Chung-Won Lee

Development of Prebored Screw Pile Method and Evaluation of Its Bearing Characteristics

The pile-driving method produces considerable noise and vibrations. Hence, an auger-drilled pile method was developed as a low-noise and -vibration substitute. However, this method does not guarantee the bearing capacity of the pile unless some amount of pile-driving is performed. Therefore, the noise and vibration problems cannot be completely solved. In this study, a prebored screw pile method is proposed to solve these problems. In this method, piles are constructed by the rotary penetration of a screw pile into a prebored hole filled with some cement milk and whose diameter is smaller than that of the screw pile. To determine the shape of the screw pile, laboratory tests with model screw piles were conducted. Also, field load tests were conducted on an actual screw pile fabricated based on the laboratory test result and on a smooth-surfaced pile. In addition, the behavior of the screw pile was estimated by using three-dimensional finite element analysis. The results of the field load test and the numerical simulation showed that the ultimate bearing capacity and the unit skin friction of the screw pile are very superior to those of the smooth-surfaced pile and the cement milk is an important factor in the prebored screw pile method.

Influence of Damaged Geosynthetic Mat to Dredged Sea Sand Fill inside a Tide Embankment

In order to investigate the behavior of dredged sea sand fill compacted inside tide embankments with damaged geosynthetic mat, centrifugal model tests were conducted with sea level variations. Results of vertical displacements, investigation by observation and excavation, and image analysis from the three centrifugal model tests considering particle size conditions of rubble mound and filter layers, and damage of geosynthetic mat were examined. The results demonstrate that the subsidence of the dredged sea sand fill inside tide embankments with the damaged geosynthetic mat was strongly affected by the loss of dredged sea sand into the filter layers for large filter particles and by a decrease in the bearing capacity of the filter layers for small filter particles.

A Study on Pore Water Pressure Behavior of Fill Dam with Water Level Raising using Centrifugal Model Tests

The aim of this study is to examine the behavior of reservoir fill dam with the water level raising by use of the centrifugal model test and the numerical simulation. In this study, LIQCA2D-SF based on the cyclic elasto-plastic constitutive model proposed by Oka et al. (1999) is applied for numerical simulation. In order to investigate the displacements and the pore water pressures in the fill dam due to the water level raising velocity, three model tests in centrifugal field of 50g for fill dams were conducted. A comparison between the test result and the simulation result has provided the influence on the displacement and the pore water pressure of the fill dam with increasing up of the water level.

Engineering Properties of Volcanic Ash-Cement Soil Mixtures and Zeolite-Cement Soil Mixtures

In this study, the engineering characteristics of volcanic ash-cement soil mixtures and zeolite-cement soil mixtures are investigated by using unconfined compression test, freezing-thawing test, SEM and XRD analysis. The samples were mixed with volcanic ash from Mt. Baekdusan or porous zeolite, and cement as the ratios of 3.5:1, 4.0:1, 4.5:1, 5.0:1 with and without metakaolin. It is confirmed that compressive strength degraded with increasing of the amount of volcanic ash or zeolite, and increased with addition of metakaolin as a binder. Moreover, test results suggested that the mixtures provided sufficient freezing-thawing resistance. In addition, ettringite as a product of cement hydration was detected by SEM and XRD, and that possibly contributes to the strength of the mixtures.

The behavior characteristics of a reservoir levee subjected to increasing water levels

AbstractCentrifugal model testing has been widely used to study the stability of levees. However, there have been a limited number of physical studies on levees where the velocity of increasing water levels was considered. To investigate the behavior characteristics of reservoir levees with different velocities of increasing water levels, centrifugal model tests and seepage-deformation coupled analyses were conducted. Through this study, it was confirmed that increasing water levels at higher velocities induces dramatic increases in the displacement, plastic volumetric strain and risk of hydraulic fracturing occurring in the core of the levee. Hence, real-time monitoring of the displacement and the pore water pressure of a levee is important to ensure levee stability.

Loss with Time of Dredged Sea Sand in Tidal Embankment Subject to Sea Level Variation

In this study, loss with time of dredged sea sand in a tidal embankment subject to sea level variation was examined through the centrifugal model test. The experimental results demonstrate that a differential subsidence occurs on the surface of the dredged-sea-sand fill and that the largest subsidence was observed just above the damaged portion of the geosynthetic mat. In addition, image analysis provided the largest displacement vector at the damaged portion of the geosynthetic mat, the shear-strain localization from the damaged portion of the geosynthetic mat through the center of the slope surface, and the crest of the dredge-sea sand fill. These displacement vectors and shear strains occurred early in the experiment and increased over time. Therefore, the loss of dredged sea sand can occur rapidly with damage to the geosynthetic mat and can possibly induce differential subsidence and cracks at the surface of the dredged-sea sand fill.

Stability Study of a Tide Embankment Subjected to Sea Level Variations Using Centrifugal Model Tests

To investigate the behavior of dredged-sea-sand fill compacted inside tide embankments with a damaged geosynthetic mat, centrifugal model tests and numerical simulation were conducted, both considering variations in sea level. The results from the three centrifugal model tests demonstrate that the subsidence of the dredged-sea-sand fill inside tide embankments with a damaged geosynthetic mat was strongly affected by the loss of dredged-sea-sand into the filter layers with large particles and a decrease in the bearing capacity of the filter layers with small particles. In addition, a comparison of the test and simulation results confirms that the loss of sand into the filter layer and the subsidence of the dredged-sea-sand fill were well reproduced by the numerical simulation.

Numerical Simulation on Seepage and Seismic Behaviors of Poorly-Compacted Raised Reservoir Levee

It is urgent to redevelop the superannuated reservoir levee through the levee raising for countermeasure to climate change and improvement of storage capacity of reservoir. However, low compaction degree of the raised reservoir levee owing to poor construction condition leads to degradation of the stability of the reservoir levee on seepage and earthquake. In this study, seepage and seismic behavior of raised reservoir levee with low compaction degree was evaluated through numerical simulation. From the simulated results, water level raising possibly induces crack and/or sinkhole on the surface of the poorly-compacted raised reservoir levee owing to the increase of the subsidences at the crown and the front side of that. In addition, relatively larger displacement and acceleration response at the front side of raised reservoir levee in seismic condition may degrade overall stability of reservoir levee. Therefore, reasonable construction management for the compaction of the raised reservoir levee is required for ensuring long-term stability on seepage and earthquake.

Determining Method of Risk-Weighted Value for Applying to Individual Insurance Rate on Storm and Flood Damage

The storm and flood insurance is currently growing as a national disaster management insurance against natural disasters. In current storm and flood insurance rate system, however, weighted rates for the sources of natural disasters (flood, wind, snow etc.) are not only considered, but also single insurance rate is applied to a total of 229 cities and districts without considering regional risks. In the present study, therefore, different insurance rates according to the sources of natural disasters, reflecting regional risks, were estimated and finally reasonable weighted rates were proposed based on the estimated results.

Studies on Behavior Characteristics of Raised Reservoir Levee Using Centrifugal Model Test

This study aims to investigate the behavior of raised reservoir levee via centrifugal model test. The experimental results demonstrate that the overflow failure occurred at crown, at a part of front side and at rear side of the original reservoir levee, while, the stability of the raised reservoir levee was ensured at the same water level although the subsidence of crown of the raised levee due to the water level raising was larger than that of the original levee. Thus, it is significant to redevelop the superannuated reservoir levee through the levee raising for countermeasure to climate change and storage capacity improvement of reservoir. In addition, the real-time monitoring of pore water pressures and displacements is required to ensure the levee`s stability.