Thermal Integrity Profiling (TIP) and Crosshole Sonic Logging (CSL) Testing For Drilled Shafts
Advisor: Professor Timothy D. Stark
Thermal integrity profile (TIP) and crosshole sonic logging (CSL) tests were performed on three test drilled shafts at three different locations in Illinois with pre-planned flaws installed to determine which technology is effective at identifying installed flaws. Using preliminary analysis methods, TIP testing was found to be more effective than CSL in identifying installed flaws outside the rebar cage. Conversely, CSL was found to be better than TIP at identifying installed flaws at the bottom or toe of the drilled shaft. TIP results at one-half the time to peak temperature were found to provide better identification of flaws than at the time to peak temperature. However, this study also shows that TIP results could provide the best identification of flaws at the end of the acceleration stage (stage 3) of concrete hydration, which has the highest rate of temperature increase with time and happens to be at one-quarter of the time to peak temperature. Concrete coring near the rebar cage was shown to provide better identification of the flaws than coring at the center of the drilled shaft because the flaws tend to be pushed toward the perimeter of the drilled shaft during concrete pouring. The findings of this study were used to create a decision flowchart that can be used to assist practicing engineers in the selection of the most appropriate nondestructive testing for drilled shafts in Illinois. In addition, modifications to the existing TIP and CSL specifications were proposed. Level 2 analysis was also performed on all three test drilled shafts using superimposed construction logs and concrete yield data with hyperbolic correction for shaft ends. It was found in this study that current TIP testing interpretation methods don’t provide a reference temperature to be compared with those measured from TIP testing. Therefore, a numerical model was constructed using COMSOL Multiphysics® software package to numerically model concrete heat of hydration for these three drilled shafts during curing. The 3D numerical results were validated and matched the temperatures at one-half the time and full time to the peak temperature measured by the TIP wires for all three drilled shafts. Additionally, measured temperatures with time at different depths in all drilled shafts also match the modeled temperatures with time profiles. The pre-planned flaws installed in the three test drilled shafts, which consist of soil inclusions and tremie pipe raises, were successfully modeled in this study and are reflected in the measured TIP temperature data. Concrete heat of hydration of drilled shafts was found to be insensitive to soil type and their initial temperature. The concept of mass concrete is discussed in this chapter as well in terms of maximum temperature at the center of large drilled shafts and the difference between the temperature at the center and near the soil concrete interface based on the guidelines from ACI and IDOT. It was shown that the initial concrete temperature has the largest influence on the peak temperature at the center of the drilled shaft and on the maximum temperature difference. The validated 3D numerical model developed herein was used to create a user-friendly application to assess practicing engineers in the interpretation of TIP data for future drilled shafts. This application provides a reference temperature for measured TIP data to be compared with the measured temperature along with the measured bottom roll-off temperature profiles.