下穿隧道开挖引起的挤土桩沉降控制分析方法

Analytical method for settlement control of displacement pile induced by undercrossing tunnel excavation

随着地下空间开发利用的立体式发展,地下近接工程中结构相互作用问题日益突显。针对盾构隧道下穿既有挤土桩问题,提出了基于岩土介质小孔扩张(收缩)理论的分析方法。通过基于统一砂黏土本构模型和大应变假设推导的小孔扩张-收缩排水解析解,建立了隧-桩相互作用力学模型;提出了隧道开挖影响下桩基的承载力衰减因子,并采用荷载-沉降曲线预测了桩基沉降。由分析结果可知,隧道地层损失引起的桩侧承载力减小、桩端承载力减小和桩端刚度损失,三者共同作用促使桩基发生沉降失稳,并提出了桩基的承载力控制准则、稳定控制准则和变形控制准则。此外,研究得到了桩基失稳时隧道地层损失与各因素之间的相关关系。其结果为揭示隧道与邻近结构相互作用机制、保障地下结构稳定性提供了有效的分析手段和必要的理论依据。

With the stereo development and utilization of underground space,problems related to structure interaction are increasingly important in underground approaching construction projects.This paper proposed an analytical method based on cavity expansion(contraction)theory in geomaterials to solve the problem of tunnel excavation under-crossing a displacement pile.By adopting the unified clay and sand model and the large-strain assumptions,a mechanical model for tunnel-pile interaction was established in regards to the two dimensional problem.With the influence of tunneling volume loss,a reduction factor of pile bearing capacity was proposed,and the load-settlement response was then employed to predict tunneling-induced pile settlement.The analyses indicated that tunnel volume loss induced the reductions of both pile shaft and pile end bearing capacities,as well as the stiffness of surrounding soil,which all led to pile failure.Additionally,relationships to link tunnel volume loss to tunnel-pile distance,bearing capacity reduction factor,initial safety factor,and soil initial state parameters were obtained at pile failure,which ultimately contributes to understanding of the mechanisms of tunnel-structure interaction and the stability of underground structure.