Safety Measures and Early Warning Analysis of Tunnel Crossing Existing Section

The crossing between the new subway and the existing subway line is a high-risk working condition. When the new tunnel crosses the existing tunnel in a short distance, the stress state of the existing tunnel structure will inevitably change and the structure will be deformed. Therefore, it is very necessary to formulate necessary safety measures for the crossing existing section. The relevant safety guarantee experience of the Nanjing Metro Line under construction going up and down through the existing operation line was summarized. In the up-crossing condition, take the guarantee measures to strengthen the external conditions, internal conditions and emergency response. At the same time, combined with the numerical analysis, it is concluded that MJS portal reinforcement has an obvious protective effect on the existing tunnel; in the under-crossing condition, the supporting measures of strengthening the stiffness inside and outside the existing tunnel, configuring the test section and operation cooperation were taken. Combined with the numerical analysis, it is found that the circumferential + longitudinal reinforcement in the existing tunnel has a significant protective effect on the existing tunnel, and the change rate of settlement and horizontal displacement of the existing tunnel is the largest within the range of 20 m from the heading face. Finally, based on the existing interval warning situations in engineering practice, the relevant reasons were analyzed and warnings and references were provided for similar projects.