Choong-Ki Chung

Optimal pile arrangement for minimizing differential settlements in piled raft foundations

This paper presents an optimal pile placement scheme to minimize the differential settlements of piled raft systems. A raft is modelled as a plate based on the Mindlin theory, and soils and piles are modelled as the Winkler springs and single springs, respectively. Interactions between piles are neglected. The pile spring constant is obtained by the method proposed by Randolph and Wroth, and the frmula is adopted to obtain the Winkler spring constant. The raft is discretized by isoparameteric finite element. The object function for the optimization is derived from the area of the deflected surface of a raft, and the locations of piles are selected as design variables. Inequality constraints are imposed to keep all piles completely inside of the raft. The recursive quadratic programming is adopted to minimize the nonlinear object function with respect to the design variables. The direct differentiation method is used to obtain the sensitivity of displacement. The validity and effectiveness of the proposed method are demonstrated by three numerical examples.

A Cell-permeable Fusion Protein for the Mineralization of Human Dental Pulp Stem Cells:

Human dental pulp stem cells (hDPSCs) are the only mesenchymal stem cells in pulp tissue that can differentiate into osteoblasts, odontoblasts, and adipose cells. The transcriptional co-activator with PDZ-binding motif (TAZ) protein has been reported to modulate osteogenic differentiation in mouse MSCs. Therefore, we examined whether the TAZ protein plays the same role in human pulp stem cells. In this study, TAZ was applied to cells directly with low-molecular-weight protamine (LMWP) as a cell-penetrating peptide (CPP). The LMWP-TAZ fusion proteins were expressed in an E. coli system with a pET-21b vector and efficiently transferred into hDPSCs without producing toxicity in the cells. The efficient uptake of TAZ was shown by Western blot with an anti-TAZ antibody, fluorescence-activated cell sorting, and confocal microscopy in live cells. The delivered TAZ protein increased osteogenic differentiation, as confirmed by alkaline phosphatase (ALP) staining, RT-PCR, and Western blotting. In addition, TAZ also inhibited adipogenic differentiation, regulating peroxisome proliferator-activated receptor-γ (PPAR-γ), lipoprotein lipase (LPL), and adipocyte fatty acid-binding protein (aP2) mRNA levels. These in vitro studies suggest that cell-permeable TAZ may be used as a specific regulator of hard-tissue differentiation.

Numerical assessment on the consolidation characteristics of clays from strain holding, self-boring pressuremeter test

Abstract The strain holding test (SHT), part of the self-boring pressuremeter test (SBPT), has been effectively utilized to determine the horizontal coefficient of consolidation ( c h ). However, the commonly used procedure proposed by Clarke et al. [Proc. 7th Eur. Comp. Soil Mech., Brighton 2 (1979) 207.] can lead to an erroneous estimation of c h , because of its simplified assumptions. This paper deals with numerical analyses based on realistic test conditions of the generally accepted testing procedure, and using the most commonly used type of pressuremeter. The effects of the pressuremeter geometry, the partial drainage during cavity expansion, and the cavity strain level for the holding test are investigated with the radial distribution of the initial excess pore pressure and its dissipation rate. Based on the results of the numerical analyses, the curve of the time factor for the 50% degree of consolidation ( T 50 ) needed to estimate c h is proposed with a modification method for soil permeability. Comparisons are made between c h values estimated from the SHT of the SBPT and those obtained from other in situ and laboratory tests performed at two sites in Korea. These results confirm the improved capability of the T 50 values proposed herein.

Consolidation test at constant rate of strain for radial drainage

A consolidometer for radial drainage under constant rate of strain (CRS) loading was developed. Theoretical solutions for determining the consolidation parameters, such as the coefficient of consolidation, compression index, recompression index, and preconsolidation pressure, from the test results were also proposed. Comparative experiments with CRS loading and incremental loading (IL) were carried out in radial drainage and also in vertical drainage. The results obtained from the developed CRS loading test agreed well with those of the conventional incremental loading test for radial drainage. They also showed that the CRS test enables the whole consolidation test to be completed in 2–6 h for commonly encountered fine grained soils.

Geo-spatial data integration for subsurface stratification of dam site with outlier analyses

A geo-spatial data integration method for three-dimensional subsurface stratification is proposed in this study. The proposed method integrates the boring data modified with the cross-validation based outlier detection method and the geophysical testing results using indicator kriging to offer the appropriate criteria of P-wave velocity, which are derived site specifically to classify the local geomaterials for dam site. Cross-validation for the outlier analysis of boring data is a test to evaluate the susceptibility of variogram models or kriging models and to reduce the statistical uncertainty of the boring data, and indicator kriging, the integration method, is characterized by geostatistical non-linear procedures to model the variability of spatial attributes. Using the integration method, the site-specific criteria of geomaterials are determined. The computer software is developed for the proposed method with ArcGIS developer tool and GSLIB. The results show that this proposed method presents more reliable stratification results than the conventional classification criteria.

