软黏土中PHC管桩打入过程中土塞效应研究

当开口管桩打入土层中，土体进入桩内形成土塞，土塞效应对桩的打入特性和承载能力具有重要影响。基于上海典型软土地基中长PHC桩的现场试验，统计分析3个不同场地共44根桩打桩过程中的土塞数据，探讨软土地基中PHC桩打桩过程中土塞长度与内径之比、土塞增量与桩打入深度增量之比(IFR)随打入桩长与内径之比变化的规律，并线性拟合出土塞增量与桩打入深度增量之比与土塞高度和桩打入深度之比(PLR)的经验公式。研究表明，大部分PHC桩在打桩过程中，土塞部分闭塞，桩从浅部较硬土层打入较软土层，IFR值减小，土塞闭塞作用大；桩从较软土层打入深部较硬土层，IFR值逐渐增大，土塞闭塞作用小，且土塞长度增量与桩打入深度增量之比与土塞长度与桩打入深度之比基本呈线性关系。

Soil plugging effect of PHC pipe pile during driving into soft clay

Both the driving response and the bearing capacity of open-ended piles are affected by the soil plug that forms inside the pile driving. Field tests are conducted to investigate the plugging behavior of long PHC pile during driving into soft clay. Based on the field tests of long PHC pile in Shanghai soft foundation, soil plug data of 44 piles in three different fields are analyzed. For the PHC piles, the soil plug length is continuously measured during pile driving, allowing calculation of the incremental filling ratio (IFR) and the plug length ratio (PLR) for the pile. The test results show that normalized plug length (the ratio of plug length to pile inner diameter) and IFR vary with normalized pile length (the ratio of pile penetration depth to pile inner diameter) for different types of piles. It is shown that the value of IFR decreases for long PHC pile driving through shallow soil layer into deep soft soil, and the value of IFR increases for long PHC pile driving through deep soft soil into bearing stratum (fine sand). A relationship between IFR and PLR is proposed. The relationship between IFR and PLR allows the quick estimation of IFR based on the measuring data of PLR.