Skin Friction of Large Diameter Piles Socketed into Rock.

The results of five axial loading tests on large-diameter drilled piles socketed into rock are discussed in this paper. The piles were built on an Italian site where several shallow rock formations are found below loose soils. Pile sockets involved rocks with different strengths such as: marl, limestone, gypsum and diabase. The pile response during static loading depended on rock strength, length of the socket in rock, and length of the pile in soil. In this paper, an analytical model is used to evaluate the limit skin friction at the pile-rock interface. The model is based on the hyperbolic transfer function technique and allows back-analyses to be carried out easily. Following current empirical approaches, a preliminary appraisal of the model parameters is made using extensive data from laboratory and in situ tests. The parameters are subsequently modified by fitting the measured pile head displacements to computer simulation results. The shaft resistance values obtained from the analyses are compared with published values and found to be lower.