Cross-Hole Sonic Logging (CSL) — Sonic Test This is a high accuracy ultrasonic test, usually for bored piles with tubes. How it is done 1. Install CSL tubes inside pile cage before concreting. 2. After concrete sets, fill the tubes with water. 3. Lower transmitter in one tube and receiver in another. 4. Ultrasonic waves travel through the concrete between the tubes. 5. Device measures how fast or slow the wave passes. What CSL tells you • Very accurate detection of honeycombing • Weak concrete z