A Modified Case Method for Piles with Section Step Changes

Applied during pile driving, the Case Method offers an immediate estimate of the static resistance to driving (SRD) after each hammer blow. It has been used in its original form both in the onshore and offshore piling industry for more than 40 years to provide an indication of the pile static capacity. The Case Method requires measurements of force and velocity near the pile head as the hammer strikes the pile and produces an analytical estimate of the SRD, using a number of assumptions. One of them requires the pile to be of constant impedance (or cross section) along its length. However, for reason of economy, driven piles are often composed of several sections of different cross sections. The Case Method provides in that case an inaccurate estimate of the SRD. This article presents an improved version of the original Case Method which takes into account possible variations of impedance along the pile. A numerical validation shows that for piles displaying impedance changes, the modified Case Method presented herein provides an estimate closer to the actual SRD than the original Case Method. That conclusion is further validated by applying the modified Method to pile driving records and comparing its results to SRD estimates obtained through more reliable modelling.