The expansion of transportation infrastructure into geologically complex mountainous regions of China has increased encounters with gas-bearing non-coal strata during tunnel construction. Unlike coal-measure gas systems, gas occurrences in carbonate, clastic, and metamorphic rocks present distinct challenges due to multi-source origins, structurally controlled accumulation, and abrupt outburst mechanisms. This review examines existing research to establish a conceptual framework for this hazard category. Analysis of gas sources, reservoir characteristics, and geological controls indicates that non-coal gas tunnels require theoretical approaches distinct from coal-gas methodologies. A genetic... More >