软岩浅埋隧道施工工法比选

目前在高速公路软岩浅埋隧道施工中均不同程度地出现了围岩坍塌、地表产生大面积沉降等问题。广福隧道某浅埋段，地质条件复杂，断面大、岩性差，受构造影响比较严重，而且顶板厚度比较薄，易发生坍塌、冒顶现象。为确保浅埋段隧道的施工安全，尽量减少隧道开挖引起的地层沉降和围岩变形，采用FLAC3D对4种施工工法全断面法、短台阶法、单侧壁导坑法和双侧壁导坑法进行模拟，分析了4种工法下地表沉降、隧道围岩周边位移和塑性区的变化特点，选出一种技术可行、经济合理的施工工法，得出一些有意义的结论。

Construction project optimizing of soft rock and shallow buried tunnel

Recently many problems such as surrounding rock collapse, large-area settlement of ground surface etc have happened during soft rock and shallow buried tunnel construction of express highway. The stratum condition of a shallow buried zone of Guangfu Tunnel is very complex. The section is large and the lithology is weak. The action of conformation has much influence on the shallow buried zone. And its top length is very thin. It is very easy to cause cave-in collapse and fall of ground. In order to ensure the construction safety of shallow buried zone tunnels and reduce the stratum settlement and surrounding rock deformation caused by the excavation of tunnels, four construction projects are simulated by FLAC3D as much full section method, shot shoulder method, unilateral pilot tunnel method and double pilot tunnel method. The variation feature of ground surface settlement, surrounding rock circumjacent displacement and plastic zone during the four excavation projects are analyzed. These four construction projects are computed with finite element method. Some valuable conclusions are drawn: (1) the double pilot tunnel method may produce fewer vertical displacements and horizontal convergence and its stabilization is better. (2) the plastic zone radius for double pilot tunnel method is least. (3) it is the most reasonable that double pilot tunnel method is adopted in the shallow buried zone of Guangfu Tunne1.