Ohkyun Kwon

Comparison of the bidirectional load test with the top-down load test

For the past decade, the Osterberg testing method (O-cell test) has been proved advantageous over the conventional pile load testing method in many aspects. However, because the O-cell test uses a loading mechanism entirely different from that of the conventional pile loading testing method, many investigators and practicing engineers have been concerned that the O-cell test would give inaccurate results, especially about the pile head settlement behavior. Therefore, a bidirectional load test using the Osterberg method and the conventional top-down load test were executed on 1.5-m diameter cast-in-place concrete piles at the same time and site. Strain gauges were placed on the piles. The two tests gave similar load transfer curves at various depth of piles. However, the top-down equivalent curve constructed from the bidirectional load test results predicted the pile head settlement under the pile design load to be approximately one half of that predicted by the conventional top-down load test. To improve the prediction accuracy of the top-down equivalent curve, a simple method that accounts for the pile compression was proposed. It was also shown that the strain gauge measurement data from the bidirectional load test could reproduce almost the same top-down curve.

Horizontal Bearing Capacity of Suction Piles in Sand

A series of centrifuge model tests was conducted to measure the ultimate horizontal bearing capacity of suction piles. Three different pile lengths were tested in sand. Model piles were laterally loaded at different points along the pile length to evaluate the effect of the loading depth on the ultimate horizontal bearing capacity of suction piles. Two tests were conducted for each loading point. Results from centrifuge model tests were then compared with the analytical predictions to determine the validity of the analytical solution in predicting the ultimate horizontal bearing capacity of rigid suction piles loaded at various depths. Predicted values from the analytical solution compared well with the measured values from the centrifuge model tests.

Design Methodology on Steel-type Breakwater II. Pile Design Procedure

In this paper, the design procedure of substructure of the steel-type breakwater was described and the actual foundation design was performed for the test bed. The site investigation was executed at the Osan-port area, in Uljin, Gyeongbuk, where the steeltype detached breakwater is constructed. The foundation mainly depends on the lateral load and uplift force due to the wave force. Since the superstructure is stuck out about 9.0m from the ocean bed, the foundation must resist on the lateral force and bending moment. After considering various factors, the foundation type of this structure was determined by the steel pipe pile(). On the stability of pile foundation, the safety factors of the pile on the compressive, lateral and uplift forces were grater than the minimum factor of safety. The displacements of pile under the working load were evaluated as the values below the permissible ones. Based on the subgrade reaction method, we evaluated the relationship of subgrade reaction and displacement for the lateral and the vertical directions in the layers. The structural analyses along with the foundation were perfomed and the effect of pile foundations were compared quantitatively.

3-D NUMERICAL ANALYSIS OF A REPAIRED ROCK-SOCKETED BATTER PIPE PILE

Large diameter (D - 2,500 mm) batter steel pipe piles socketed into soft rock were constructed for the off-shore foundations of Kwangan grand bridge in Pusan, Korea. Concrete integrity tests so called cross-hole sonic logging tests were performed for mos of off-shore piles. Some of the rock-socketed piles were constructed during the initial stage of the project showed minor concrete defects, which were repaired with high pressure cement grouting. One pile had a severe defect near pile tip, which was repaired after three stages of grouting and non-destructive testing to check the repair. But three-dimensional numerical modeling and analysis was performed to check the quality of defect repairing and provide the reinforcement plan if the pile capacity was below the design load. As result of numerical analysis, the pile behaved primarily as a friction pile and most of applied external load was supported by friction resistance above the repaired rock-socket. Estimated bearing capacity (100 MN) of the pile was well larger than design load (24MM).