Crosshole Sonic Logging (CSL) verifies the integrity of drilled shafts. Single Hole Sonic Logging (SSL) is a similar test performed in foundations of smaller diameter, such as augered cast-in-place piles.

Drilled shafts are prepared for integrity testing by CSL during their construction, by installation of at least three tubes of 2 inch (5.08 cm) inside diameter. These tubes are usually attached to the reinforcement cage along the full length of the shafts. After concrete has been poured, the tubes are filled with water. A single PVC tube is installed for SSL.

GRL engineers perform cross hole sonic logging and single-hole sonic logging with the Cross-Hole Analyzer (CHA) by Pile Dynamics.

In CSL, a transmitter emits an ultrasonic signal in one tube and the signal is sensed some time later by the receiver in another tube. Poor concrete between the tubes will delay or disrupt the signal. The GRL engineer starts at the bottom of the shaft and moves the transmitter and receiver upward, until the entire shaft length is scanned. The engineer repeats the test for each pair of tubes. In SSL, transmitter and receiver are inserted in the same tube, and the procedure is similar.

The GRL engineer interprets data in the field and later reprocesses it in the office, furnishing a detailed and illustrated report. Tomography analysis is often performed during reprocessing.

GRL performs this foundation integrity test in accordance with ASTM D6760-08 - Standard Test Method for Integrity Testing of Concrete Deep Foundations by Ultrasonic Crosshole Testing