Crosshole sonic logging (CSL) is a method to determine the structural integrity of drilled shafts and other concrete piles.
The CSL method is considered to be more accurate than sonic echo testing in the determination of structural soundness of concrete within the drilled shaft inside of the rebar cage.
Also known as Crosshole Acoustical Testing, CSL normally requires steel (preferred) or PVC access tubes installed in the drilled shaft and tied to the rebar cage.
Areas of signal loss or wave speed reduction greater than 10 percent represent potential physical anomalies and can be targeted for further exploration.
A more advanced, higher-end analysis that creates a mock 3-dimensional graphical display of the concrete soundness throughout the pile is known as Crosshole Sonic Tomography.