关键词: 轨道交通, 浅层天然气, 逆断层, 地下工程, 运移规律

Abstract: To avoid frequent outbursts of shallow natural gas in the reverse fault area, a case study of the Chengdu metro line 30 is conducted, and CH4 shortterm and longterm monitoring tests, CH4 recharge test, and gas chromatography test are employed to explore the characteristics of gas outburst, recharge, occurrence, and accumulation capacity of shallow gas in reverse fault areas. The results reveal the following: (1) The shortterm accumulation of shallow natural gas in the active reverse fault area is strong, outburst volume is large, and recharge speed is high, but the sustainability of the replenishment is poor. (2) In the broken zone of the static reverse fault, the shortterm accumulation of shallow natural gas is strong, outburst volume is large, recharge efficiency and sustainability are good, and longterm ventilation measures can effectively reduce the shortterm accumulation ability and shallow natural gas outbursts in this area. However, in the fractured zone, shallow natural gas has weak accumulation ability, small outburst volume, poor recharge efficiency and sustainability, and most of the shallow natural gas around the borehole can be discharged by longterm ventilation. (3) In the static reverse fault, shallow natural gas is continuously distributed in the broken zone and unevenly distributed in the form of air bags within the fracture zone. (4) Shallow natural gas mainly accumulates within 1~2 km around the reverse fault. With the increase in depth, the concentration of gas increases, whereas the ratio of methane to other hydrocarbon gases (C1/C2+) decreases.

Key words:  , rail transit, shallow natural gas, reverse faults, underground engineering, migration law