Effects of residual stresses on shaft friction of bored cast in situ piles in sand

The existence of residual stresses locked-in prefabricated displacement piles is a well-known problem and has been addressed by a number of researchers in the last decades. This is not the case with cast in situ piles: as a consequence of concrete curing, pile-soil interaction starts soon after concrete casting, causing stress changes in terms of both normal and shear stresses. Such circumstance has been confirmed by few experimental evidences, reported in the paper, in saturated or dry soil conditions. In order to evaluate the influence of residual stresses on the subsequent pile response to axial loading, a broad parametric study has been carried out by means of numerical modelling. Particular focus is given to the effects induced on the shaft friction of floating bored piles embedded in wet and dry sandy soils. The results have been interpreted with the aim of highlighting errors commonly made if a stress-free pile is assumed when interpreting a specific load test results on instrumented piles and/or arranging general design methods.