<p>The stability of surrounding rock in spiral tunnels is difficult to control because the orientation of the principal in-situ stress changes continuously relative to the tunnel axis. Although straight tunnels under fixed principal stress orientations have been extensively studied, stress disturbances associated with spiral geometries remain poorly quantified. This study investigates the geomechanical response of the Laoyingpan No. 1 dual-spiral tunnel in China by integrating in-situ stress measurements, multivariate regression-based inversion, and three-dimensional numerical simulations. A tensor-based Stress Disturbance Index (SDI) is proposed to quantify changes in both the magnitude and direction of the in-situ stress field. The results show that excavation-induced disturbance follows a three-stage evolution and is concentrated within a core zone extending approximately 0.5 tunnel diameters ahead of and behind the excavation face. Directional disturbance dominates before the face reaches a monitoring section, whereas changes in stress magnitude dominate after face passage and during the subsequent steady stage. A distinct double-peak disturbance pattern occurs at the haunch because of secondary disturbance caused by bench excavation. The critical stress ratio and displacement asymmetry both increase with the intersection angle between the in-situ stress direction and the tunnel axis. These findings clarify the dynamic stress-adjustment mechanism in spiral tunnels and provide a quantitative basis for optimizing asymmetric support under complex stress conditions.</p>