the natural period of the structure, and the use of a seismic wave that is amplified at the ground surface as the input ground acceleration provided the most accurate results for the response analysis of pile-supported structures in sands.

• Journal of the Korean Geotechnical Society
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• v.35 no.6
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• pp.27-38
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• 2019

Bearing capacity of a pile in homogeneous soil is the sum of end bearing and skin resistance, and the skin resistance is more prominent in sandy soil. Bearing capacity of a pile in pile groups especially in sandy ground should be designed under the consideration of the influence by the adjacent piles. In this study, the end bearing capacity of a pile in pile groups was experimentally investigated. For this purpose, piles were installed in sandy ground in a circular test box, and end bearing - settlement behavior of the pile was measured while the pile was loaded. As the results, end bearing - settlement relation curves of the piles showed a distinct limit value. Limit value of the end bearing was little affected by skin friction and pile diameter, and it became a constant value as pile penetrates deeper. End bearing was not affected by the adjacent piles in a group of piles, when their clearance was larger than the pile diameter.

• Journal of the Korean Geotechnical Society
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• v.22 no.9
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• pp.15-22
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• 2006

Single segmented mooring lines were tested in a geotechnical centrifuge for the purpose of calibrating the analytical solution developed for the analysis and design of various mooring lines associated with underwater drag/permanent anchors. The model mooring lines included steel ball chains and wire cables placed at various depths within the soft clayey seafloor soil. The mooring lines were loaded to preset tensions at the water surface under an elevated acceleration inside the centrifuge to simulate the field stress conditions experienced by the prototype mooring lines. This paper describes the calibration of two factors that are used as part of the input parameters in the analytical solution of mooring lines and considers the effect of chasing wires that were used in the experiment to determine the locations of the mooring lines.

• Journal of the Korean Geotechnical Society
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• v.23 no.1
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• pp.5-11
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• 2007

Micropiles have been used for underpinning or rehabilitation of existing foundations, and direct structural support system as well. However, relatively few studies have been done on the load-transfer mechanism of micropile systems in Korea. In addition to that, only the limited information is available for estimating the side friction values on micropiles installed in weathered soils. In this study, a full-scale test on an instrumented micropile is performed in order to establish the load-transfer curves based on a hyperbolic function. Then, an empirically derived equation that correlates the load-transfer curve of micropiles with the N values from field standard penetration tests is proposed. The results from all procedures are presented in this paper. Finally, back analysis using a finite difference method and the published field data are adopted for examination of a developed skin friction equation of micropile in weathered soils respectively.

• Journal of the Korean Geotechnical Society
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• v.24 no.10
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• pp.161-174
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• 2008

To investigate the characteristics of the shear wave velocity of cohesive soils and residual soils in Korea, Standard Penetration Test (SPT), Suspension PS Logging tests (SPS) and other soil tests were performed to analyze the shear wave velocity at each layer For these purposes, 2 study sites are selected: one is cohesive soils and the other is residual soils. As a results, new empirical formulas are proposed from the relationship between strength of the ground (N value) and shear wave velocity from the test data at each layer. In the case of cohesive soils, the proposed relationships are nearly similar to empirical formulas, however, in the case of residual soils there was a little difference between the empirical formulas and measured velocities in this study. Case examples for shear wave velocites are presented with depth, N-values and compared with Ohta et al. (1978) empirical formula.

• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.37-45
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• 2006

Bender elements, composed of thin piezo-ceramics and elastic shims, have been used to measure shear wave velocities of specimens in laboratories. In a preliminary stage of their field applications, an in-house research of optimizing suitable bender elements and their geometrical arrangement has been carried out in a barrel of kaolinite-water mixture. Two types of measurement configuration, similar to cross-hole and in-hole seismic testing, have been implemented. prototype instrumented rods were penetrated into a soft clay layer in the west coast and excellent shear waves were recorded. Development of penetration device (mandrel) and associated instrumented rods are in progress for deeper investigation.

• Journal of the Korean Geophysical Society
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• v.5 no.4
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• pp.293-303
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• 2002

Applying elastic plate model, we estimated elastic thickness and rigidity of the lithosphere in southern part of the Korean Peninsula($332km{\times}332km$ area of which center is $36.5^{\circ}N$ in latitude and $127.5^{\circ}E$ in longitude) by analysing terrain data and gravity data measured up to 2002. We tried to exclude the East Sea in choosing the study area because it has different tectonic environment. The mean Moho depth was estimated to be 30 km by power spectrum analysis of gravity data in the study area, Assuming one layer crust and applying elastic plate model, the loads with wavelengths of greater than 300 km are locally compensated, loads with wavelengths in the range 80-300km are partially supported by the strength of the lithosphere, and loads with wavelengths of less than 80km are almost completely supported by lithospheric strength. Assuming crustal model and rigidity, we calculated predicted coherence and compared it with observed coherence. As a result, we wert able to estimate the effective elastic thickness to be of 15 km(corresponding flexural rigidity is $3.0{\times}10^{22}Nm$). This indicates that the crust of the study area is relatively weaker than other old and stable continental regions but is similar to continental margins or oceanic area. The low rigidity could be explained by many tectonic and thermal activities such as orogenic activities, magmatic intrusions, volcanic activities, foldings, faultings, etc.

• The Korean Journal of Petroleum Geology
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• v.4 no.1_2 s.5
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• pp.20-26
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• 1996

In order to uncover the subsurface geological structure in the southwestern rim of the Ogcheon Fold Belt including the Cretaceous Neungju Sedimentary Basin, we analysed and interpreted the aeromagnetic anomalies over the region. The study area belongs to Muan-gun, Yeongam-gun, Gangjin-gun, Jangheung-gun, and eastem Haenam-gun. From the qualitative analysis and quantitative modeling of the reduced-to-the-pole magnetic anomalies, following things are revealed or suggested; Even though the porphyry of higher susceptibility is not crop out in the Donggang Myeon in the northwestern part of the study area, it is supposed to have intruded the Precambrian gneiss and the Cretaceous Bulgugsa granite of lower susceptibility. Two-dimemsional modeling of profile data across the sedimentary basin of Neungiu Group reveals that the northern part of the basin is deeper than the southern part, and that the maximum depth of the basin is supposed to be $3\cal{km}$ below the surface. The western flank of the basin bottom is steeper than the eastern flank. The high susceptibility value of the Neungju Group sedimentary rocks indicates that the rocks comprises large amount of volcanic materials. This fact implies that it is hard to expect hydrocarbon reservoir in the sedimentary rocks of the Neungiu Basin.