砂土中隧道垂直下穿既有管线的数值模拟

为研究隧道施工条件下管线的变形，通过开发颗粒流程序及利用室内管线加载-挠度试验建立了管线宏细观参数之间的关系.基于PFC2D建立了隧道-土体-管线的数值模型，模拟砂土中隧道垂直下穿既有管线过程中管线的变形位移.通过数值模拟分析了地层损失率及管线与隧道间距对模拟结果的影响规律.结果表明:随着地层损失率的增加及管隧间距的减小，管线中间的下拉效应与距管线中点35倍隧道直径处的上拱效应越明显；管线中部上覆附加应力会随地层损失率的增大及管隧间距的减小而增大，同时对应管底土压力则迅速减小并稳定在一较小值；管线与管底土层沉降槽宽度系数比值(ip/i)与地层损失率成正比，而与管隧间距成反比，最大值可达到24.

Numerical Simulation on Effects of Vertical Tunnel Excavation on Underground Pipeline in Sand

In order to investigate the deformation of pipeline during tunnel excavation， the relations between the macroscopic and microscopic parameters of pipelines were formed based on laboratory deflection test and PFC programming. Based on the PFC2D， the numerical model of the tunnel soil underground pipeline was established for simulating the deformation of pipelines during tunneling in sand， and the effects of ground loss and tunnel pipeline space were examined. The numerical results showed that the behavior of pipelines is negative downdrag in the middle and positive downdrag at 35 times the diameter of tunnel from the middle of pipelines， which are greater under the increase of ground loss and decrease of tunnel pipeline space. With increasing ground loss and decreasing tunnel pipeline space， the additional load on the top of pipeline increases and the vertical earth pressure decreases quickly at the bottom of the pipeline， which trends to reach a final value. The ratio of ip/i as the width coefficient is proportional to the ground loss， and inversely proportional to the tunnel pipeline space， where the maximum value of 24 can be reached.