针对某隧道排烟通道超近距(4.44 m)上跨已施作主洞结构,现场提出了一种微差爆破施工技术,采用有限元数值计算方法,探究上部排烟通道爆破施工后,下部主洞初期支护结构第一主应力、振动速度、位移的变化特征,定量评价近接隧道的安全状态。结果表明:纵向排烟道全断面爆破后,主洞初期支护结构最危险点位于纵向排烟道爆破掌子面正下方拱顶位置,控制性节点的X、Y、Z方向振速峰值均小于规范值20 cm/s、位移值处于3.63 mm以内;衬砌结构应力及变形曲线在200~300 ms内形成峰值,随着时间增加呈震荡衰减趋势,拱顶局部形成拉应力集中状态,结构整体风险可控。现场采用微差爆破技术施工后,排烟通道顺利上跨通过主洞结构,相交位置初支拱顶处由于个别锚杆弯撬出现局部初支掉块现象,整体受力较为安全。现场监测结果与数值计算相互吻合,证明该微差爆破施工技术的可靠性,研究成果可为类似工程提供参考。

A micro difference blasting construction technique was employed on-site to investigate the changes in the first principal stress, vibration velocity, and displacement of the initial support structure of the lower main tunnel after the blasting construction of the upper smoke exhaust channel, in response to the construction of the main tunnel structure at a close range (4.44 m). The finite element numerical calculation method was used to quantitatively assess the safety of the adjacent tunnel. The results show that: After the full section blasting of the longitudinal exhaust duct, the most dangerous point of the initial support structure of the main tunnel is located at the arch position directly below the blasting face of the longitudinal exhaust duct. The peak vibration velocities in the X, Y, and Z directions of the control nodes are all less than the standard value of 20 cm/s, and the displacement value is within 3.63 mm; The stress and deformation curves of the lining structure peak within 200~300 ms and subsequently exhibit oscillatory attenuation over time. The local tensile stress concentration state is formed at the arch crown, and the overall risk of the structure is controllable. After using the micro difference blasting technology for construction on site, the smoke exhaust channel smoothly crossed through the main tunnel structure. At the intersection of the initial support arch crown, there was a local phenomenon of initial support falling off due to individual anchor rod bending and prying, and the overall stress was relatively safe. The on-site monitoring results are consistent with the numerical calculations, proving the reasonable reliability of the micro difference blasting construction technology. The research results can provide reference for similar projects.