Stability analysis of deep and large vertical shaft excavation by raise boring machine method through upper soft and lower hard strata

In the deep and large vertical shaft excavation project, the composite stratum poses a great challenge to the stability of the vertical shaft surrounding rock, especially the upper soft and lower hard stratum. In this paper, a tunnel ventilation shaft is taken as the engineering background, and ABAQUS finite element software is used to establish a three-dimensional numerical model of the deep and large shaft crossing the upper soft and lower hard rock layers, and analyze the radial displacement and stress evolution characteristics of the surrounding rock. Subsequently, the effects of soft and hard rock stiffness ratios and construction stages on the stability of the surrounding rock were investigated by parametric analysis. The results show that the radial displacement and stress of the surrounding rock in homogeneous rock layers increase linearly with depth. However, the radial displacement and stress in the surrounding rock near the soft-hard rock interface decrease sharply with depth. In contrast, the influence of the soft and hard rock interface on the stability of the surrounding rock was most significant during the reverse and forward drilling stages. As the difference between soft and hard rock stiffness increases, the displacement attenuation near the soft and hard rock interface is more significant, and the threat to the stability of the surrounding rock is greater. These findings can provide a reference for deformation control and support optimization of deep and large vertical shafts under complex geological conditions.