Study of time effect on vertical bearing capacity of open-ended pipe pile

Time effect is defined as an increase in pile capacity over time after installation. The statistical analysis reveals that the average increase rate of bearing capacity for single pile is in the range of 15%-29% per log cycle. The set-up on the pile capacity is mainly due to the consolidations, the gains on shear strength, the aging, the creep and shell effect of surrounding soils. Based on the mechanism of pile set-up, a three-phase conceptual model is establisbed. In addition, a computation model is proposed based on consolidation theory for evaluating the soil set-up on pile capacity. The research indicates that the relative setup rate for friction-type open-ended pile under full coring condition is 10% larger than that for corresponding closed-ended pile.