Uncertainty in pile resistance from static load tests database

This paper tabulates the results of 175 static load tests carried out in Ireland, and includes bored, continuous flight auger and driven piles in fine- and coarse-grained material, and also piles terminating in rock. These data are used to show that the ultimate pile resistance (defined at 0·1 times the effective pile diameter, D) predicted using Chin's extrapolation method was within the range 85–100% of the measured resistance when the pile head settlement was greater than 0·05D. The coefficient of variation of the compressive resistance of the ground against a pile, R_c, for a varying number of load tests carried out on a site reduced from 40% where a single test was carried out to 20% where eight tests occurred. This is considered to be a reasonable lower bound to the within-site variation in R_c, and it is recommended that this level of variation be considered for pile design.