Abstract: Hidden caves have an important impact on the safety of the tunnel excavation. The FLAC3D software was used to investigate the influence of karst rock cavities with different diameters and distance to the tunnel crest on the rock mass surrounding the tunnel. The results show that the safe distance of the karst rock cavity to the tunnel from the groundwater intrusion is about 6 meters, and the deformation around the tunnel due to the rock cavity is mainly in the vertical displacement. When the distance between the cavity and the tunnel is greater than 2 to 3 times the radius of the karst cavity, the influence on the tunnel will be weakened. When the distance between the two increases by every 2 meters, the volume of the plastic zone φ decreases to approximately 15.3%~12.4%, while the volume of the plastic zone outside the boundary decreases approximately 8.5%~6.7%. After these statistical analyses, the linear relationship between the settlement and displacement of the tunnel crest and the size distribution of the karst rock cavity is obtained, which provides references for the design and construction of similar projects.

Key words: karst rock, tunnel, rock mass stability, numerical simulation