基于数值模拟的黄土地区南山堡隧道进洞支护方案优化

Optimization of Tunnel Entry Support Scheme of Nanshanbu Tunnel in Loess Area Based on Numerical Simulation

黄土地区南山堡隧道穿越第四系上更新统砂质黄土,隧洞埋深浅、土层结构疏松和孔隙度大等特性,对隧道进洞安全构成较大危害。利用有限元软件,建立三维数值模型,对比了两种不同超前支护方案下隧道进洞的围岩变形和地表沉降。基于此,进一步对隧道安全进洞措施优化进行分析。研究表明,隧道施工采用三台阶临时横撑法、双层超前注浆小导管加管棚能显著控制隧道变形,保证隧道进洞施工安全。同时,掌子面加固措施采用6 m长25玻璃纤维砂浆锚杆、仰坡防护后,隧道拱顶沉降峰值约为8 mm,隧道水平位移峰值约5 mm,地表沉降峰值约为6 mm,满足设计规范,隧道进洞施工更安全。优化后得出采取洞口超前大管棚、超前双层小导管、掌子面玻璃纤维砂浆锚杆加固、三台阶临时横撑法等的支护方案,为黄土地区隧道设计、施工提供经验。

The Nanshanbu Tunnel crosses the Quaternary upper Pleistocene sandy loess in loess area,with the characteristics of shallow buried depth,loose soil structure and large porosity,it poses a great harm to the safety of tunnel entry.In this paper,the three-dimensional numerical model is established by using the finite element software,and the surrounding rock deformation and surface settlement of tunnel entry under two different advance support schemes are compared.Based on this,the optimization of tunnel safety access measures is further analyzed.The research shows that the tunnel deformation can be significantly controlled and the safety of tunnel entry construction can be ensured by using the three-step temporary cross bracing method,double-layer advance grouting small conduit and pipe shed.Meanwhile,after taking 6 m long25 glass fiber mortar anchor bolt and front slope protection as the the reinforcement measures of the tunnel face,the peak settlement of tunnel vault is about 8 mm,the peak horizontal displacement of tunnel is about 5 mm,and the peak surface settlement is about 6 mm,which meets the design specifications and makes the tunnel entry construction safer.After optimization,it is concluded that taking the support schemes,such as advance large pipe shed at the entrance,advance double-layer small conduit,reinforcement of tunnel face with glass fiber mortar anchor bolt and three-step temporary cross bracing method,can provide experience for the tunnel design and construction in loess area.