求水山隧道下穿机荷高速段新奥法施工有限元计算

Finite element calculation of NATM construction of Qiushui mountain tunnel beneath Jihe expressway

结合求水山隧道的暗挖法施工方案,对软土地区浅埋隧道下穿高速公路的施工过程进行了有限元模拟,以用于评价按该施工方案施工时对其上部高速公路的影响。由于该段隧道最小埋深仅4m,且上部还有高速公路车辆荷载,因此,在设计时采用了新奥法结合管棚工法的方案。有限元建模使用平面应变单元,通过引入应力释放分析步和使用追踪单元等方法充分体现了新奥法的特点,并通过设置耦合和弹簧的方法实现了管棚工法的模拟,在计算中还考虑了开挖顺序和支护顺序的影响。研究结果表明:对于上部有荷载的浅埋暗挖隧道,控制衬砌的水平向变形能改善衬砌环的工作状态,因此,可显著减少开挖引起的隧道顶面沉降,新奥法结合管棚工法可较好地控制该类型隧道开挖引起的地表沉降变形。

Based on the scheme of underground excavation of tunnel in Qiushui mountain, a finite element model of a shallow buried tunnel beneath an expressway in soft soil region is established, so as to evaluate the effect of tunnel excavation on the expressway above. Considering the minimum embedded depth of the tunnel which is only 4 m and vehicle load on the surface ground of the expressway, a method combined new Austrian tunneling method（NATM） and umbrella arch method（UAM） is put forward in the design. Analysis is performed using plane strain finite element model, which shows the characteristics of NATM by using stress release steps and tracing element. The UAM is simulated by using coupling constraint and spring element. The excavation sequence and support sequence are also taken into consideration in the analysis. As a result of this study, controlling the lateral deformation of the tunnel lining can reduce the settlements of ground surface effectively during excavation; and the method combined NATM and UAM is applicable to shallow buried tunneling especially in soft soil region.