静压沉桩后黏土中超孔压时空分布规律研究

为了解层状黏土在沉桩后桩周及桩端的超孔压对沉桩挤土效应的影响,采用现场原位试验和数值模拟方法,分析了桩土界面处超孔压的时空分布特征和上覆竖向有效应力随时间的变化规律,并在水力压裂理论和孔穴扩张理论的基础上引入修正剑桥模型,推导了桩周土体固结过程中桩土界面处上覆竖向有效应力和超孔压的修正计算公式。结果表明:从时间上看,在桩顶的外荷载作用下,超孔压随时间消散的同时,上覆竖向有效应力逐渐增大；成桩后30.d超孔压基本消散完毕,上覆竖向有效应力不再增长,地基土处于休止期。从空间上看,超孔压随桩埋深的增大而增大,在渗透性差的黏土层增长较快；不同荷载条件下,距桩心的水平距离和桩端的竖向距离越小,超孔压越大；靠近桩端和桩心的超孔压最大值与桩顶荷载大小呈负相关关系。

Study on spatiotemporal distribution of excess pore water pressure in clay after static pile sinking

To understand the influence of the excess pore pressure around the pile and at the pile end in layered cohesive soils after pile sinking on the soil compaction effect of pile driving, by using in-situ tests and numerical simulation methods, the spatiotemporal distribution characteristic of the excess pore pressure at the pile-soil interface and the variation law of the overlying vertical effective stress with time were analyzed. On the basis of the hydraulic fracturing theory and the cavity expansion theory, the modified Cam-clay model was introduced to derive the modified formula for calculating the overlying vertical effective stress and excess pore pressure at the pile-soil interface during the consolidation of soil around the pile. The results show that from the point of view of time, the excess pore pressure dissipates with time and the overlying vertical effective stress increases gradually under the external load of the pile top; After 30 days of pile formation, the excess pore pressure has basically dissipated, the overlying vertical effective stress no longer increases, and the foundation soil is in a resting period. From the point of view of space, the excess pore pressure increases with the increase of pile burial depth, and it increases faster in the clay layer with poor permeability; Under different load conditions, the smaller the horizontal distance from the pile center and the vertical distance from the pile end, the greater the excess pore pressure; The maximum excess pore pressure near the pile end and pile center is negatively related to the pile top load.