劲芯水泥土桩复合地基承载路堤失稳破坏模型试验

Model Test on Instability of Stiffened Deep Mixed Column-supported Embankment over Soft Soil

摘要:

劲芯水泥土桩可有效提高软土地基承载力，减小地基沉降和提高边坡稳定性。目前对于劲芯水泥土桩的研究主要集中在其承受竖向荷载条件下的工程特性上，对于路堤荷载下桩体失稳破坏模式与计算方法的认识尚不全面。开展1g重力场模型试验，对比研究了路堤荷载下天然地基、水泥土桩复合地基、劲芯水泥土桩复合地基路基变形、桩土应力、桩体应变、桩体破坏形态及路堤失稳模式，并评价了现有刚性桩复合地基稳定性计算方法对于劲芯水泥土桩复合地基承载路堤稳定性分析的适用性。结果表明：相较于水泥土桩，劲芯水泥土桩能有效约束地基土变形，路面沉降约为水泥土桩复合地基的61%~71%，坡外隆起约为12%~46%，进而显著提高路堤的稳定性。在路堤荷载下，劲芯水泥土桩表现出渐进式失稳破坏特征，桩体可发生纯压破坏、压弯破坏和弯曲破坏，且与桩体刚度和相对于路堤位置有关，桩体断裂位置与滑动面位置并未重合。等效抗剪强度法对于劲芯水泥土桩承载路堤稳定性分析具有一定的适用性和应用价值。

Abstract:

Stiffened deep mixed columns （SDMCs） can effectively increase bearing capacity， reduce settlement and enhance stability when they are used to improve soft soil. Currently， the researches on SDMCs have been mainly focused on the engineering properties of SDMC under vertical loading， leaving a gap in improving understanding of failure mode of SDMC under embankment load as well as its calculation approach. This paper conducted a series of 1g gravity scale-reduced model tests， including embankments supported by natural soft soil， deep mixed （DM） column-reinforced soil， and SDMC-reinforced soil. The instability of embankments supported by different foundations were analyzed through a comparison of deformation of embankment， stresses on column head and soil， strains in column， and failure modes of column. The applicability of the existing stability calculation methods were assessed. The results showed that the SDCM columns effectively restrained the soil deformation， namely， its settlement on the embankment crest and the ground heaving outside the embankment were approximately 61% to 71%， and 12% to 46% of those in the model test with DM columns， leading to a significantly enhancement on the global stability of the embankment. The SDCM columns failed progressively， and it may have failure modes of compression， a combination of compression and bending， and bending， depending on the column positions under embankment and column stiffness. The slip plane did not exactly go through the broken positions of column. The equivalent shear strength method had applicability to the stability analysis of SDMC-supported embankment as compared with other methods considered in this study.