穿越软土层嵌岩桩筏基础沉降特征与计算方法

结合某双塔高层建筑核心区桩筏基础和核心区外独立承台桩基础沉降变形监测资料,分析了嵌岩桩筏基础的沉降特征。结果表明,双塔核心区嵌岩桩筏基础沉降变形的整体性较好,沉降随施工加载过程增长较为稳定,而核心区外嵌岩桩基础的沉降对主楼施工和环境条件(如地下水)较为敏感,施工中出现了桩体上浮现象。根据桩顶荷载计算的嵌岩桩桩身压缩量与实测沉降相比,实测值远大于计算值。考虑嵌岩桩施工和桩筏基础工作特点,提出了穿越软土层的嵌岩桩筏基础沉降的两个主要影响因素:沉渣效应和桩侧负摩阻。在此基础上,提出了考虑沉渣和桩侧阻影响的桩筏基础沉降估算方法,并通过本工程及文献中的工程实测对提出公式的适用性进行了检验。

Settlement of piled raft foundation embedded in rock and its calculation method

Based on the settlement monitoring data of two piled rafts under a twin-tower building,the settlement characteristics of piled raft foundation is examined. It is shown that the piled raft settles as a whole underloading, while the settlement of piles under individual plate, which is located outside the tower areas, is sensitive to changing of the adjacent loading and ground water level. By comparing the measurement with the calculated settlement, it is found that the measured settlements are much greater than the calculated values. Then, two influential factors are proposed, bottom sediment in pile and negative skin friction on pile, to revise the settlement calculation equation for piled raft foundation penetrating thick soft soil layers. Finally, the proposed method and the suggested parameters are checked through two real cases.