长短桩布桩方式对复合地基沉降变形影响研究

针对蒙华铁路岳阳段软土和松软土地基问题，为了有效控制地基沉降，提出了采用分离式布桩和交叉式布桩的长短桩复合地基加固方案。基于离散元颗粒流仿真技术分析两种布桩形式、不同桩间距对软土地基沉降的影响规律和机理，提出合理的加固方案并通过现场测试验证。研究表明：① 分离式布桩和交叉布桩下，复合地基最大沉降位移/桩体最大沉降位移均与桩间距均呈指数函数分布；② 分离式布桩复合地基最大沉降位移出现在地基面上两种桩型的衔接处，桩体最大沉降位移出现在两种桩型衔接处的多向搅拌桩桩顶位置。③ 交叉式布桩复合地基最大沉降位移出现在地基面上的线路中心线处，桩体最大沉降位移出现在加固地基顶面中线附近的多向搅拌桩桩顶。④相同桩间距条件下，分离式布桩复合地基沉降和路基面宽度范围内地基的不均匀沉降量明显小于交叉式布桩复合地基。

Influence of layout and spacing of long and short piles on deformation of composite foundation

Aiming at the problem of soft foundation in Yueyang section of Menghua Railway for coal transportation, and in order to control the foundation settlement effectively, two composite foundation reinforcement schemes reinforced by long and short piles of separated and crossed layouts are put forward. The influence law and mechanism of two pile layouts and pile spacing on settlement of foundation are analyzed by discrete element particle flow simulation. Based on this, a reasonable reinforcement scheme was proposed and verified by field test. The results showed that:(1)for both layouts, the maximum settlement displacements of the foundation and the pile body were exponential relation with pile spacing. (2)The maximum settlement of the composite foundation reinforced by piles in separated layout appeared at the junction of long and short piles on the foundation surface. The maximum settlement of pile bodies occurred at the top of the multi-direction mixing pile at the junction of long and short piles. (3)The maximum settlement of the composite foundation with piles in cross layout appeared at the center line of the foundation surface and the maximum displacement of the pile body occurred at the top of the multi-direction mixing pile near the middle line of the foundation surface. (4)Under the same pile spacing, for the composite foundation reinforced with piles in separated layout, it had more even settlement within the subgrade surface and less settlement than the foundation reinforced with piles in cross layout.