机械与爆破法下路基开挖对既有临近隧道的影响

Influence of Excavating Roadbed by Mechanical and Blasting Methods on Existing Adjacent Tunnel

路基开挖过程中如何保证既有隧道的安全稳定是高速公路改扩建工程的棘手问题,一直以来制约着改扩建项目的快速发展。以杭金衢高速樊村隧道扩建工程为研究背景,通过数值模拟分别研究了采用机械法和爆破法开挖路基对既有临近隧道支护结构的影响。结果表明:机械法开挖路基对既有隧道衬砌结构的影响较小,在衬砌结构整体刚度效应下,衬砌结构内力主要集中在拱顶、拱肩位置,而变形主要集中在左拱肩位置,伴随着卸载效应的增加,在开挖结束时衬砌结构左拱肩位置最大变形量会达到4.0 mm,而拱顶会承受最大内力,拱顶最大弯矩会达到34.3 kN·m;与之对应,在爆破开挖最不利工况下,既有隧道迎爆侧侧墙位置所受爆炸冲击波能量最大,该位置衬砌结构质点瞬时速度最大,在衬砌结构完整的情况下最大瞬时速度可以达到11.2 cm/s,虽未超过规范要求,但当衬砌结构存在裂缝时仍存在破坏的可能性,在施工过程中应多加注意监测迎爆侧侧墙稳定性;在土体开挖范围内,爆破施工振动效应对隧道衬砌结构的影响大于机械开挖的影响,但机械开挖进度较慢,尤其遇到坚硬岩石的时候很有可能会延误工期,因此有必要在机械开挖工法中穿插爆破开挖工法以提高施工进度。

How to ensure the safety and stability of existing tunnels during subgrade excavation is a thorny issue in expressway reconstruction and expansion projects,which has restricted the rapid development of reconstruction and expansion projects.Taking the Fancun tunnel expansion project on Hangzhou-Jinhua-Quzhou expressway as the research background,the influences of mechanical method and blasting method on the support structure of existing adjacent tunnel are studied by numerical simulation.The result shows that(1)The mechanical method has little influence on the lining structure of the existing tunnel during subgrade excavation.Under the effect of the overall stiffness of the lining structure,the internal force of the lining structure is mainly concentrated on the vault and shoulder,while the deformation is mainly concentrated on the left shoulder.With the increase of the unloading effect,the maximum deformation of the left shoulder of lining structure will reach 4.0 mm at the end of the excavation.The vault will bear the maximum internal force,and the maximum bending moment of the vault will reach 34.3 kN·m.(2)Correspondingly,under the most unfavorable condition of blasting method,the position of the side wall of the existing tunnel facing explosion receives the largest explosion shock wave energy,and the instantaneous velocity of the lining structure at this position is the largest.When the lining structure is complete,the maximum instantaneous speed reaches 11.2 cm/s.Although it does not exceed the requirements of the specification,there is still the possibility of damage to the lining structure when there are cracks.We should pay attention to monitor the stability of the side wall facing explosion during construction.(3)Within the scope of soil excavation,the vibration effect of blasting construction has a greater influence on the tunnel lining structure than that of mechanical excavation.However,the progress of mechanical excavation is slow,especially in case of hard rock,which is likely to delay the construction period.Therefore,it is necessary to insert blasting excavation method into mechanical excavation method to improve the construction progress.