大断面饱和黄土隧洞成洞条件研究

针对南水北调中线穿黄连接段大断面饱和黄土隧洞的成洞条件问题 ,应用岩土工程软件FINAL对几种可能的方案进行了施工仿真试验研究。研究结果表明 :①新奥法施工方案在该大断面高水头饱和黄土围岩中能够成洞 ;只需紧跟掌子面喷护 ,挂网 2 5cm加系统锚杆形成柔性支护圈即可维持围岩稳定 ;②双洞中心相距 2 .5倍洞径时应力与变形的相互影响小于 5 % ;③双洞合一的掏槽一次永久衬砌方案也可成洞 ,且施工技术要求最低 ,但洞周变形最大 (约 1 40mm) ;④双洞合一的预制混凝土超前压桩衬砌方案虽施工工艺复杂 ,但却能最大限度的限制围岩变形 (最大沉降小于 1 0mm) ,在重要建筑物底下穿过时 ,可能是首选方案。

Research on the tunneling methods in saturated loess

Three tunneling methods in the saturated loess for the project of water transferring from south to north of China are numerically tested and discussed with the introduced Austria software FINAL.The numercial results demonstrate:(1)Tunneling with NATM (CASE A) is possible and the 10 15 cm shotcrete immediately following the excavation is absolutely necessary ;(2)The interaction between two parallel tunneling caves with a distance of 2.5 times of tunnel diameter can be ignored ;(3)Instead of projecting concrete support to strengthen the surrounding loess of the tunnel,the traditional tunneling method(CASE B) in which the cast in site lining system is introduced to support the loess,is also possible for the local simple constructors,although the settelements of the tunnel crown reached 141 mm;(4)To reduce the tunnel settlements,another tunneling method(CASE C) with the precast lining system constructed before the tunnel excavation,is much better than CASE B with settlements of 8.5 mm, although the precast lining technics is much complex than CASE B.(5)All the feasible tunneling methods are based on the effective drainage of the water from the current level to the bottom of the tunnel.