A series of three-dimensional parametric finite element analyses were carried out to investigate the induced ground surface settlement during the excavation of perpendicularly under and above crossing twin tunnels. Both transverse and longitudinal settlements are investigated and presented in this study. The results suggest that the larger the cover depth, the wider the transverse settlement trough and the more the position of maximum settlement shifted towards the existing tunnel centerline. It is also evident that the lower the cover depth the higher the settlement increase rate is. Other important findings are (i) both transverse and longitudinal tunnel displacements increase with an increase in the pillar distances when the upper tunnel is excavated first and vice-versa, and (ii) the maximum transverse settlement occurs at the centerline of the existing tunnel whereas the maximum longitudinal settlement occurs at and around the excavation face. Furthermore, the effect of various stages of the crossing tunnel excavation and tunnel sizes are also examined, and it is observed that the transverse settlement trough becomes wider and deeper as the new undercrossing tunnel advances away from the existing upper tunnel. It is also found that as the diameter of a tunnel increases, the transverse settlement of both the existing tunnel and the newly excavated crossing tunnel increases regardless of the excavation sequence.

中文翻译：

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垂直穿越双隧道引起的地面沉降参数化研究

为了研究垂直上下交叉双隧道开挖过程中引起的地表沉降，进行了一系列三维参数化有限元分析。本研究对横向和纵向沉降进行了调查和介绍。结果表明，覆盖深度越大，横向沉降槽越宽，最大沉降位置越向既有隧道中心线偏移。还可以看出，覆盖深度越低，沉降增长率越高。其他重要的发现是（i）当首先挖掘上部隧道时，横向和纵向隧道位移随着支柱距离的增加而增加，反之亦然；（ii）最大横向沉降发生在现有隧道的中心线，而最大纵向沉降发生在开挖面及其周围。此外，还检查了穿越隧道开挖的各个阶段和隧道尺寸的影响，并观察到随着新的下穿隧道远离现有上部隧道，横向沉降槽变得更宽更深。研究还发现，随着隧道直径的增加，无论开挖顺序如何，现有隧道和新开挖的穿越隧道的横向沉降都会增加。