Load tests on drilled shaft foundations in moderately strong to strong limestone

Abstract

Three drilled shaft foundations (DSFs) were constructed in moderately strong to strong limestone at the Siloam Springs Arkansas Test Site (SSATS). The embedment lengths within the limestone were 3?0, 1?5 and 2?1 m for the DSFs with diameters of 1?2, 1?8 and 1?2 m, respectively. The DSFs were instrumented to facilitate cross-hole sonic logging testing and full scale load testing using bidirectional load cells (BLCs). Lessons learned from construction included the: (1) proper concrete pouring techniques; (2) ability to retrofit improperly installed telltale instrumentation; and (3) influence of rock socket length within moderately strong to strong limestone. Recommended design, construction and testing techniques in moderately strong to strong limestone are presented. Based on the full scale testing, t-z model recommendations for weathered limestone and moderately strong to strong limestone are presented and discussed. Comparisons between measured unit side resistance and current design recommendations are also considered.