刚性桩加固高速公路软基性状分析
Behaviors of rigid piles for reinforcing highway embankments in soft soils
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摘要: 刚性桩在高速公路软土地基处理中得到了广泛应用,但目前对其承载变形机理还缺乏深刻认识。采用数值方法对端承型桩及摩擦型桩在路堤填筑及软基固结过程中桩土应力比、桩土沉降、桩身轴力、负摩阻力及中性点深度的发展变化规律进行了分析。分析结果表明:①不论端承型桩还是摩擦型桩,由于其刚度远大于桩间土刚度,因此绝大部分路堤荷载由桩承担,桩间土仅承担了少部分路堤荷载。桩间土土压力随着路堤填筑和软土固结经历了先增大、然后减小、最终趋于稳定的过程;②路堤填筑及软基固结过程中,端承型桩仅发生很小的沉降,其大部分沉降发生在路堤填筑过程中,摩擦型桩的沉降则较大,其大部分沉降发生在路堤填筑完毕之后的软基固结过程中。端承型桩大部分区段桩身沉降小于桩侧土沉降,而摩擦型桩大部分区段桩身沉降大于桩侧土沉降;③无论是端承型桩还是摩擦型桩,在路堤填筑过程中,桩身轴力及负摩阻力增加均较快,而在软基固结过程中增加则较慢。端承型桩的大部分桩段存在负摩阻力,摩擦型桩的负摩阻力分布区段则较短;④在路堤填筑及软基固结过程中 , 桩身中性点位置经历了比较复杂的变化过程。Abstract: Rigid piles have been widely used to reinforce highway embankments in soft soils due to their rapid construction, low costs, and small total and differential settlements, while their mechanism has been still incompletely understood till now. A numerical analysis is conducted to evaluate the variation of the soil stress concentration ratio, pile and soil settlements, pile shaft axial forces, negative skin friction and neutral plane for end-bearing piles as well as floating piles during the embankment filling and the consolidation of soft soils. The results indicate that the stress concentration ratio varies with the embankment filling and the consolidation of soft soils, and most of embankment load is born by the pile owing to that the pile stiffness is significantly greater than that of soft soils. The end-bearing pile settles a little and most of the settlement occurs during the embankment filling while the settlement of the floating pile is much greater and most of the settlement occurs during the soil consolidating. The settlement of most part of the end-bearing pile shaft is greater than that of the surrounding soil, but the settlements of most part of the floating pile shaft is less than that of the surrounding soil. The pile axial force and negative skin friction, for the end-bearing pile and the floating pile, develops more quickly during the embankment filling than during the soil consolidating. Negative skin friction develops along most part of the end-bearing pile shaft while only a small part for the floating pile. The location of the neutral plane exhibits a complicated variation.