Static and Dynamic Load Test Comparison for H-Piles in Missouri River Alluvium: Fid-Bau Portal

Static and Dynamic Load Test Comparison for H-Piles in Missouri River Alluvium

Axtell, Paul J. / Boeckmann, Andrew Z.

High-strain dynamic pile testing (HSDT) is a useful tool, particularly when used in combination with subsequent signal matching (SM) and restrikes. Primary benefits include (1) determination of actual driving energy, (2) an approximate assessment of the in situ integrity of the pile, and (3) an estimate of the static resistance of the pile. Limitations do exist, particularly with respect to benefit (3), that are not well publicized, and the limitations are not commonly appreciated among consumers of HSDT reports. This paper compares the results of five top-down static compressive load tests (SLT) with HSDT and SM results of the same piles to provide a quantitative example of the limitations of HSDT/SM. Static load test results from all five test piles exceed HSDT/SM results from beginning of restrike (BOR). The restrike HSDT/SM underestimated the SLT results in all cases between 21% and 31%, with an average underestimation of 25%. Details are provided to inform the industry of at least one set of circumstances where HSDT/SM do not provide accurate estimates of the static resistance of piles. While it is understood and well documented in most design codes that use of SLT produces a greater degree of confidence (and, in turn, a greater resistance factor) than HSDT/SM, the results of this project indicate the lower confidence can be compounded by underestimations of resistance, possibly leading to overly conservative designs.