无中墙连拱隧道先行洞爆破振动响应特性与隔振方案比选研究

Blast vibration characteristics and its isolation scheme selection of existing tunnels in multi-arch tunnels without middle wall

无中墙连拱隧道取消中墙结构,先行洞与后行洞净距减小,如何在后行洞爆破开挖过程中保证先行洞的爆破振动安全极其重要。依托某高速公路隧道,通过现场爆破振动跟踪监测,分析了后行洞开挖过程中先行洞边墙二衬的爆破振动响应特性;基于二维(2D)-三维(3D)联合模拟方法,研究了先行洞纵、横断面质点峰值振速(PPV)分布规律,并回归分析了先行洞二衬PPV与拉应力的关系;比较分析了不同隔振方案下的振动控制效果,并从施作可行性、效率及成本等方面,推荐了适宜的隔振方案。结果表明:无中墙连拱隧道后行洞开挖时,先行洞迎爆侧拱肩至拱腰区域振动强度最大,且以水平径向振动为主,振速在已开挖方向衰减更快,计算所得先行洞二衬的爆破振动控制标准为24.54 cm/s;布设隔振层可有效保障先行洞的爆破振动安全,隔振材料推荐为板材式L-600聚乙烯闭孔泡沫,厚度和高度分别建议为5 cm,5 m,先行洞拱肩及拱腰减振幅度可达54.8%,63.5%;现场监测数据表明,采用推荐隔振方案后,先行洞二衬再无裂缝出现,且PPV均未超过安全允许振速。

In the blasting excavation of the following excavating tunnel,it is extremely important to ensure the blasting vibration safety of the existing excavated tunnel,as the traditional middle wall is cancelled in the new multi-arch tunnel and the neighborhood spacing between the following and existing tunnels is very small.In this study,the blasting vibration characteristics of the secondary linings of the excavated tunnel at the side wall are analyzed based on the on-site blasting vibration monitoring at a highway tunnel.Then,based on the inheriting of the explosion pressure simulated by the two-dimensional(2D)fine model into the three-dimensional(3D)real-scale model,a coupling simulation method for blasting dynamic response is established.The distribution laws of the peak particle velocity(PPV)at the longitudinal and cross sections of the excavated tunnel are studied respectively using the aforementioned simulation method.Moreover,the safety control standard of the blasting vibration is calculated according to the fitting relationship between the PPV and the maximum tensile stress of the secondary linings of the excavated tunnel.Finally,the vibration control effects of the excavated tunnel under different vibration isolation schemes are analyzed,and the suitable vibration isolation scheme is recommended considering of the construction feasibility,efficiency and cost,etc.The results indicate that the vibration velocity near the arch-waist and arch-shoulder at the blasting side of the existing tunnel is the largest during the excavation of the following excavating tunnel.Besides,the PPV is governed by the horizontal radial vibration,and it decays faster at the excavated direction than that at the opposite direction.The blasting vibration control standard of the secondary linings of the excavated tunnel is calculated as 24.54 cm/s.The vibration isolation layer can effectively ensure the blasting vibration safety of the excavated tunnel,and the vibration isolation material is recommended as the plate-type L-600 polyethylene closed-cell foam,whose appropriate thickness and height are respectively 5 cm and 5 m.By using the above vibration isolation scheme,the vibration reduction ratios of the arch-waist and arch-shoulder of the exiting tunnel can reach 54.8%and 63.5%.Furthermore,the measured PPVs all do not exceed the safety threshold,and no cracks are found at the secondary linings of the excavated tunnel.