Ta Study On The Numerical Simulation Of Tunneling Ventilation And The Risk Assessment Of Gas Safety In The Non-Coal Strata Gas Tunnels

In pace of the Traffic development in the west China, especially in the Southwest, the gas safety in tunneling has become a hot spot of construction problems in highway, railway,hydropower engineering. The gas tunnels include the coal-bearing strata gas tunnels and non-coal strata gas tunnels. The accidents in gas tunneling reported in the past often take place in the process of uncovering coal, particularly in the coal-bearing strata gas tunnels which have been studied for a long time. However, the problems in non-coal strata gas tunnel have existed for a period of time since Paotaishan tunnel was constructed. The gas that has the characteristic of distribution randomly in the non-coal strata makes people ignore its threat. A lot of accidents happened at home and abroad, because it has no effective way to judge the risk rating of gas safety in tunnels.This thesis studies the ventilation by high pressure in single-head excavation section and the properties of the non-coal strata gas tunnel, based on the Xuanzhenguan tunnel of Lanzhou-Chongqing Railway.The results of the research show that the sections in the non-coal strata gas tunnel can be divided into three categories:local enrichment section, low permeability section, permeation fluid section. This depends on the formation condition of the gas enrichment and the way of gas generation, with analysis of the monitoring data. Fuzzy comprehensive evaluation model is established with the improved AHP for the gas safety in the non-coal strata gas tunnel. The results of risk assessment are consistent with the actual working conditions. At the same time, the ventilation effect and pollutions in low gas sections are detected in the artificial way. And one analysis of ventilation and gas migration by CFD software FLUENT is completed in gas sections. The two results indicate that the ventilation by high pressure which have two high-power fans operating together can basically meet the relevant safety standards when the tunnel was heading in3500m longitudinal distance. Nevertheless, it spends long time to ventilation, inefficiency and hidden dangers still. According to the above points, some suggestions to improve the tunnel ventilation scheme are proposed and gas risk countermeasures also.