Axial load tests on drilled shafts socketed in hard clays and shales

An investigation into the load-settlement behavior of two drilled shafts, founded in shale, is presented. The motivation for this research is to advance the understanding on how drilled shafts react under loading in stiff clays and shales. The objective of this study is to improve the understanding of axial capacities for rock-socketed shafts in hard clays and shales. In order to achieve this objective, the research team measured the strengths within the subsurface material at the test site, estimated the unit side shear and unit end bearing of the shale-shaft interaction by running two axial load tests using the patented Osterberg-Cell™ (O-Cell) loading technique, and compared the results to the current design methods that are used to predict the axial capacity of drilled shafts. The results of the study concluded that the current methods for estimating unit end bearing developed by the Texas Department of Transportation (TxDOT) and the Federal Highway Administration (FHWA) provide fairly accurate predictions when compared to the measured information However, it was discovered that the measured ultimate side resistance steadily decreased nearing the tip of the shaft. A limited amount of information is currently available for load tests performed in soils with Texas Cone Penetration (TCP) values harder than 2-in per 100 blows. The results presented herein demonstrate the effectiveness of the current design methods for drilled shafts and the non-uniformity of side resistance within one- to two-diameters