浅埋大断面黄土隧道围岩变形时空效应分析

Space-time Effect of Surrounding Rock Deformation in Shallow-depth Large Section Loess Tunnels

以大西客运专线某隧道浅埋段为工程背景,针对三七微台阶法施工条件下的围岩变形特性进行了现场测试分析。实测结果表明:隧道在开挖的过程中其围岩变形受时间、空间效应的影响,整个时程曲线呈"厂"型,增长历时约25天;隧道纵向开挖面的影响距离大约为2倍的洞径;监测断面距离开挖面1倍的洞径时,拱顶下沉释放率均达到了70%以上,仰拱开挖时,拱顶下沉释放率增加了约30%;二次衬砌的合理施作时间约为隧道开挖后在初期支护施作16～19天后。该结果对深入了解类似隧道围岩变形规律,确定合适的支护时机很有意义。

Taking shallow section of the Xinzhou tunnel in Datong-Xi＇an passenger line as the engineering background, this study uses site monitoring to measure space-time effect of surrounding rock deformation in three micro bench seven step excavation method. Results show： deformation of surrounding rock is affected by space-time under excavation; the time curve is in inverted “L ” shape and may last about 25 days; the impact distance of excavation face is about twice of the tunnel diameter longitudinally; when the distance between monitoring sections and excavation face is equal to the tunnel diameter, release rate of the vault crown settlement reaches more than 70%;when the invert is excavated, release rate of the vault crown settlement increases about 30%; the reasonable time of secondary lining construction is 16-19 days later after initial support construction. It is significant for comprehending the surrounding rock deformation in details to determine the reasonable support time.