Comparison of Non-Destructive Integrity Tests on Experimental Drilled Shafts

"An experimental program focusing on four drilled shafts was conducted to determine the effect of high strength steel reinforcement bars on lateral resistance, steel casing on axial and lateral resistance, and steel casing without internal reinforcement on lateral resistance. Thermal Integrity Profiling (TIP) Thermal Wires and crosshole sonic logging (CSL) access tubes were installed in each shaft, and thereafter the corresponding non-destructive testing (NDT) was performed on each shaft to assess the integrity of the shafts and to compare the results from the different NDT methods. The results of the CSL tests using scored PVC tubes are compared against those conducted in 73/56 fully-threaded steel hollow bars, whereby the results indicated that the threaded bars served as a good host for performing the CSL tests. The data from the TIP Thermal Wires is compared against the results from the CSL tests for each of the four shafts, and the similarities and discrepancies between the two methods are discussed. This paper will serve as a reference to those interpreting the measurements and data obtained by performing nondestructive integrity tests on drilled foundations.INTRODUCTIONNon-destructive tests (NDTs) embody a set of critical tools for the evaluation of the integrity of constructed deep foundations, particularly for cast-in-place foundation elements. Construction defects may require the rejection of the foundation element by the owner’s representative, resulting in costly repairs or replacements and delays to the project schedule. The use and appropriate interpretation of the results from the NDTs provide the information required when evaluating the integrity of these constructed elements. A cooperative research program was conducted to assess the effects of various construction variables on the axial and lateral performance of drilled shaft foundations, which provided an opportunity to compare the established Crosshole Sonic Logging (CSL) test method to the newer Thermal Integrity Profiling (TIP) Thermal Wire method. This paper presents an overview of the experimental program performed at the geotechnical test site at Oregon State University (OSU), details of the CSL and TIP installation and testing methods, and the results of the NDTs on the constructed drilled shafts. Because one of the shafts was constructed with fully-threaded longitudinal steel hollow bars, this experimental program also allowed the assessment of the use of the hollow bars as access tubes for the CSL tests. Both the CSL and TIP test methods indicated that the shafts were of good quality and free from defects or anomalies; the data obtained using the TIP method also provided an estimate of the as-constructed shaft diameter and the reinforcement cage alignment, which will prove helpful when back-calculating axial and lateral load transfer during future loading tests."