Defect Analysis for CSL Testing

Cross-hole Sonic Logging (CSL) has become a common method to evaluate the integrity of drilled shafts. However, the interpretation of test measurements by this method requires some judgment and experience. Many previous proposals rely solely on the arrival time, or wave speed. A proposed method which takes into account both arrival time and signal strength is presented. If defects are detected, then in some cases a tomography analysis may be helpful to further quantify the result. The situations where tomography is useful will be discussed. Recommendations are given for the type and amount of data required for a tomography analysis. This discussion is illustrated with a case history of a test shaft with purpose built defects to demonstrate the advantages of these evaluation methods.