The paper was produced by a CSL Task Force comprised of members of the DFI Codes and Standards Committee, Drilled Shaft Committee and Testing and Evaluation Committee. The CSL Task Force was chaired by E. Anna Sellountou of Pile Dynamics.

The white paper reviews the state of the practice (including experience gained over the past 20 years), proposes improved CSL rating criteria and makes recommendations for additional assessment, as well as educate the industry on the proper interpretation of CSL testing.

Non-destructive testing of drilled shaft foundations via crosshole sonic logging (CSL) is often performed as part of the quality assurance process to assess the soundness of concrete. The intent of CSL testing is to identify irregularities such as soil intrusion, necking, soft bottom, segregation, voids and other defects that could result in poor structural performance of the foundation. Over time, CSL rating criteria based on first arrival time and relative energy have incorrectly evolved to often be the sole means of determining the acceptability of a shaft. Some of these criteria have found their way into regulatory agency specifications, with acceptance values often differing from agency to agency.

The 17-page paper is available as a free download.