Discussion Of The Prestressed Pipe Pile Ultimate Bearing Capacity

The key to pile design is to determine the bearing capacity of vertical piles. However, no method in China can give accurate determination of the vertical bearing capacityof prestressed piles at present, except a few international empirical formulas. If we determine the bearing capacity with the existing standard of empirical formula, more often than not the trial value will be less than that from the static load test. Starting from the squeezing effect on soil of prestressed piles, this paper has analyzed the mechanical load-bearing characteristics and the loading mechanism of prestressed piles, explained that the existence of squeezing effect on soil and the low parameter of physical capacity of the bearing stratum of soil are the main reasons for the increase of practical vertical bearing capacity of prestressed piles. Based on the theoretical analysis, this paper has made Statistical induction of the static loading test data from 11 projects in Tianjin and Chengdu, and analyzed the differences between practical bearing Capacity and designed bearing capacity; found some rules about the effect on vertical bearing capacity of prestressed piles from squeezing effect soil, diameter and length of the pile, the characteristics and compacting degree of the bearing stratum of soil; verified that the present standard value of the ultimate tip resistance of gravel layer in geological survey in Chengdu is too conservative; made some amendments to the standard value of ultimate tip resistance when the bearing stratum under the precast piles is gravel layer provided in Construction Pile Foundation Technology Standard; and by comparing calculated and measured values, verified the applicability of the amended standard value of the ultimate tip resistanceto the pile.