加芯水泥土桩复合地基桩土应力比计算方法研究

Research on calculation of pile-soil stress ratio for composite foundation reinforced by stiffened deep mixed piles

桩土应力比是研究复合地基的一项重要参数,目前的研究对象主要为常规复合地基,如搅拌桩、碎石桩等,而针对加芯水泥土桩的计算方法研究鲜有报道。从土体、水泥土及复合桩体单元变形模式出发,综合考虑桩体负摩阻力、桩顶和桩端刺入持力层的情况,分析了桩周土体、水泥土桩及复合桩体的压缩变形,导出了刚性基础下加芯水泥土桩复合地基芯桩、水泥土桩与土体3者之间的应力比的计算公式。并分析了加芯水泥土桩芯桩直径、芯桩桩长及水泥土桩桩长对桩土应力比的影响,其主要影响表现在随着加芯水泥土桩芯桩直径和桩长及水泥土桩桩长的增加,桩土应力比np亦逐渐提高。工程实例表明,计算结果与实测值具有较好的一致性,说明该方法具有一定的工程实用性,可为工程实践提供指导。

Pile-soil stress ratio is an important index in the research of composite foundation. Currently, the studies regarding the pile-soil stress ratio mainly focus on the general composite foundations, such as mixing pile and gravel pile. However, the theoretical calculation of stress concentration ratio of stiffened deep mixed（SDM） pile has been rarely reported. From the deformation modes of soil, cement and the composite pile element, the negative friction resistance of pile, pile cap and pile tip penetration to bearing layer is considered comprehensively, the compression deformations of soil around the pile, cement soil pile and composite pile body are analyzed, and a stress ratio calculation formulation is derived to describe the relationships among stiffened deep mixed composite foundation piles, cement soil pile and soil. Further, the effects of core pile diameter of stiffened deep mixed pile, core pile length and soil cement pile length on the pile-soil stress ratio are analyzed. It is found that the pile soil ratio increases with increasing the core pile diameter, length of stiffened deep mixed pile and pile length of cement soil. By comparing the computed results with the field data from a field test, the computed results and measured data agreed well and the reliability and feasibility of the proposed method was verified, which can be beneficial to guiding the actual practice.