Defects in Drilled Shaft Foundations: Identification, Imaging, and Characterization

Federal Highway Administration2005PDFTech ReportJalinoos, FrankMekic, NatasaGrimm, Robert E.Hanna, KanaanUnited States. Federal Highway Administration. Central Federal Lands Highway DivisionHaramy, Khamis Y.Anderson, ScottSurdahl, R.United States. Federal Highway Administration. Central Federal Lands Highway DivisionUnited StatesConcreteStrength of materialsLogging (Recording)Foundation engineeringTestingNondestructive testsTemperature measurementTomographyConcrete StrengthCrosshole Sonic Logging (CSL)DefectsDrilled Shaft FoundationsEngineering Properties of ConcreteIntegrity TestingGamma- Gamma Density LoggingMaturityNondestructive Testing (NDT)Temperature MonitoringTomographyFHWA-CFL/TD-05-003DTFH68-03-P-00116Haramy, KhamisCOTR: Khamis Haramy, FHWA-CFLHD. Advisory Panel: Scott Anderson, FHWA-FLH and Roger Surdahl FHWACFLHD. This project was funded under the Federal Lands Highway Technology Deployment Initiatives and Partnership Program (TDIPP.)This report addresses two key issues needed by the foundation engineer to assess the structural integrity of drilled shaft, or other concrete structures that contain access tubes; specifically: a) What constitutes a defect in a drilled shaft?; and, b) How to relate observed defect in a velocity tomogram to engineering strength information? This study was conducted based on the development of a three-step approach: 1) Anomaly Identification and Independent Verification - This step allows the engineer to identify and independently verify suspected \u201canomalies\u201d in drilled shafts. It is concluded that both crosshole sonic logging (CSL) and gamma-gamma density logging (GDL) must be used. For velocity imaging of the shaft\u2019s interior, three-dimensional crosshole sonic logging tomography (CSLT) is required. 2) Defect Definition \u2013 A statistical approach is presented to define a cut-off velocity to separate CSLT velocity distribution of sound concrete from the velocity distribution of anomalous concrete. The cut-off velocity is then used to volumetrically image a \u201cdefect\u201d volume. 3) Defect Characterization \u2013 Finally, changes in velocity values in the defect volume is correlated to changes in concrete strength and a 3-D strength image is developed for integrity assessment by the engineer. The velocity-strength correlation is developed in the laboratory using cylinders with the same design mix as the shaft and allowing for maturity. Therefore, this study proposes a complete analysis and technical information to assist the foundation engineer and owner agencies in deciding to accept, remediate, or reject a given shaft or a wall structure.96