上部结构刚度对桩基承台加防水板的影响

Influence of Superstructure Stiffness on Pile Foundation Cap with Waterproof Slab

基于弹性理论和变形协调关系推导了桩基承台加防水板时的桩土应力估算公式,采用ABAQUS建立了上部结构-桩基承台加防水板-地基共同作用模型和仅考虑桩基承台加防水板-地基共同作用模型,对比分析了上部结构刚度对地基反力、桩顶反力、基础底板内力与变形的影响,计算了不同位置处桩顶实际反力与设计反力的比值。利用"生死单元"技术模拟施工过程,研究了荷载分配比、单位荷载差异沉降、底板弯矩等随施工层数的变化规律。结果表明:荷载分配与桩-土刚度比、持力层硬度、柱距、防水板厚度等因素有关;防水板底土能承担20%左右的上部结构荷载,考虑上部结构刚度后板底反力分布更加均匀,防水板的"架越作用"不明显,角桩和边桩增荷而中部桩卸荷,基础底板差异沉降显著减小,承台最大弯矩截面由墙边处变为跨中处;逐层施工中桩分担的荷载逐渐增加,而防水板底土和承台底土分担的荷载逐渐减小,并且这种增加或减小的趋势逐渐减缓;上部结构刚度约束基础差异沉降的能力是有限的,考虑逐层施工后承台最大弯矩增加,防水板柱下板带最大弯矩减小,跨中板带弯矩始终很小且几乎无变化。

Based on the elastic theory and the deformation compatibility relationship, the pile-soil stress estimation formula for pile foundation cap with waterproof slab was deduced. The coaction model of superstructure-pile foundation cap with waterproof slab, and the coaction model of only pile foundation cap with waterproof slab were established by ABAQUS. The influences of superstructure stiffness on the foundation reaction force, pile-top reaction force and internal force and deformation of foundation floor were compared and analyzed. The ratios of actual reaction force to design reaction force at different locations were calculated. The construction process was simulated by using the "life and death element" technology, and the variation law of load distribution ratio, differential settlement of unit load and bottom bending moment with construction story were studied. The results show that the load distribution is related to pile-soil stiffness ratio, hardness of bearing layer, column spacing and thickness of waterproof slab, etc. The bottom soil of waterproof slab can bear about 20% of the load of superstructure. After considering the superstructure stiffness, the distribution of bottom reaction is more uniform, the overhanging effect of waterproof slab is not obvious, and corner piles and side piles increase the load, while the middle piles unload,the differential settlement of bottom decreases significantly, and the maximum bending moment section of the cap changes from the side of wall to the middle of span. The loads of pile increase gradually,while the loads of bottom soil for waterproof slab and cap decrease gradually in layer-by-layer construction, and the trends of increasing or decreasing gradually slow down. The ability of the superstructure stiffness to restrain the differential settlement of foundation is limit, and the maximum bending moment of cap increases after considering layer-by-layer construction, the maximum bending moment of waterproof slab column decreases, and the bending moment of mid-span slab is always small and almost unchanged.