不对称双连拱海底隧道施工引起的地层变形分析

Asymmetric double-arch subsea tunneling-induced ground deformation analysis

在目前众多的预测隧道开挖引起的地层变形的方法中,经验公式法最为简便,也是目前应用最为广泛的方法,为此介绍了多种预测隧道开挖引起的地层沉降和水平位移的经验公式。并以青岛胶州湾海底隧道不对称双连拱断面为工程背景,由位于主隧道与匝道交叉口段的典型断面ZK2+800.78的几何参数和地质资料构建三维数值计算模型,采用岩土体工程通用有限差分软件FLAC3D进行动态施工三维数值模拟。通过对FLAC3D模拟和各经验公式计算的地层沉降和水平位移的对比分析,评价了FLAC3D软件和各经验公式在不对称双连拱隧道断面地层变形预测中的适用性。结果表明,当地层埋深较浅时,不同埋深地层的地层沉降和水平位移可近似用各经验公式来预测;但随着地层埋深的增大,各经验公式预测的偏差不断增大;经验公式只能对单一地层、单一隧道的地层变形进行估算,存在明显的局限性,而在预测复杂地质条件下不对称双连拱隧道断面开挖引起的地层变形时,FLAC3D较各经验公式有明显的优势。

Empirical formula method is one of the most popular-used methods to predict the soft ground deformation induced by tunneling.Various empirical formulae to predict the ground settlement and horizontal movement above shallow tunnels are introduced.Aiming at the asymmetric double-arch tunnel engineering that lies at Jiaozhou Bay in Qingdao,the section ZK2＋800.78 which is located in the intersection between main tunnel and ramp tunnel is chosen as a typical cross-section,a three-dimensional model for numerical analysis is established according to geometrical parameters and geological information of the typical cross-section;and dynamic construction process is simulated with finite difference software fast Lagrangian analysis of continua in 3D（FLAC3D）.By comparative analysis of the ground settlement and horizontal movement calculated with FLAC3D program and these empirical formulae,the applicability of these methods to predict the ground deformation above asymmetric double-arch tunnel is discussed and evaluated in detail.It concludes that when the strata are in shallow levels,the ground settlement and horizontal movement can be forecast with these empirical formulae approximately.The results also show that the deviation of these empirical formulae increases with the increase of stratum depth.There is a remarkable shortcoming for these empirical formulae that they can only be used to estimate the ground deformation above a single tunnel in a single stratum.FLAC3D has its clear superiority in predicting the ground deformation above asymmetric double-arch tunnel under complicated geological condition.