CFG桩复合地基具有较好的环保效益,近年来在软基处理中推广迅速。鉴于天然地基自身较差的工程特性,加之CFG桩施工扰动易引发表层土持力性能进一步弱化,受荷状态下刚性的CFG桩与桩间土易形成过大的桩-土应力比,褥垫层结构破坏风险增大,不利于复合地基协同受力。研究提出对截桩面下约50 cm厚剧烈影响区土层采用压实碎石换填,再铺设水泥土垫层而形成新型嵌入式褥垫层结构,以改善CFG桩复合地基持力性能,得到以下结论:①基于单桩复合地基现场载荷试验对比分析,采用嵌入式褥垫层测得的桩-土应力比显著低于常规平铺褥垫层,极限载荷下桩-土应力比较常规褥垫层的22.9降至13.8,降幅约40%,且全过程桩-土应力比曲线波动相对平缓,尤其是达到极限承载力后无陡降,有利于地基安全受荷;②采用数值试验手段模拟CFG群桩复合地基竖向受荷特性,嵌入式褥垫层对桩间土压缩层起到了显著的综合强化作用,既有效减小了桩向褥垫层的相对刺入,也使得褥垫层的变形形态更均匀平整,局部刺入和翘起得到有效缓解,避免了桩-土应力比过大对褥垫层结构的破坏;③嵌入式褥垫层条件下不同部位CFG桩的水平变形状态更优,顶部较强的约束将CFG桩受力模式由接近“悬臂式”变为接近“简支式”,对复合地基边桩和角桩的变形受力状态改善显著。

The CFG pile composite foundation offers notable environmental advantages and has seen extensive utilization for foundational stabilization in recent years. Surface soil load-bearing capacity deteriorates due to the inferior engineering properties of natural foundations, coupled with disruptions originating from CFG pile construction. Upon load application on the composite foundation, the CFG piles, behaving as rigid bodies, can easily cause an excessive pile-soil stress ratio, which is detrimental to the composite foundation’s interaction and inflicts damage upon the cushion layer. In view of this, we put forward the substitution of the 50 cm thick severely disturbed topsoil with compacted crushed stones, followed by the application of a cement-soil cushion to establish an innovative embedded cushion layer structure, geared towards the augmentation of the CFG pile composite foundation’s bearing capacity. The findings are as follows: in-situ load tests on single CFG pile composite foundation revealed that the pile-soil stress ratio within the embedded cushion layer was considerably less than that in traditional cushion layer conditions under the ultimate load, dropping from 22.9 to 13.8, a decrease of approximately 40% compared to traditional cushion layer conditions. Additionally, the pile-soil stress ratio curve was smoother, with no significant precipitous decline in pile-soil stress ratio after reaching ultimate bearing capacity, which is favorable for the foundation’s secure loading. Mathematical simulation methods were employed to model the vertical load characteristic of the CFG pile group composite foundation. The embedded cushion layer contributed significantly to the comprehensive fortification of the compression layers, thereby mitigating the piles’ relative penetration into the cushion layer. This resulted in a more uniform deformation of the cushion layer, effectively curtailing local penetration and uplift. Damage to the cushion layer structure caused by extreme pile soil stress ratios could be circumvented accordingly. Lastly, the embedded cushion layer enhanced the horizontal deformation state of CFG piles at different parts. The increased constraint at the top transformed the stress pattern of CFG piles from an ‘approximate cantilever’ to being ‘approximately simply supported’, thereby ameliorating the deformation and stress state of the side and corner piles.