高地应力软岩隧道超前平行导洞开挖对主洞影响：以玉龙雪山隧道工程为例

为研究高地应力软岩隧道超前平行导洞开挖对主洞影响,依托玉龙雪山隧道工程,基于现场长期监测数据,结合有限差分程序FLAC3D建立数值分析模型,研究超前平导对主洞围岩应力、围岩位移和塑性区分布的影响,明确主洞与平导间最优间距。研究结果表明:主洞开挖过程中,当掌子面与监测面距离为3.63倍主洞洞宽时,监测面拱顶沉降、上收敛、中收敛和下收敛值占最终变形值的80%以上,围岩变形稳定后上收敛值和中收敛值均大于拱顶沉降；平导超前开挖可有效改善主洞围岩应力环境,主洞与平导间距较大时,围岩应力改善效果不佳,随着二者间距逐渐减小,围岩应力改善效果逐渐增强,但主洞与平导间距过小时,二者开挖产生的塑性区会贯通,综合考虑,确定主洞与导洞最优间距为3.5倍导洞宽度；主洞拱顶沉降值和拱底隆起值随着主洞与平导间距的减小而增大,左右拱腰水平位移值随着主洞与平导间距的减小先减小后增大,当二者间距由5.0D减小至3.0D时,拱顶沉降值和拱底隆起值分别从-0.598m和0.426m增加至-0.679m和0.514m。

Study on Influence of Advance Pilot Tunnel on soft rock tunnel

In order to study the influence of parallel pilot tunnel excavation on the main tunnel of high-ground stress soft rock tunnel, based on the long-term monitoring data and the finite difference program FLAC3D, a numerical simulation model was established to study the influence of parallel pilot tunnel excavation on the surrounding rock stress, displacement, and plastic zone distribution of the main tunnel, and the optimal spacing between the main hole and the horizontal guide is determined. The results show that during the excavation of the main tunnel when the distance between the tunnel face and the monitoring section is 3.63 times the width of the main tunnel, the vault settlement, upper horizontal convergence, middle horizontal convergence, and lower horizontal convergence of the monitoring section account for more than 80 % of the final deformation value. After the deformation of the surrounding rock is stable, the upper horizontal convergence value and the middle horizontal convergence value are greater than the vault settlement. The advanced excavation of the parallel pilot tunnel can effectively improve the mechanical environment around the main tunnel.? When the distance between the main tunnel and the parallel pilot tunnel is large, the improvement effect of the surrounding rock stress is not obvious. As the distance between the two tunnels gradually decreases, the improvement effect of the surrounding rock stress gradually increases. However, when the distance between the main tunnel and the parallel pilot tunnel is too small, the plastic zone generated by the excavation of the two tunnels will be connected. The vault settlement value and the arch bottom uplift value of the main tunnel increase with the decrease of the distance between the main tunnel and the parallel pilot tunnel, and the horizontal displacement value of the left and right arch waist decreases first and then increases with the decrease of the distance between the main tunnel and the parallel pilot tunnel. When the distance between the two tunnels decreases from 5.0D to 3.0D, the vault settlement value and the arch bottom uplift value increase from -0.598m and 0.426m to -0.679m and 0.514m respectively.