Research On The Effect Of Shallow Noxious Gases On Railway Tunnel In Northern Shaanxi Province

In recent years,more and more attention is paid to the problem of gas combustion or explosion in the tunnel construction when through non-coal(oil)formation.The Ordos Basin is an important sedimentary basin in China,with large amount of coal and oil and gas resources.At present,there are many railway and highway constructions,and the problem of gas combustion when the tunnel construction through non-coal(oil)formation has occurred.Based on the Mengxi to Huazhong railway project which is under construction,the harmful gas problems in the Jingbian to Hancheng tunnel of the Ordos basin are studied and discussed.Firstly,the concepts of coal mine,petroleum and railway system on shallow gas are integrated,and the concept of shallow harmful gas in non-coal(oil)strata is defined.Based on the study of the distribution and characteristics of the north Shaanxi province oil and gas fields and coalfields in Ordos Basin and the relationship between shallow harmful gas and the tunnel engineering is analyzed,the hazard level partition of shallow harmful gases on the tunnel engineering is divided qualitively.Then,the impact of shallow harmful gas on the tunnel engineering is analyzed quantitatively by the test of on-site hole and rock specimen test.The source,migration,accumulation and distribution pattern of harmful gases in the middle and shallow layers of the Ordos basin from the Jingbian to Hancheng sections of the Mengxi to Huazhong railway project in the north Shaanxi province are obtained.It is concluded that compared with the traditional coal-bed methane,the distribution of the harmful gases in the shallow coal layer in the non-coal(oil)strata is characterized by the random distribution,the free state,the small amount of reserves and the low pressure.At the same time,the classification standard of the shallow harmful gas tunnel is summarized.According to the characteristics of the harmful gas in the shallow coal layer of the non-coal(oil)strata,the pertinent design principles of the shallow gas tunnel are proposed.It is proved that the design principle of the tunnel is reasonable and the engineering measures are proper,which bring great economic benefits to the engineering construction.