页岩气地层隧道施工灾害分析与防控

Analysis and Control of Construction Risks of Tunnels in Shale Gas Stratum

页岩气赋存地层地质条件复杂,且伴有高浓毒气、高瓦斯等。文章以湖南龙永高速公路红岩溪隧道工程为背景,介绍了该隧道内涌出气体的试验检测结果,并对其成分和来源进行了分析。结果表明,区别于通常的高瓦斯隧道,红岩溪隧道涌出气体存在高浓度的CO毒气和刺鼻的油气。通过气体碳同位素检测、岩样及含油迹灰岩有机地球化学分析和饱和烃色谱色质分析,判识红岩溪隧道地层中见到的天然气及渗漏和溢出的轻质油,其成因类型属低熟煤型油气,主要油气来自附近的煤系地层在低熟热演化阶段所形成。同时,探讨了页岩气地层隧道有害气体产生机理及其地质构造成因,根据区域地质分析,下伏煤系地层是隧道有害气体的来源之一,同时蕴含在下寒武统牛蹄塘组泥页岩中的页岩气,可能部分通过地质运动产生的裂隙涌入隧道。根据上述特点,提出了一些相应的灾害防控措施,包括衬砌加强、超前钻孔勘探、围岩注浆封堵、混合式通风及有害气体负压抽放等,可有效降低页岩气地层隧道施工中有害气体危害。此外,加强页岩气地层隧道弃碴的处理,防止其引发地下水污染、人员中毒或其他次生地质灾害。由于页岩气地层地质条件的复杂性,隧道施工与运营期间有害气体的扩散规律有待进一步的深入研究。

The geological conditions of shale gas stratum are complex,accompanied by high concentration of toxic gas and gas.With the continuous development of transportation infrastructure in Western China,more and more highway tunnels will encounter construction difficulties while tunnelling being in shale gas stratum.Based on the Hongyanxi tunnel on Longshan-Yongshun Highway in Hu’nan province,this paper introduces the test results of the gas emission in the tunnel,and the components and sources are analyzed.The results show that,unlike the usual high gas tunnel,there is a high concentration of CO gas and pungent oil gas in the the Hongyanxi tunnel.By the carbon isotope detection,organic geochemical analysis of oil-bearing limestone sample and qualitative saturated hydrocarbon chromatography,the light oil and natural gas are identified in the stratum of Hongyanxi tunnel,the genetic type belongs to the low mature coal type oil and gas,the main oil and gas are formed in the low thermal evolution stage of the coal formation.At the same time,the harmful gas generation mechanism and geological structure are explored in the shale gas tunnel.According to the analysis of the regional geology,the underlying coal formation is one of the sources of the tunnel harmful gases,and the gas contained in the shale of lower Cambrian Niutitang Formation may partly flow into the tunnel through cracks generated by geological movement.According to the above characteristics,some corresponding disaster prevention and control measures are put forward,including lining reinforcement,advanced borehole exploration,surrounding rock grouting and plugging,mixed ventilation and negative pressure drainage of harmful gas ctc.,which can effectively reduce harmful gas hazards during tunnel construction in shale gas formations.In addition,the treatment of waste residue in the shale gas formation tunnel is strengthened to prevent it from causing groundwater pollution,personnel poisoning or other secondary geological disasters.Because of the complexity of the geological conditions of shale gas stratum,the law of the diffusion of harmful gases during the tunnel construction and operation needs further research.