Study on formation mechanism of gas tunnel in non-coal strata

Gases are common constituents of the underground environment, along with soils, rocks, and water. It is widely believed that gases in underground originate from the bacterial decomposition and thermal decomposition of organic and inorganic compounds, and geochemical reactions. Gases are usually widely dispersed in low concentrations, but under some geologic conditions are abundant. Gas can be a hazard to construction of underground civil works such as tunnels and underground chambers. Besides the gas tunnels in coal seam, there are a large number of tunnels with gas in non-coal strata in China, such as the Paotaishan Tunnel, Hongshiyan Tunnel, and Zengjiaping 2# Tunnel. These tunnels do not cross coal strata, but all encountered gas problems during construction. Due to lack of full understanding and thorough preparation, as well as the random non-uniform distribution of gas emission, the gas disasters in these tunnels are usually larger than the traditional ones. Study on the causes of formation has great scientific significance. This paper focuses on a variety of complete gas tunnels, summarized three types of gas tunnel in the non-coal strata, namely the structure-connected gas tunnel, including fracture, fault, and fold three subtypes according to the different geological structures; the second one is gas tunnel with metamorphic wall rock; the third is gas tunnel by composite forming causes.