Optimization of Drilled Shaft Design Using High Strain Dynamic Monitoring

Abstract

High capacity of rock-socketed or end bearing drilled shafts is often not fully exploited due to the highly conservative design that many local codes and local practices around United States dictate. This reduces the cost efficiency of drilled shafts versus other foundation solutions. ADSC is interested in developing a test program procedure that will be economically feasible for engineers and foundation contractors to perform in every project even when load tests are not specified. Static load tests (including conventional top-down and bi-directional load tests) are invaluable but often prohibitive due to high cost and time constraints. Alternatively, high strain dynamic testing of drilled shafts has increased significantly in recent years with well-established testing procedures and analyses. More specifically, ADSC is considering using dynamic load testing to prove the high capacities of drilled shafts in several rock formations around the country and establish limits of extrapolation to larger diameter shafts from tests on smaller diameter shafts. The purpose of this paper is to present the theoretical basis of ADSC’s technical endeavor. More specifically the paper will focus into 2 different topics; i) parameters affecting drilled shaft performance and ii) the theory and principals of dynamic testing as applied to rock socketed drilled shafts, as well as, case studies of dynamic tests in rock socketed drilled shafts.