浅埋弃土段大断面隧道施工力学行为研究

Mechanical behavior of the large section tunnel construction in a shallow spoil segment

以龙洞堡机场隧道为工程背景,对弃土段隧道大变形原因进行深入分析,提出相应的改进措施,使隧道顺利通过剩余弃土段。研究结果表明,隧道所处人工弃土段与经压密原生土体物理性质存在差异,小导管与袖阀管注浆无法在弃土层扩散,反而增加了覆土重度,增大了隧道上覆荷载;实践证明对剩余弃土段采取二重管双液注浆,其效果要明显优于上述两种注浆措施;掌子面预留核心土和掌子面锚杆有效控制了掌子面前方先行位移,剩余弃土段掌子面先行位移约占总位移的15%～18%,达到减少掌子面先行位移的目的;弃土段隧道开挖,上覆土体呈现出整体下沉趋势,通过拱脚注浆锁脚锚杆可以减少初期支护拱脚、边墙脚沉降和过大水平位移;通过数值计算分析表明弧形导坑法开挖时,安全系数最小值发生在隧道仰拱中部,其量值为3.36,初期支护安全系数均大于2.4,支护体系在施工阶段是安全的。

Considering the Longdongbao Airport Tunnel engineering background, the large deformation reason of spoil sections of the tunnel was analyzed. The corresponding measures for improvement and practical engineering use were put forward and the tunnel passed the remaining spoil segment. The results show that physical differences exist between the artificial spoil segment near the tunnel and the original adobe after compaction, and a small catheter with the Sleeve Valve Pipe cannot spread in the abandoned soil. The increasing casing severe increases the tunnel overlying load. The practical results prove that when the double pipe grouting is used in the remaining spoil segment, the effect is much better than the above two grouting measures. The tunnel face reserved core soil and tunnel face bolt can effectively control the first displacement ahead of the face, and the remaining spoil paragraph heading face first displacement accounts for about 15% to 18% of the total displacement to achieve the purpose of reducing the face first displacement. The spoil sections of the tunnel excavation shows a trend of overall sink. Using the arch grouting lock foot anchor pipe can reduce the initial support arch of the foot, the side skirting settlement and the excessive horizontal displacement. The numerical analysis of the arc drift method excavation shows that the minimum factor of safety in the tunnel occurs in the central part, and its value is 3.36. The initial support safety factor is greater than 2.4, and the support system is safe during the construction phase.