The section of the first phase of Hangzhou Metro Line 4 from Zhejiang Chinese Medical University Station to Binsheng Road Station is located in the south of Qiantang River.A significant amount of harmful gases were discovered in shallow underground layer during preliminary and detailed geotechnical investigations.The main components of these harmful gases include CH4,H2S,SO2,and CO,with methane(CH4)being the dominant gas.Through this engineering case study,the mechanism of gas generation and storage,the depth of gas-bearing layers,distribution range,gas pressure distribution,and the variation pattern of gas pressure over time during release in this subway shield tunneling section were investigated and summarized.Additionally,a method for releasing shallow underground harmful gases were introduced,utilizing exploration drilling combined with the principle of cross hole layout.It has the characteristics of strong applicability(not limited by site and stratum conditions),convenient operation and good methane release effect in the exploration and release of harmful gases in the underground shallow layer of subway shield.The analysis revealed that the shallow harmful gases in this area are mainly distributed in muddy and silty clay interbedded with silty sand layer,belonging to the self-closed biogas gas-bearing layer,which has the characteristics of poor connectivity,small gas storage space,large difference in gas abundance and large difference in gas pressure.
shallow underground harmful gasoccurrence characteristics of harmful gasrelease of harmful gasHangzhou Metro Line 4characteristic analysis
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