Crosshole Sonic Logging (CSL) Testing per ASTM D-6760 Standard Test Method for Integrity Testing of Concrete Deep Foundations by Ultrasonic Crosshole Testing, is the most accurate and reliable technique for accessing the integrity of deep foundation elements constructed on-site from concrete or grout. FTG is a leader in CSL testing, performing over 1,000 CSL tests per year in a wide variety of states such as Maryland, Virginia, New York, New Jersey, Pennsylvania, West Virginia, North Carolina, South Carolina, Arkansas, Oklahoma, etc.
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 with no defects such as soil intrusions, necking, sand lenses, voids, etc. The extent, nature, depth, and approximate lateral location of a defect(s) can be determined with the CSL method. The CSL method is typically performed in access tubes (steel or PVC) of 2-inch I.D. which are tied to the rebar cage and cast into the shaft at the time of construction. The test can also be performed using core holes (if available). The method sends a sound wave between the source and receiver tubes to determine the wave speed of the matrix. This wave speed plot is then analyzed to determine if low velocity voids, defects or anomalies are encountered. CSL testing has high repeatability and testing can be re-performed at later dates to determine improvements from additional concrete curing. In case deficiencies are determined, Crosshole Tomography can be used.
Crosshole Tomography analyses can be done to better characterize the shape of an anomaly identified in Crosshole Sonic Logging between a tested tube pair. We use the Windows-based TOMO-1 software and Slicer/Dicer software for users of an Olson Instruments Crosshole Sonic Logging system. The software is used to image a defect in a foundation using ultrasonic velocity Crosshole Tomography.
Data acquisition involves performing typically 50 to 60 CSL logs in which each log has a fixed hydrophone receiver depth and the source is pulled from below to above the potential defect zone. The hydrophone is positioned below the defect and then raised in equal increments of about 3-6 inches (7.5-15 cm) until it is above the defect. Zones of tomography are typically 5 to 8 feet in thickness. Extensive data is acquired by testing all the angles between a tube pair. The tomographic analysis is then performed on picked travel times to delineate areas of slower velocity, poorer quality concrete.
The ability given by Crosshole Tomography testing and analysis is the ability to see the shape of an anomaly to better judge its extent and severity between each tested tube pair. This allows engineers and contractors to determine if repairs are needed, and where the repairs need to be performed. If enough tube pairs are tested, one can also obtain a 3-D image of the shape and extent of the anomalies.
Low Strain Integrity Testing (PIT) performed per ASTM D5882, also uses soundwaves to determine the pile or shaft integrity from the ground surface in the absence of CSL tubes or post remediation.
During the CSL or PIT test analysis and reporting phase, FTG leads from the front, rather than just noting the presence of an anomaly or defect, we seek to determine how it occurred, how to prevent its reoccurrence and how to solve the foundation issues caused by its creation. FTG’s Chief Engineer has performed Crosshole Sonic Logging since 1996. Mr. Jeff Goodwin, P.E. is a recognized expert in the field and has made numerous presentations on CSL testing, foundation NDE and drilled shaft remediation for the ADSC, DFI & ASCE.