上覆卸荷对既有隧道围岩压力影响的数值模拟研究

Influence of Overburden Unloading on Existing Tunnel Surrounding Rock Pressure by Numerical Simulation

以厦门北动车运用所新建刘塘隧道上跨穿越既有杭深线铁路隧道的近接施工为背景,在FLAC3D数值平台上,对新建刘塘隧道的开挖过程展开精细化数值模拟。重点关注既有隧道衬砌上的围岩压力分布,并引入卸荷系数的概念,分析不同净距、不同交叉角度、不同跨度下卸荷系数的变化规律。数值模拟结果表明,上覆卸荷前后,作用在既有隧道衬砌上的围岩压力分布形态基本不变;若将卸荷前后围岩压力差值与原围岩压力的比值定义为卸荷系数,可得本工程的竖向卸荷系数βV为0.271,水平卸荷系数βH为0.153。进一步研究表明,竖向及水平卸荷系数随交叉角度α的增大呈大致线性增大、随净距跨度比KH的增大呈大致线性减小、随上下跨度比KD的增大呈二项式非线性增大趋势。上述研究成果可为类似工程的设计与施工提供技术参考。

Based on the adjacent construction project of newly-built Liutang Tunnel over-crossing the old Liutang Tunnel in Xiamen North Station, the excavation process of newly-built Liutang Tunnel was carefully simulated on the numerical platform of FLAC^3D. The pressure carried by the existing tunnel lining was focused during simulations, and the unloading coefficient was introduced. The variation unloading coefficient was further studied due to different clear spacing, crossing angles and spans. The simulation results showed that the lining pressure distribution upon the existing tunnel remained unchanged in general before and after overburden unloading. We defined the unloading coefficient as the variation ratio to the original lining pressure, and the vertical and horizontal unloading coefficients for this project were 0. 271 and 0. 153 respectively. Further simulation results showed that the unloading coefficients increased linearly with the crossing angle α, decreased linearly with the spacing ratio KH and increased binomially with the span ratio KD. These results could provide some reference for the design and construction in similar scenario.