CAPWAP and Refined Wave Equation Analyses for Driveability Predictions and Capacity Assessment of Offshore Pile Installations

Abstract

Open ended pipe piles have to be driven in the offshore environment primarily as platform support piles or as conductor pipes. In either case, deep penetrations have to be achieved. In preparation of these potentially difficult installations, equipment selection and stress control is done by a predictive wave equation analysis. During pile driving, dynamic monitoring combined with CAPWAP signal matching analysis is a preferred method for bearing capacity assessment. After the fact, if dynamic measurements were not provided during pile driving, a wave equation analysis can again help perform a post-installation analysis for bearing capacity assessment, assuming a variety of parameters. Wave equation analyses require a variety of input parameters describing hammer and driving system performance and the pseudo-static and dynamic behavior of the soil. Measurements taken during the installation yield immediate results about hammer and pile performance. Soil resistance parameters can be extracted by careful signal matching analysis. Unfortunately, the measurement and associated analysis results cannot be used without further modification in the wave equation analysis, because the wave equation approach requires simplifications in hammer, driving system and soil models. Thus, a final step is the so-call Refined Wave Equation Analysis which combines all results obtained and produces a best possible match between measurements and analyses. This paper describes the process of the three analysis phases utilizing typical offshore pile installation records. The paper also gives guide lines for this analysis process as well as a summary of limitations. An important part of the paper includes recommendations for and discussion of the modeling of the soil resistance near the open ended pipe bottom. Finally, the paper discusses how the results should be used for greatest benefit of the deep foundation industry.