Determination of Mean Shear Wave Velocity to the Depth of 30m Based on Shallow Shear Wave Velocity Profile

The mean shear wave velocity to the depth of 30 m (Vs30) derived from the western Vs is the current site classification criterion for determining the design seismic ground motion taking into account the site amplification potential. In order to evaluate the Vs30 at a site, a shear wave velocity (Vs) Profile extending to at least 30 m in depth must be acquired from in-situ seismic test. In many cases, however, the resultant depth of the Vs profile may not extend to 30 m, owing to the unfavorable field condition and the limitation of adopted testing techniques. In this study, the Vs30 and the mean shear wave velocity to a depth shallower, than 30 m (VsDs) were computed from the Vs profiles more than 30 m in depth obtained by performing various seismic tests at total 72 sites in Korea, and a correlation between Vs30 and VsDs was drawn based on the computed mean Vs data. In addition, a method for extrapolating the Vs profile from shallow depth to 30 m was developed by building a shape curve based on the average data of all Vs profiles. For evaluating the Vs30 from the shallow Vs profiles, both the methods using VsDs and shape curve result in less bias than the simplest method of extending the lowermost Vs equally to 30 m in depth, and are usefully applicable particularly in the cases of the Vs profiles extending to at least 10 m in depth.미국 서부 지역을 근간으로 도출된 30m 심도까지의 평균 전단파속도(Vs30)는 부지 증폭 정도에 따른 설계 지진 지반 운동 결정을 위한 현행 지반 분류 기준이다. 부지의 Vs30을 산정하기 위해서는 현장탄성파 시험으로부터 적어도 30m 심도까지의 전단파 속도(Vs) 분포를 획득해야 한다. 그러나 많은 경우에서 현장의 불리...

Application of statistical geo-spatial information technology to soil stratification in the Seoul metropolitan area

Typical geotechnical testing results reflect the level of soil uncertainty, which requires statistical corrections of the data for an appropriate engineering decision. This study proposes frameworks to detect outlying data points using statistical analyses, the cross-validation-based method and the generalised extreme value distribution-based method. The borehole data regarding soil depth distribution in a central area of Seoul, South Korea are assessed to validate the aforementioned methods for comparison with the distribution-based method and the Moran scatterplot method. The results show that the proposed methods enable more reliable spatial distributions to be achieved with a quantitative evaluation of local reliability.

The Influence of Dynamic Properties of Ground Soil on Vibration Characteristics of Rigid Body on Sand Ground

This study aims to investigate the influence of dynamic properties of the ground soil on vibration properties of a rigid body placed on the sand ground surface to clarify the vibration behavior of a structure in terms of the interaction between the structure and the ground. A series of cyclic triaxial tests and three types of model vibration tests were performed. The dynamic properties of ground soil were clarified using cyclic triaxial tests. It was found that the equivalent shear modulus markedly depends on confining pressure and relative density, and that the hysteresis-damping ratio also depends on confining stress but not upon relative density. In model vibration tests, rigid body models with variable masses, inertial moment, base size and base shape were prepared and their vibration behaviors were observed. Vibration characteristics were estimated from the observed behavior, and the period and damping ratio were examined. It was found that the period depends on not only the mechanical properties of the rigid body and the relative density of ground, but also upon the magnitude of the vibration amplitude. A simple model of a spring and a dashpot was used to correlate period and damping ratio of ground soil in a model vibration test with equivalent shear modulus and hysteresis damping ratio by cyclic triaxial testing. The relationship between normalized inverse squares of the period and rotation amplitude was similar to the relationship between the normalized equivalent shear modulus and the shear strain amplitude. Normalized damping ratio also showed good agreement with the normalized hysteresis-damping ratio. The calculated equivalent shear modulus from the simple model linearly increased with increased average contact pressure, as the equivalent shear modulus of the cyclic triaxial test 1 inearly increased with effective confining pressure on a log-log scale.

Integrated system for site-specific earthquake hazard assessment with geotechnical spatial grid information based on GIS

An integrated earthquake hazard assessment system with geotechnical spatial grid information was developed based on a geographic information system (GIS). The developed system, built, within the frame of GIS, consists of a database (DB) containing all available site information and processed data in the standard formats, and system software that performs various functions to manage and utilize the data in the DB. The system software is divided functionally into an input module, a geostatistical three-dimensional integration module, a real-time earthquake hazard assessment module, and an output or visualization module. A systematic framework for construction of a geotechnical spatial grid was developed to consider local site response characteristics for target areas. According to the framework, three interrelated assessment procedures were incorporated into the DB on a real-time basis: real-time seismic load determination, real-time liquefaction hazard estimation, and real-time structure fragility evaluation. The DB and these sub-modules of the system software were combined and integrated into a single system to provide a familiar and user-friendly working environment with a standard interface. In addition, the integrated system was imbedded into the Korea Integrated Seismic System server to be linked with real-time seismic accelerations, and a simulation of the system was specifically conducted at Incheon Port, Korea, using two actual earthquake events (the 2013 Baengnyeong and 2014 Taean earthquakes) and one virtual earthquake scenario. The simulation results were visualized as a geotechnical earthquake hazard map to verify the computer-aided real-time assessment framework at the times, when the three notable earthquake events occurred at the nearby Incheon Port.

A GIS-Based Framework for Real-Time Debris-Flow Hazard Assessment for Expressways in Korea

Debris flows caused by heavy rainfall in mountain areas near expressways lead to severe social and economic losses and sometimes result in casualties. Therefore, the development of a real-time system for debris-flow hazard assessment is necessary to provide preliminary information for rapid decision making about evacuations or restoration measures, as well as to prevent secondary disasters caused by debris flows. Recently, various map-based approaches have been proposed using multi-attribute criteria and assessment methods for debris-flow susceptibilities. For the macrozonation of debris-flow hazard at a national scale, a simplified method such as the Korea Expressway Corporation (KEC) debris-flow hazard assessment method can be applied for systematic analysis based on geographic information systems (GIS) and monitoring networks. In this study, a GIS-based framework of real-time debris-flow hazard assessment for expressway sections is proposed based on the KEC debris-flow hazard assessment method. First, the KEC-based method was standardized in a systematic fashion using ArcGIS, enabling the objective and quantitative acquisition of various attribute datasets. The quantification of rainfall criteria also was considered. A safety management system for debris-flow hazard was developed based on the GIS platform. Finally, the method was applied and verified on three expressway sections in Korea. The grading standard for each individual influencing attribute was subsequently modified to more accurately assess the debris-flow hazards.