Proceedings - 13th International Workshop on Micropiles - 2017, Vancouver, BC, Canada, (ISM, DFI, ADSC)
MICROPILE QA/QC TESTING USING THERMAL PROFILING
William B. Wright, P.E., Matthew, L. Silveston, P.E., Thomas C. Smoak, III, P.E., William L. Snow, Jr., P.E.
With increasing frequency, hollow bar micropiles are being used as a foundation solution along Coastal South Carolina. On a recent project, micropiles were installed using a size 40/20 and 52/26 continuously threaded, hollow core steel bars. The hollow space in the bar allowed an innovative application of Thermal Integrity Profiling (TIP) equipment, normally used for drilled shaft installation verification, to be applied to micropiles. We utilized a single strand of thermal wire sensors inserted into the hollow center bar after completion of micropile installation. A data logger recorded the concrete temperature over a 24 to 36 hour period as heat was generated during the exothermic hydration reaction. Processing software then used the temperatures recorded to generate a 3-dimensional model of the micropile. The adopted building code in South Carolina is the 2015 IBC, which requires full time inspection of cast-in-place foundations and requires verification of element diameters. Using the known pile length and grout volume, the average pile diameter can be calculated. However, none of the required inspection methods allows direct verification of the pile diameter, which may vary with depth and soil strata. TIP testing can also detect micropile defects including cave-in or clogged soil cuttings which prevent full grout cover and protection of the steel center bar from corrosion. Even load tests, which are the ultimate proof of capacity, cannot guarantee that defects are not present. While load tests are generally performed on 1% to 2% of the production piles, the ease of TIP testing allows for inspection coverage of 10% to 20%. While this method of verification cannot replace full time inspection of a qualified inspector or load testing, it can be performed relatively easily, and is another valuable and innovative method to determine proper pile installation.
|article #2644; publication #1033 (ISM- 2017)|