关键词: 隧道工程；原位扩建；二次扰动；应力演化；变化特征；敏感性分析

Abstract: In order to evaluate the stress disturbance degree and redistribution characteristics of the expansion and excavation of existing tunnels， taking the in-situ expansion project of the Nanling single-track railway tunnel as the research background， based on the classical elastic-plastic theory， and combined with the Mohr-Coulomb yield criterion， the calculation formulas of the surrounding rock diameter and circumferential stress change during the expansion process were deduced， and the influences of different formation conditions， initial stress， and equal-circle calculation methods on stress change were analyzed. The results showed that the second excavation causes the radial stress to decrease in varying degrees compared with that before the expansion， and the circumferential stress first decreases and then increases， and finally remains in the original stress state; the surrounding rock stress distribution state is closely related to the surrounding rock conditions， initial stress， equal-circle calculation methods， and the simplified calculation method of the equal-circle calculation of the sum of 1/4 height and span has good applicability to the calculation of the stress change of the surrounding rocks for the in-situ expansion of a single-line tunnel. The on-site measurement has verified the accuracy of the calculation formula of stress change， and provided a theoretical basis for the design of the excavation scheme of expansion tunnels and the optimization of the support parameters.

Key words: tunnel engineering; in-situ expansion; second disturbance; stress evolution; change characteristics; sensitivity analysis