The construction of the drilled shaft foundations began in July 1992. By the end of January 1993, all three shafts were instrumented. The concrete frame of superstructure was completed by the end of November 1993. The load and displacement variation of the shafts were monitored from the time concrete was poured, and the changes in tip load and side friction recorded for nearly two years.
All measurements are with respect to the day the shaft concrete was poured, designated as day one.
Tip load variations in first 28 days after shaft concrete was poured In typical drilled shaft load tests, the shafts are usually allowed to gain 28 day compressive strength before the loading is applied. In this project, the measurements were taken before and during the placement of concrete, and will continue over the service life of the structure. This will permit the investigation of the early performance of the shaft, and demonstrate the actual load transfer mechanisms. The slow increase in the shaft loads was measured as the structure was built. From Figure 4 it is observed that within one day after the concrete was poured, the tip pressure reached a peak value, which is very close to that corresponding to the total concrete weight.