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

Impact of Advance Pilot Tunnel Excavation in High-stress Soft Rock Tunnels on the Main Tunnel:A Case Study of the Yulong Snow Mountain Tunnel Project

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,探明主洞与平导间最优间距。研究结果表明:主洞开挖过程中,当掌子面超过监测面3.63倍主洞宽度的距离后,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;主洞拱顶沉降值和仰拱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。

In order to investigate the impact of advance pilot tunnel excavation in high-stress soft rock tunneling projects on the main tunnel,this study leveraged the Yulong Snow Mountain Tunnel project.Utilizing long-term field monitoring data and employing a numerical analysis model based on the finite difference program FLAC3D,the study examined the influence of advance pilot tunnel excavation on the stress of surrounding rock,rock displacement,and the distribution of plastic zones in the main tunnel,and the optimal spacing between the main hole and the horizontal guide was determined.The research findings reveal 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 crown settlement,upper convergence,middle convergence,and lower convergence values at the monitoring section account for over 80%of the final deformation.After the deformation of the surrounding rock stabilizes,both upper and middle convergence values surpass the crown settlement.Advanced excavation of parallel pilot tunnels can effectively weaken the stress environment of the main tunnel.When the distance between the main tunnel and the parallel pilot tunnel is relatively large,the weakening in the surrounding rock stress is less pronounced.As the distance between them gradually decreases,the weakening in surrounding rock stress becomes increasingly significant.However,if the distance between the main tunnel and the parallel pilot tunnel is too small,the plastic zones generated by both excavations may intersect.Taking all factors into account,it is determined that the most optimal spacing between the main tunnel and the parallel pilot tunnel is 3.5 times the width of the parallel pilot tunnel.The crown settlement and invert uplift values of the main tunnel increase as the distance between the main tunnel and the parallel drifts decreases.The horizontal displacements of the left and right arch waists firstly decrease and then increase as the distance between the main tunnel and the parallel pilot tunnel decreases.