Shield To Promote Long-distance Super-close Neighbors Tunnel

Shield tunneling is more and more popular during the construction of urban subway engineering. Generally tunnels are under city center so construction is restricted due to serried buildings; narrow site space; complex geotechnical condition; dense underground networks and busy traffic. The conditions of close-spaced double tunnels or multi-tunnels are frequently met in processing subway engineering in cities, so sometimes civil works must be done close to the existing tunnels with complex mechanics behavior. It means that negative influence to the existing tunnels may occur. One of the most difficult problems urgently needed to be resolved at present is how to protect the existing long tunnels and other linear underground structures close to shield tunneling sites.According to the practical study in the project between Sanyuanqiao and Liangmahe running shield tunnels of Beijing No.10 subway, this paper has made an overall analytical study on influence done by new nearby-neighbor tunnel construction with shield driven method to the existing shield tunnel. Theoretical analysis, a 3D numerical model analysis and a large amount of site monitoring data are introduced to research the problem by obtaining data about horizontal convergence; stress change of segments; flexural torque of segments; axis force of cross shaped steel shotcrete of the existing tunnel and development of plastic zone between the two tunnels during driving the new shield tunnel. Based upon the analysis of relation in several index during the driving; clear distance and relative location of two nearby-neighbor tunnels; the influence regulation to the existing tunnel during new tunnel driving were drawn. The results of this article are state below: 1) The law of the existing tunnel be affected during shield driving and the changing law of the clear distance. 2) Range of influence before shield reached and after through. 3) Sensitivity of monitoring indexes to the shield driving. 4) Development law of plastic zone. 5) The "lagging effect" of the monitoring index to the shield driving. 6) Effectiveness of the strengthening measures in the construction. It resolved the problem that the shield drive across the long-distance nearby-neighbor tunnels, and can be regarded as a reference in other similar projects.