Interpreting CAPWAP results for driven piles with corrections for setup and residual loads

Abstract

Evaluation of pile capacity using dynamic testing and Case Pile Wave Analysis Program (CAPWAP) analysis has been shown to provide reasonable measurements of capacity and separates the shaft and tip resistance. It is a common method for verifying pile capacities; however, consideration of setup and presence of residual loads at the time of testing are necessary for interpreting the resistance distribution. A test pile program was conducted that included dynamic testing of piles at the end of initial driving and early restrikes to measure the rate of setup. The piles were instrumented to measure residual stresses. The shaft resistance and tip stiffness were interpreted from analyzing multiple blows and corrected for residual stresses. The results from CAPWAP were compared to measurements from static load tests. It was found that correcting CAPWAP results for residual loads resulted in better interpretation of the rate of setup and resistance distribution. Analyzing successive blows with CAPWAP provided an improved estimate of the tip load–movement curve by extrapolating the increase in tip capacity with penetration. The results demonstrate the importance of correcting CAPWAP results for residual stresses to gain a better understanding of the pile capacity, resistance distribution, and tip stiffness for design purposes.