Features of karst development and geotechnical effects in the Liaoshan Tunnel on the E-Han expressway

The Liaoshan tunnel on the E-Han expressway is located in a karst area of southwest China with frequent geological hazards. Based on the investigation of the geological environment in the karst area，this work clarified the characteristics of karst development in the tunnel site area，analyzed its law and controlling factors，and examined its effects on the site. The results show that the karst morphology in the tunnel site area is diverse，characterized by multiple scales，diversity，and dense development. The karst shows significant selectivity，directionality，layering，heterogeneity，and system coherence and other laws，in which stratigraphic lithology and its combination are the material basis，topographic features and geological structural characteristics are the dominant conditions，and hydrogeological conditions are the decisive factors. The engineering effects of karst development are mainly expressed in 3 aspects， the stability of the tunnel，karst gushing water inrush and effect of tunnel life cycle. The existence of bad karst geological bodies and karst water-rich spaces can easily induce stability problems such as large cave deformation and karst collapses at the bottom of the tunnel as well as local static karst water outbursts and lake water flood and mud flooding disasters，sometimes even affecting the stability and durability of the tunnel structure during the operation period.