Abstract:

Since deep penetration large diameter steel pipe piles have been widely used in platform foundation, pile drivability analysis and blow count prediction play an important role in pipe driving. Research results show that during driving pile by a hammer, the continuous impacts will cause reduction of the strength of the soil around the pile and make the pile penetration easier. This phenomenon is called the fatigue effect. The soil strength fatigue leads to the prediction blow counts are always more than the data. However, it is all known that much more blows are needed in the subsequence driving process. The soil consolidation and strength restoration make the subsequence driving difficult. In order to explain the phenomenon, the mechanism of soil fatigue and restoration is analyzed based on the consolidation theory in soil mechanics. A program has been established based on the one dimensional wave equation, pile and soil interaction model and soil consolidation theory, which consider the soil fatigue effect and strength restoration in pile driving analysis. By simulating the practical pile driving records of blow account versus penetration of several cases, the advantages of the model are identified. The calculation results show that the model of quadratic distribution with penetration can better simulate the pile driving records. And the proposal method to estimate the ratio of the excess pore water pressure converting to effective stress is reliable.

Key words: drivability analysis, wave theory, soil fatigue, strength restoration