In the bored precast pile construction method, precast concrete pile or steel pipe pile is used, and small sized piles also apply to this method.
The objective of this study is to develop an effective pile end shape for a small-diameter steel pipe pile, which can work even if the stiffness of the cement paste around the pile tip would be insufficient. Laboratory experiment for static axial compressive load test of single pile in which the tip was covered with plaster was performed. The end resistance was larger than that of a bared pile, but when the displacement progressed, the resistance decreased because of destruction of the root part. The behavior of the end resistance and relationship of the strength of the root part were discussed, and a simplified calculation method was proposed.
The bored precast pile method is a major pile construction method in Japan. The application number of this method is increasing in urban areas because of less noise and low vibration. Recently, small sized piles also apply to this method for small building's foundations such as detached residences or retaining walls.
It is necessary to build a homogeneous and strong root solidifying part in the pile end zone. The root part is designed to have sufficient strength, and is managed as strictly as possible. However, the strength of the root part may be insufficient due to the unevenness and dispersion of the ground layer, and some errors of the control of the installation. If the pile end is fixed to a hard layer, such as dense sand or gravel layer, the sufficient end resistance can be obtained because it is relatively easy to build the root hardening part with good quality. However, in the case of a soft cohesive layer or saturated medium sandy layer, the end resistance can be short. It is surmised that the cause of this phenomenon is destruction of the root part, and it occurs due to weakness of the root part and/or insufficient stiffness of the soil around the pile end.
