Large tonnage tests on super-long piles in soft soil area

A 2800-t static load test on super-long bored piles is conducted for a building 350 m in height in Wenzhou, which indicates that the heaped load supported by piles and beam-reaction system can be chosen to complete the large tonnage static load test in soft soil area. About 25% of the load at pile head is shared by the axial force at pile end, and the super-long piles work as end-bearing friction piles under the maximum loading. The percentage of super-long pile top settlement caused by the compression of pile shaft is over 90% under the working load. Therefore, the influence of pile quality on the settlement of pile top must be fully taken into account in design. In addition, the settlement of super-long piles is closely associated with the compressibility of the sediment at pile end. The shaft resistance of piles has a slight weakened and enhanced effect in the upper and lower soils, respectively, which means that the shaft resistance in different soil layers and the tip resistance should multiply different modification coefficients in estimating the bearing capacity of super-long piles. The ultimate pile-soil relative displacements for completely mobilizing the shaft resistance are found to be about 5 to 7, 6 to 8 and 8 to 10 mm in silt, silt clay and silt mixed with silty sand, respectively.