Engineering behavior of prebored precast prestressed concrete piles (PPPCPs)

Abstract

Prebored precast prestressed concrete pile (PPPCP) is a new pile type imported from Japan to Macau. During the construction of PPPCP, the soil at the proposed pile location is agitated to a loose state and then mixed with cement grout before the installation of a precast prestressed concrete pile. It is an environmentally friendly technique which generates little noise to nearby residents and little disturbance to nearby structures during construction. Moreover, the material cost of PPPCP can be 30% less than that of the steel H-pile with similar design load-carrying capacity. However, the engineering behavior of PPPCP is not well analyzed outside Japan. In this research, a comprehensive study is carried out on two fully instrumented trial PPPCPs and three working PPPCPs installed in Macau. Full-scale pile load test data are available for analysis and the engineering behavior of this new type of pile is investigated.

In this study, a new method that used to estimate the ultimate capacity of PPPCP from non-failing load tests is developed. As for the load-settlement characteristics, an empirical equation is proposed to evaluate the elastic settlement of PPPCP and a hyperbolic function is recommended to simulate creep settlement. The shaft and tip resistance of the PPPCP are investigated and the separation between the shaft and tip resistance is made. The distribution and development of shaft resistance along the pile shaft is analyzed and the load transfer mechanism of PPPCP is better understood. A new correlation between the SPT-N value, the effective vertical stress and the unit shaft resistance of PPPCP is proposed. Furthermore, a numerical model is established to simulate the behavior of PPPCP under static load. A PLAXIS 2D model is used to serve this purpose and the simulated load-settlement behavior exhibits a good agreement with the results of static pile load tests. It is observed that the load distribution along the pile shaft simulated by the PLAXIS 2D axisymmetric model is generally in good agreement with the measured distribution. It seems that the PLAXIS 2D model can provide a good simulation of the load transfer mechanism of PPPCP with reasonable accuracy. After this study, the engineering behavior of the newly introduced pile, i.e. PPPCP, is better understood, and this would be beneficial for promoting its application in the industry.