Tunnelling induces stress change and displacement in the ground. The excavation of a new tunnel in stratified soil can trigger different patterns of stress redistribution, which may adversely influence nearby tunnels. Research on multi-tunnel interaction has mainly been performed on the assumption of a uniform ground. The effects of different soil stratifications on tunnelling interaction remain poorly understood. In this paper, three-dimensional numerical parametric studies verified by previous centrifuge tests were carried out to analyse the twin tunnelling effects in two-layered soil. An advanced hypoplastic constitutive model that can capture stress-, path-, and strain-dependency of soil behaviour is adopted. Numerical cases investigated include perpendicular twin tunnelling in two sand layers with different relative densities and the location of the interface between the two sand layers. It is revealed that larger settlements and a wider surface settlement trough occur when tunnelling in two-layered soil strata than in a uniform ground. This is because of the wider and larger soil arch induced in two-layered soil strata. The structural response including tunnel deformation, induced bending moment, and induced hoop stress of the existing tunnel can be greater when tunnelling in layered soil strata than in a uniform ground owing to larger stress relief. Moreover, the combination of bending moment and hoop stress can exceed the M−N failure envelope of the structure in layered soil. A conventional simplified assumption of a uniform ground can underestimate of the influence of new tunnel excavation on existing tunnels, resulting in unsafe designs.

中文翻译：

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双层土层双隧道掘进三维数值分析


隧道开挖会引起地面应力变化和位移。在分层土中开挖新隧道可能会引发不同模式的应力重新分布，这可能会对附近的隧道产生不利影响。多隧道相互作用的研究主要是在均匀地面的假设下进行的。不同土壤分层对隧道相互作用的影响仍知之甚少。本文通过前期离心机试验验证的三维数值参数研究来分析双层土体中的双隧道效应。采用了先进的亚塑性本构模型，可以捕获土体行为的应力、路径和应变依赖性。研究的数值案例包括在具有不同相对密度的两个砂层中进行垂直双隧道掘进以及两个砂层之间的界面位置。结果表明，与均匀地层相比，在两层土层中开挖隧道时会出现更大的沉降和更宽的地表沉降槽。这是因为两层土层中产生了更宽更大的土拱。由于应力释放较大，在层状土层中开挖隧道时，现有隧道的结构响应（包括隧道变形、诱发弯矩和诱发环向应力）可能比在均匀地层中更大。此外，弯矩和环向应力的组合可以超过层状土中结构的 MN 破坏包络线。统一地面的传统简化假设可能会低估新隧道开挖对现有隧道的影响，从而导致设计不安全。