Abstract: Taking the in-situ expansion project of the Nanling Railway Tunnel as the engineering background， a vibrating wire borehole stress gauge was used to monitor the circumferential stress changes in the surrounding rock during the expansion of the tunnel. A three-dimensional finite element model of the expansion construction process at the intersection of the main tunnel and the shaft was established， after verifying the accuracy of the model by comparing the monitoring data with the model results， the change law of surrounding rock deformation and stress was studied when the full-face method was adopted for expansion. On this basis， the influence of expansion method and cyclic footage on expansion stability was analyzed. The results show that during the expansion， the circumferential stress of the surrounding rock at the arch toe and side wall of the main tunnel at the intersection shows stress release， and the shaft destroys the arching effect of the main tunnel; compared with the non-intersection points of the shaft and the main tunnel， the horizontal displacement of the tunnel increases by 47.5% after the expansion， and the vertical displacement of the tunnel increases by 29.3%. The stress of the surrounding rock of the vault changes from compressive stress to tensile stress; the second disturbance degree of surrounding rock is lower by using full-face method， and the safety of expansion can be effectively improved by reducing the cycle footage.

Key words: tunnel in-situ extension; surrounding rock stress monitoring; numerical simulation; expansion method; cyclic footage