<p>The design and construction of expressways inevitably require dealing with some karst areas, which introduce various engineering challenges. This report presents detailed analysis of karst development around the Ehan expressway in southern China to study the factors influencing karst development. Karst development conditions in terms of lithology, geological structure, geomorphology, hydrology, climate, and biology were obtained through geological drilling and geophysical method. The results of this study indicate that the karst tunnels of the Ehan expressway have complex karst features at the surface and subsurface, and that the karst development in the Emeishan area is stronger than that in the Jinkouhe area. However, the distribution of karst caves and groundwater in these two regions are non-homogeneous, vertically and horizontally. In identical geological structures, different lithology leads to different karst development characteristics. Lithology and geological structure provide material basis and development space for karst development, respectively. The combination of soluble rock and insoluble rock causes varying degrees of karst development. Karst and groundwater development also vary with the erosion base level and burial depth. Moreover, climate and biological factors can promote karst development. Finally, countermeasures for karst tunnel construction were proposed based on the impact of karst features on tunnel construction and operation.</p>