Crosshole Sonic Logging (CSL) is the most accurate and reliable technique for assessing the integrity of deep foundation elements constructed on-site from concrete or grout. The crosshole sonic logging method is normally applied as a quality assurance (QA) technique for newly placed drilled shafts and auger cast piles, but can also be applied to slurry walls, mat foundations, and mass concrete pours.

CSL testing provides assurance that the foundation concrete is sound and contains no defects, such as soil intrusions, necking, sand lenses, voids, etc. The extent, nature, depth, and approximate lateral location of defects can be determined with the CSL method. The CSL method is typically performed in access tubes (steel or PVC) of 1.5 inch I.D. or greater which are tied to the rebar cage and cast into the shaft at the time of construction.

The test can also be performed using coreholes, if available. A variation of this method, called Single-Hole Sonic Logging (SSL) can also be used on smaller diameter drilled mini-piles and auger cast piles. The single hole sonic logging method is used in cases where only a single access tube can be placed in a shaft, and tests the concrete quality in the region around the single access tube.

In cases where a defect or other anomaly is located with the CSL method but more information is needed about the defect size, shape and nature, we can perform Crosshole Tomography (CT) testing. The Crosshole Tomography method is used to create a 2D or 3D image of the interior of the foundation element in the area of the defect to determine defect size, shape, and location.