Abstract:  In this paper, a case study is conducted on the Qiyueshan tunnel of the Moudao connecting line project on the LichuanWanzhou expressway. The conditions of the 26 karst caves exposed during tunnel construction are investigated, and the development scale, filling characteristics, waterbearing characteristics, development location, and geological origin of karst caves are analyzed. Furthermore, the influence of the superlarge karst cave on the tunnel surrounding rock deformation is studied using numerical simulation, and the treatment technologies of karst caves in different positions of the tunnel are discussed through case analysis.  The results reveal the following: (1) In exposed karst caves, the mediumscale one is the most common, followed by largescale one, and the smallscale and superlarge scale ones are the least common; the exposed karst caves are mostly dry with no or partial filling, and the development location mainly concentrates on the tunnel face. (2) The climate and hydrogeological conditions at the tunnel site are favorable for karst development, but due to the high tunnel elevation and groundwater level lower than the design level, no waterbearing karst cave is exposed. (3) The surrounding rock displacement at the junctions between the karst cave and tunnel is the largest, so the support should be strengthened. (4) The treatment techniques and principles of karst caves of various sizes and locations are developed and applied to engineering practice. The subsequent operation results validate the feasibility of the treatment methods. It is proposed that normalized advance detection, standardized treatment process, modular treatment technique, and targeted treatment scheme should be established for karst cave treatment.

Key words: karst tunnel, karst cave, development characteristics, deformation law, treatment techniques