Crosshold Sonic Logging Goes Beyond Manual Inspections & Coring:
CSL can identify anomalies not identified through manual inspection or concrete coring. Crosshole Sonic Logging (CSL) is a nondestructive test method for evaluating the integrity of a variety of concrete structures such as drilled shaft foundations and slurry walls. The CSL method can provide a greater quantity of high-quality data as compared with previous evaluation test methods such as concrete coring. Currently, the largest application for CSL is the evaluation of concrete within drilled shaft foundations during construction
How is CSL performed?
Typically, 2-inch diameter, water filled, steel access tubes are installed in a shaft during construction. The number of access tubes installed is dictated by the size of the drilled shaft and rock socket, although 4 or 6 access tubes are typically installed in each shaft. A pair of transducers (one transmitter and one receiver) are lowered in a given pair of access tubes. For most survey applications, the transducers are located in a horizontal plane. The energy and arrival time for the sonic pulse, going from a transmitter to receiver, is recorded by the data acquisition system. The shaft is surveyed from the bottom to the top by simultaneously pulling the transducers through the access tubes. Typically, sonic data is recorded at intervals of 2-inches for the full length of the shaft. Often, a single shaft can be surveyed in an hour or less, and preliminary results are available while the test is performed in the field.
What does CSL reveal?
An engineer experienced in CSL data collection and analysis looks for any variations in the energy, arrival time and apparent sonic velocity within each data set. Such variations or anomalies can be indicative of zones of lower quality concrete, soil inclusions, or voids within the concrete. The CSL method can provide an accurate indication of the location and size of such anomalies. In some cases where an anomaly is detected, other test methods such as cross-hole tomography or concrete coring may be used to determine the viability of shaft repair or acceptance. The results of the CSL survey are then plotted and included with the report written by a registered engineer.
Why is CSL important?
By employing Crosshole Sonic Logging, it is possible to economically identify anomalies that would not be known through manual inspection methods or concrete coring. Often the information obtained in the CSL survey can be used by the contractor to modify construction methods and improve the quality of the drilled shafts.