铁路悬索桥隧道式锚碇受载破裂力学行为研究

Damage behavior of tunnel-type anchorages of railway suspension bridges under loading

隧道式锚碇是悬索桥锚碇的一种主要类型,由于锚塞体与围岩形成复杂的受力体系,其承载机制尤其是受载破裂全过程的力学行为尚不十分清楚。基于ABAQUS建立岩体弹脆塑性损伤本构模型,该本构同时考虑岩体张拉和剪切破坏机制,能够较好地模拟岩体变形破裂全过程,拓展原本构模型的应用范围;通过损伤数值分析揭示不同埋深情况下隧道式锚碇的破裂力学机制。结果表明,隧道锚变形破坏存在显著的渐进破坏特征,埋深变化下破坏模式的转变与围压作用下岩体脆-延-塑性的转换特征相关;浅埋情况下围压较小,隧道锚体系"脆性"大,发生喇叭形的张拉-剪切破坏;深埋情况围压较大,体系"延性"增强,破坏模式转变为沿锚塞体与围岩接触界面的剪切破坏,其极限承载力较浅埋情况大幅度增加。隧道锚的喇叭形破坏面与传统认识的直线型破坏面存在明显差别,将直接影响其承载力计算模型的建立,因此在隧道锚设计计算中应关注破坏面的实际形态,这对其他类似锚固工程,如抗拔短桩或锚杆的承载力分析也有参考价值。

The tunnel-type anchorage is the primary anchorage type for suspension bridges. The anchor plug and the surrounding rock form a complex force system. The bearing mechanism and the complete mechanical damage behaviors of tunnel-type anchorages are still not very clear. An elastic-brittle plastic damage constitutive model for rocks is developed in finite element software ABAQUS. The damage model considering both the tensile and shear failure mechanisms can better simulate the rock deformation and failure process,and expand the application areas of the original model embedded in ABAQUS. The numerical analyses are conducted to reveal the mechanical damage behaviors of tunnel-type anchorages buried at different depths. The results show that the deforming of tunnel anchorages exhibits a significant progressive failure behavior. The change of failure modes influenced by buried depth is related to the confining pressure,and the increasing of confining stresses improves the ductility or plasticity of rocks. For the shallow buried tunnel-type anchorages with low confining stresses,the mechanical system is a little bit of brittle,so a horn-shaped failure surface and a composite mechanical mechanism of tensile and shear failure are found. For the deep buried cases with high confining stresses,the mechanical system has high ductility,the shear failure occurs at the interface between the anchor plug and surrounding rocks,and the limit bearing capacity has an evident increasing compared with the shallow buried cases. The investigated horn-shaped failure surfaces in this study are very different from the failure surfaces traditionally used in practical engineering,which may affect directly the establishment of calculation model of bearing capacity. Hence,the extra attentions should be paid to the actual failure form in the design of tunnel anchorages.