Knowledge Is Bliss-A Case for Supplemental Pile Testing to Ascertain Fidelity

Abstract

Full-scale static loading is a widely accepted test method for authoritative assessment of deep foundations. Testing is typically performed once and the result is considered the definitive answer regarding the pile's load bearing capacity. However, there are technical and operational reasons that may cause misleading results. This paper presents a case where a large concrete pile was subjected to two full-scale static, and several dynamic loading tests. The pile was initially driven to a predetermined depth based on conventional geotechnical analyses, and its capacity was confirmed by dynamic testing. However, the static loading test indicated a pile capacity well below the anticipated value. Dynamic testing performed during restrike one day following the static test indicated a capacity close to that of the static load test. The pile was subsequently driven 4.4 m deeper until dynamic testing indicated it had achieved the required capacity. A second static loading test was performed that confirmed the required capacity. A review of the construction records revealed that in preparation for the static load test, the reaction steel H-piles were vibrated to below the test pile toe following the installation of the test pile. Analysis of the dynamic and static testing results confirmed that the installation of the reaction piles adversely affected the bearing layer resulting in reduction of pile capacity and the failed original static test. Utilization of dynamic pile testing and geotechnical analysis made it possible to uncover the flaw in the static loading test setup procedure and, thus, the unreliability of the original static load test result. This case study demonstrates that static load tests can sometimes be misleading, and supplemental dynamic pile testing is a valuable tool to establish reliability and ascertain fidelity of results.