Driving response of an open-ended PHC pipe pile group in silty fine sands

Construction response of pipe piles has an important impact on their drivability and load-carrying behavior . However, very limited case histories of the construction response of pipe pile groups are available. For this purpose, field tests on soil squeezing and plugging responses to pile driving are carried out in silty fine sands in an open-ended pre-stress high strength concrete (PHC) pipe pile foundation of a power plant. In-situ soil lateral displacement, pore water pressure and soil plug length are measured. Considering the non-orientation feature of the lateral displacements, the resultant lateral displacements and movement azimuth angles are analyzed by using a data processing method derived from the working principles of pendulum-type inclinometers. Meanwhile, real-time changes in the pore water pressure during the whole process of pile driving are measured by using an automatic dynamic data acquisition system with a sampling time interval of 28 s. The results show that in silty fine sands changing gradually from loose to dense state, the soil squeezing and plugging effects decrease with the increasing penetration depth. The squeezing effect of pipe pile groups decreases due to the soil densification induced by pre-driven piles. The squeezing effect in the interior of the pile group is more significant than that in the exterior of the pile group. A short-term buildup of the pore water pressure is induced around the pile toe, and it is not accumulated during the construction of the pile group.