管桩与袋装砂井组合型复合地基特性研究

Study on Characteristics of Composite Foundation with Pipe Pile and Sand Bag Well

管桩与袋装砂井组合型处理方法已应用于软土复合地基,以解决高速公路桥头跳车、工后沉降等问题,但其固结、沉降与稳定性仍不明确。针对以上问题,依托广东某标段工程,基于有限元建立了复合地基模型,通过改变处理方法分析了4种模型的固结、沉降、稳定性和桩侧摩阻力的变化规律。结果表明:仅打设袋装砂井的超静孔隙水压力会反弹,打设管桩会使反弹现象消失,两者组合处理的超静孔隙水压力小且消散很快,均先增大至12kPa后减小,而先打设管桩的消散更快。组合方法处理后的地基沉降小且避免了沉降产生的危害,先施工管桩的沉降要小于先施工袋装砂井,两者沉降差随着与路堤中心距离的增大先增大后减小。不同加载施工期的稳定性差别较大,打设管桩后的安全系数增幅要大于仅用袋装砂井,施工顺序对路堤稳定性影响很小。桩侧摩阻力与桩顶荷载呈正相关,中性点位置随路堤填筑先下降后向上移动,在100d后再下降;当路基填筑完成后,此时土体固结是影响桩侧摩阻力的主要因素。

The combined treatment method of pipe pile and sand bag well has been applied to soft soil composite foundation to solve the problems of jumping traffic at the bridge head and post-work settlement of highway, but its consolidation, settlement and stability are still unclear. For the above problems, based on a tender section project in Guangdong province, a composite foundation model was established based on finite element, and the change law of consolidation, settlement, stability and pile side friction resistance of the four models were analyzed by changing the treatment method. The results show that the excess pore water pressure will bounce back by only setting sand bag wells. The rebound phenomenon disappears when the pipe piles are installed. The excess pore water pressure of the combined treatment is small and dissipates quickly, increasing to 12 kPa first and then decreasing, while the dissipation is faster when the pipe pile is installed first. The settlement of the combined treatment is small and avoids the hazards generated by the settlement basin, and the settlement of the pipe pile first is smaller than that of the sand bag well first, and the settlement difference between the two increases and then decreases as the distance from the embankment center increases. The stability of the different loading construction periods differs greatly, and the increase of safety factor after laying pipe piles is greater than that of sand bag wells only, and the construction sequence has little effect on the embankment stability. The pile side frictional resistance is positively correlated with the pile top load, and the neutral point position first decreases and then moves upward with embankment filling, and then decreases after 100 days. When the roadbed filling is completed, the soil consolidation is the main factor affecting the pile lateral friction resistance at this time.