Static and Dynamic Models for CAPWAP Signal Matching

Signal matching is the preferred analysis method for Dynamic Load Test (DLT) evaluations. It is applicable to DLT records of driven piles, auger-cast piles, drilled shafts, and even on dynamic penetrometers. Although signal matching is considered standard best-practice, required by many code specifications and therefore routinely used on thousands of deep foundation projects worldwide, and of significant importance to the deep foundation industry, many features of the CAPWAP® signal matching model and procedure are not well known. CAPWAP's signal matching is possible because of the availability of redundant measurements of load and movement, and it is necessary to determine the unknown boundary conditions. The goal of CAPWAP is the determination of dynamic and static soil resistance parameters of the generally accepted Smith-type pile-soil interface model. However, the classic Smith model cannot explain some of the phenomena that occur during the impact event. For reliable signal matching results, therefore, several modifications of the original Smith model were made. While some modifications fundamentally do not affect the signal match, other more substantial changes are of considerable importance to the reliable determination of the all-important static load bearing capacity result. Before discussing the CAPWAP procedure and its automatic analysis tools, this paper describes the more unusual CAPWAP pile and soil model parameters and their effects on the final results. Measurement and analysis results from actual projects demonstrate the various features of the program and aspects of the models. The paper includes a summary of recommended limits for model parameters, match qualities, and calculation procedures and a few suggestions for additional research.