Thermal Integrity Profiling (T.I.P.) Limitations

by FTC
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Due to heavy promotion by the manufacturer and other parties T.I.P. testing requirements are growing for drilled shaft projects throughout the United States. T.I.P. involves collecting temperature data generated by the heat of hydration from the curing cement in the drilled shaft concrete in attempt to identify potential anomalies in the drilled shaft installation. Such data collection is performed by using embedded wires or by using probes within temporarily dewatered CSL access tubes typically within 12 to 72 hours following concrete placement (time window depends primarily upon the shaft diameter).

FTC has performed T.I.P. testing for numerous drilled shafts using both wire and probe data collection methods throughout the United States. Based upon our extensive experience (and considering we are not involved with manufacturing or sale of T.I.P. testing equipment) we would like to offer the following independent opinions about this test method.

T.I.P. is a far less accurate method compared to the well-established cross-hole sonic logging for drilled shaft integrity testing. As such, T.I.P. testing should only be used to supplement CSL testing. In no case should T.I.P. be the sole method of non-destructive drilled shaft testing performed for a given drilled shaft. This is because the T.I.P. test is based upon not only how a drilled shaft heats from the curing cement by also how that heat is retained or dissipated along the top and bottom boundaries of the shaft and along the length of the shaft.

FTC has performed thousands of CSL tests for drilled shafts throughout the United States and Canada. Based upon our extensive experience we have observed that the majority of drilled shaft anomalies occur at the very bottom (which account for the vast majority of shaft anomalies) or very top of the drilled shaft. Unfortunately given the inherent temperature differences at these boundary locations it is virtually impossible to adequately resolve the T.I.P. analysis results to within a few feet of the top and bottom of the shaft. Such zones are often critical to the design performance of the shaft. Without the benefit of subsequent CSL testing which permits data collection within a few inches of the top and bottom of shaft, the owner might require concrete coring to verify the integrity of critical shaft installations.

A benefit of T.I.P. testing would be to perform testing 1 or 2 days prior to performing CSL testing for a given shaft to determine whether a major problem (such as loss of tremie seal) had occurred during concrete placement. Such T.I.P. information could be used by the contractor to adjust means and methods prior to the concrete placement for the next shaft before CSL testing would be performed on the previous shaft to confirm the anomaly.

Other concerns that we have about the way T.I.P. testing is being promoted involves the assertion that problems with cage alignment or concrete cover thickness can be accurately determined. We have seen many instances where the T.I.P. results indicated negative concrete cover (computed edge of concrete was inside the main reinforcing cage) on shafts with a permanent casing surrounded by cold lake water. Clearly this result was not accurate and was caused by overall ambient temperatures of 100 degrees F in the shaft, 40 degrees F in the lake and 58 degrees F in the soil and rock. Also, there are localized temperature variations caused by differing thermal conductivity values between changes in soil and rock strata that have nothing to do with development of the heat of hydration within the drilled shaft concrete. At any rate, if the result of a T.I.P. test indicates a potential concern with concrete cover thickness or reinforcing cage alignment how would such concerns be verified using other test methods? 

In summary we fully support the development of new testing methods for drilled shafts but adoption of new technologies should only be made with the full understanding of the benefits and limitations of such methods and they should not replace more established and accurate test methods.