饱和黏土中静压桩桩周土体强度时效性分析

Time-dependent analysis on strength of soil around jacked pile in saturated clay

天然饱和黏土中静压桩在沉桩过程中对土体造成巨大的挤压,致使桩周土体产生较高的超孔隙水压力,沉桩结束后随着桩周土体的逐渐固结,土体强度表现出明显的时效性.为研究饱和黏土中静压桩沉桩后桩周土体强度的变化规律,基于K0-MCC模型并考虑了土体初始各向异性与诱发各向异性对桩周土体强度的影响,推导出柱孔不排水扩张后桩周土体应力及超孔压的解答,并根据轴对称固结理论推导了静压桩桩周孔压消散的理论解答.在此基础上,考虑桩周土体在固结过程中的松弛效应,对沉桩结束后桩周土体强度的时变效应进行了解析,并通过离心机模型试验验证了该解答的合理性.结果表明,该解答能够较为合理地预测沉桩结束后桩周土体强度与超孔压的变化规律,而土体超固结比、静止侧压力系数和土体有效内摩擦角等因素对桩周土体强度变化存在一定的影响.饱和黏土中静压桩的承载力具有时效性,静压桩周土体强度时变规律的解答能够为静压桩时变承载力的计算提供理论依据,具有重要的现实与科学意义.

Considering the initial and induced anisotropy of the soil, the solutions to the stress and pore water pressure around a jacked pile, based on K0 modified Cam-clay model （ K0-MCC） , were derived by using cylindrical cavity expansion to simulate the pile installation. Meanwhile, with the axial consolidation theory and the elastic-plane hypothesis for the reconsolidation of the soil around the jacked pile, governing equation for consolidation was established. The variation of the soil strength with reconsolidation time was studied with relaxation effect based on the above studies, and the theoretical solution was then verified by the centrifuge model tests. The results show that the presented theoretical method can properly predict the time-dependent soil strength and the change of excess pore water stress after the pile installation, and the over-consolidation ratio, static lateral pressure coefficient and effective angle of internal friction of soil also have influence on the time-dependent soil strength around the pile. The solution of time-dependent strength of soil can provide theoretical basis for the prediction of time-depended bearing capacity of jacked pile in saturated clay.