the technology has been validated by the more than one million readings from digital temperature sensors, which have been used on hundreds of successful installations across the world. The results from the sensors, along with a great deal of practical experience, provide a sound basis for responding to the questions most asked. What you don’t see can hurt you. Various studies have determined that between 20% and 38% of shafts contain some level of anomalies Installation And Measurement TIP uses the heat generated by the curing cement (i.e., hydration energy) to assess the integrity or quality of the cast-in-place concrete foundations (e.g., drilled shafts, micropiles, augered cast-in-place piles and drilled displacement piles, collectively referred to herein as “shafts”). The expected temperature at any location is dependent on the shaft diameter, mix design, time of measurement and distance to the center of the shaft. TIP measurements can be used to estimate the actual shape of the shaft. These estimates can be compared with the concreting logs to assess the overall quality of the shaft. Because the method relies on the heat of hydration, TIP testing is generally done between 8 and 48 hours of concrete placement. The optimum TIP testing time is dependent on the shaft size and concrete mix, and could range from 4 to 72 hours. Sma l l e r s h a f t s a r e typically tested earlier in the range of testing times. Data is acquired via the thermal wire cables, which are tied to the steel reinforcement (rebar cage or center bars) along the vertical alignment of the shaft prior to the installation of the reinforcement and prior to concreting. TIP measurements indicating tempera- tures that are cooler than normal indicate inclusions, necking or poor quality concrete. Whereas, measurements indicating tem- peratures warmer than normal are indicative of bulges outside of the cage diameter. Variations in temperature between diagon- ally opposite pairs of thermal wire cables reveal cage eccentricities (i.e., cage misalignment). Acceptance Criteria The acceptance criteria described below provides engineers a powerful tool to ascertain quickly which shafts are acceptable and which may need further analysis and/or remedial measures (e.g., coring). The load carrying capabilities of shafts may be controlled by the geo- technical side shear resistance or structural bending and/or compression, which are directly related to the diameter or circumferential surface area, moment of inertia and cross sectional area, respectively. Although the use of the TIP Wire Cable System is increas- ing in acceptance with many Departments of Transportation, the technology is relatively young and many geotechnical and structural engineers are still unfamiliar with it. The reduction in radius and reduction in capacity is related in a linear, square and fourth power manner for side shear, compression and bending, respectively, as shown in the figure at top of following page. The reduction or loss of section is assumed to occur in the worst case position, which would be on the outside of the reinforcing cage. While the average radius or diameter provides an indication of the cross-sectional properties, the local radius or diameter is a better indication of the concrete cover and cage alignment or eccentricity. For highway bridge substructures, the AASHTO recommended minimum cover of 4 in (100 mm) is used in many shaft designs across the U.S., but some states may have different acceptance criteria based on their local needs or conditions. If the criteria for the reduction of radius Thermal readings from 10 individual sensor arrays, which reveal anomaly at same depth shown in core 90 • DEEP FOUNDATIONS • MAR/APR 2017 was 0% to 6% and >6% is applied to shafts as “satisfactory” and “anomaly” (requiring further evaluation), respectively, the computed net effect on the shaft properties are summarized in the table.
