Abstract: Permeable pipe piles are set in the soft soil foundation to accelerate the dissipation rate of excess pore water pressure induced by pile driving and then to accelerate the consolidation of soil around the pile. At present, there are many studies, including model tests and numerical simulation, on the bearing capacity and permeability performance of permeable pipe piles. However, few field tests have been conducted to deeply study the time effect of bearing capacity and load transfer law of permeable pipe piles. Based on the fiber Bragg grating (FBG) technology, the static load tests were carried out to study the strain distribution and internal force transfer of the permeable pipe pile in soft soil foundation. Meanwhile, the relationship between the variation of excess pore water pressure of the pile-soil interface with time at different positions of the pile body and the time effect of bearing capacity of the permeable pipe pile was analyzed. The test results showed that at the early stage of pile driving, the growth rate of bearing capacity of a single permeable pipe pile under increased vertical loads was higher, and then gradually decreased with time. Under the test site conditions, the improvement of the bearing capacity of the permeable pipe pile within 10 days was mainly attributed to the pile side friction, whereas the pile tip resistance made more contribution to the improvement of bearing capacity within 10-24 days. The excess pore water pressure of the pile-soil interface increased along with the depth of the pile. With the rapid dissipation of excess pore water pressure near the pile tip, the effective stress of soil gradually increased, and the pile side friction and pile tip resistance also increased. This study provides an improved insight into the design and construction of permeable pipe piles in soft soil foundation.

Key words: permeable pipe pile, fiber Bragg grating (FBG), bearing capacity, internal force of pile, excess pore water pressure