基于间距折减法浅埋小净距交叉隧道安全性分析

为解决交叉隧道的安全性评定问题,类比边坡工程中的强度折减法,以既有隧道允许的最大沉降值为判据提出交叉间距折减法。应用FLAC^3D软件模拟探究了不同覆土厚度、交叉角度对上部既有隧道的影响规律。当交叉角度为90°,覆土厚度分别为15、20、24、30 m时的临界交叉间距为3、4.5、7、11 m。当覆土厚度为26 m,交叉角度分别为0°、30°、45°、60°、90°时的安全净间距为6.8、7.6、8.9、8.1、7.4 m。结果表明,新建隧道对既有隧道的影响随覆土厚度增加而增大,随交叉角度增大呈现先增大后减小的趋势。为验证方法的合理性,以盘道岭隧道为背景对3种支护方案进行了交叉间距折减检验进行安全性评估。现场监测表明,开挖前进行的管棚支护较好地控制了对上部公路隧道的影响。

Safety Analysis of Shallow Intersecting Tunnel with Low Net-distance Based on the Method of Spacing Reduction

To evaluate the safety of intersecting tunnel, a new method of spacing reduction with criterion based on allowable maximum settlement of existing tunnel has been proposed. The principle of the new method is similar to the strength reduction method in the calculation of slope stability coefficient. In this paper, the effect rules of thickness of covering soil and cross angles on existing tunnel are studied by using FLAC^3D software. When the cross angle is a fixed value of 90° and the thickness is 20 m, 23 m, 26 m, 30 m respectively, the safety spacing is 2.8 m, 5 m, 7.6 m, 11 m. As the thickness is a fixed value of 26 m and the cross angle is 0°, 30°, 45°, 60°, 90° respectively, the safety spacing is 6.8 m, 7.6 m, 8.9 m, 8.1 m, 7.4 m. The result shows that the effect of new tunnel on existing is in proportion to thickness of covering soil and increases at the beginning and then decreases with the increase of cross angle. Taking the Pandaoling tunnel as background, the safety of three different kind of support scheme were examined using the method of spacing reduction. Field monitoring results show that the pipe shed support before the excavation has effectively controlled the influence of new tunnel on existing.