含气地层中气体释放对盾构隧道稳定性影响研究

Study of influence of gas entering tunnel on stability of shield tunnel in gassy soil layer

随着地下工程的建设日益增多,部分工程穿越含气地层,含气地层会对隧道的施工产生一定不良的影响。盾构在沼气地层掘进过程中,由于管片气密性不良造成沼气通过管片环缝进入隧道,引起管片的纵向变形。针对这一现象,建立管片环缝单点气体释放条件下的管片变形模型,并用数值模拟方法与理论结果进行对比验证。通过其变形公式,分析不同含气层厚度、不同初始气压条件对管片的变形及管片接缝张开量的影响,探讨管片损坏的地层条件。结果表明,对于含气层较薄(<1.5 m)、气体压力比较小(<150 kPa)的地层,隧道气密性不严导致气体泄漏进入隧道会导致管片下沉,但一般不会破坏管片的防水设施。当含气层厚度大或气体压力较大时,气体释放会引起比较大的管片变形,破坏管片的防水能力,导致地下水进入隧道,引起管片的进一步变形;地层扰动大时,地层土体随地下水进入隧道,会造成管片的严重损坏,以至于断裂。

As the construction of underground project grows increasingly,more and more tunnels will be constructed in gassy soil(soil layer containing high-pressure gas),and the gas in soil may bring bad influence for the stability of tunnel by shield method.When the shield machine is driving in the soil layer,the gas may enters into the tunnel through segment seam because of bad air-tightness,it will cause longitudinal deformation of segment.Aiming at this phenomenon,the purpose of this paper is to establish a segment deformation model under the condition that the gas enters into the tunnel through single point at the segment seam.For the purpose,firstly the stratum deformation caused by gas releasing was studied;the curve fitting method was used to obtain the relationship between stratum deformation curve and the maximum settlement value.Then the numerical simulation software FLAC3D was used to verify results gotten by theoretical deduction;Comparative results show that the numerical results and the theoretical results are basically consistent,so as to verify the availability of the theoretical formula.By segment deformation formula and deformation compatibility equation,the influence of different gas layer thicknesses and different initial gas pressures on the segment deformation and the open value of segment seam are analyzed;and the condition of soil layer causing the damages of segment is discussed.Results show that,with the increase of the thickness of gassy stratum or the original gas pressure,the bending moment of segments will increase;and the opening values of segment joints will become larger.For the stratum with thinner gas layer(<1.5 m) or lower gas pressure(<150 kPa),bad air-tightness will cause the gas leak and enter tunnel and bring the damage of segment;but normally will not destroy the waterproof facility of segment;however,for the stratum with large gas layer depth or higher gas pressure,that the gas leak will cause larger segment deformation and destroy the waterproof ability,and make underground water entering into the tunnel.When the deformation of segment becomes larger,the sand will flow into the tunnel with groundwater,so as to bring serious damage of segment.