Bored precast piles equipped with grouted bulb in the toe region

Vertical load bearing resistance of the expanded fabric bulb embedded in the bearing stratum and located in the toe region of a bored precast pile is investigated based on the loading test results. Loading test results are utilized to propose the piling method specific approach to estimate the vertical resistance from correlation with average N-values and its reliability investigated. The reliability investigations include the vertical load resistance aspects as well as the confidence limits for vertical movement. It is seen that the shaft resistance of the enlarged fabric bulb portion is much larger compared to conventional bored precast piles. The increase is most likely due to the additional lateral restraint developed when seamless fabric sack is pressure grouted to form the bulb. The toe resistance of the fabric bulb, however, is comparable to what may be expected in other bored precast piling methods.