RELIABILITY BASED LOAD TRANSFER CHARACTERISTICS OF BORED PRECAST PILES EQUIPPED WITH GROUTED BULB IN THE PILE TOE REGION

摘要

End bearing load transfer characteristics of bored precast piles equipped with expanded fabric bulb in toe region is investigated based on the use of hyperbolic transfer function for shaft resistance as well as for toe resistance of the enlarged bulb portion. Based on the static loading test results, a piling method specific approach to estimate the transfer function parameters from correlation with average N-values is proposed and its reliability investigated. The reliability investigations include the vertical load resistance aspects as well as the confidence limits for vertical movement. It is confirmed that the shaft resistance of the enlarged fabric bulb portion is much larger compared to the conventional bored precast piles and the increase is a function of the pressure applied in injecting the cement slurry into the fabric sack to form the bulb On the average, it appears that the increase in bulb shaft resistance is of the order of 7% for every 0.1 N/mm~2 increase in pressure.