Abstract: It is difficult to rationally and economically estimate the reinforcement range of the intersection between the urban metro shield tunnel and existing railway tunnel. As a result, an optimization design method based on the strength reduction coefficient method for Nalicun StationNahong Interchange Station tunnel on the Nanning Metro Line 4 crossing underneath existing Chalu Tunnel is proposed, and the effectiveness of the method is verified by monitoring data. The research results show that: (1) There are certain limitations in using the characteristic point mutation as the criterion for the actual tunnel construction safety, and the maximum reduction coefficient under the deformation control standard can be adopted as the comprehensive safety coefficient. (2) The reinforcement thickness coefficient and length coefficient have a power function relationship with the comprehensive safety coefficient of the railway tunnel system. (3) And the monitoring feedbacks show that the proposed reinforcement scheme can effectively control the settlement and deformation of existing railway tunnel. 

Key words: shield tunnel, undercross construction, existing railway tunnel, reinforcement range, strength reduction method