고강도 강관말뚝의 지지력 및 부마찰력 특성 분석

Abstract

For designing pile foundation, it is essential to accurately estimate the bearing capacity. However, a number of studies have reported that the reliability is extremely low of the estimation methods compared to the pile loading test. This study analyzed results of performed field load tests in order to estimate the best pile length and allowable bearing capacity of the pile foundation. Pile load tests and driving records, performed at Gwangyang, were used to evaluate the drivability and bearing capacity characteristics of STKT 590MPa grade high strength steel pipe (HSP) Piles. One type of piles varying in diameter and thickness were driven using a 16 and 13 ton hammer. Dynamic pile-driving formulae are widely used in predicting the load capacity of piles in soils. However, the accuracy of the formulae have been questioned for a long time due to their oversimplified assumptions and empirical parameters involved in the formulae. The allowable pile capacities calculated by 12 different dynamic pile driving formulae are compared statistically with the capacities measured in the field to find out the correlations between the calculated capacities and the measured values. The statistical data are then used to evaluate and to adjust the formulae to improve their accuracy. For the greatest accuracy and simplicity of use, it is recommended that the adjusted form of Hiley formula be used. In addition, the safety factors were compared and analyzed, for static formula method and dynamic formula method. The results of allowable bearing capacity by EOID test is in the range of 0.30∼7.63 compared to the capacity calculated by the Structure (HSP-1) Foundation Design Criterion. Allowable bearing capacity by restrike of pile dynamic loading test is in the range of 0.29∼7.4 compared to the Structure (HSP-1) Foundation Design Criterion. Based on the analyses of static load tests, the Chin's criterion is proved to be the most reasonable method for estimation of pile beariNg capacity among the methods used. The static bearing capacity formulae and the Meyerhof method using N values are applied to calculate the design bearing capacity of the piles. The resistance bias factors of the driven steel pipe piles are evaluated as 0.74 and 0.23, respectively, by comparison of the bearing capacities for both of the static bearing capacity formulae and the Meyerhof method. In addition, current method of predicting negative skin friction along the pile shaft in clay could overpredict the estimated capacity. Therefore, understanding the nature and behavior of negative skin friction along the pile shaft is absolutely essential.