Research On Soil Deformation Caused By Shield Construction In Gas-bearing Stratum

In the process of underground space construction,the shield method is currently the most widely used construction method.Shield construction will inevitably encounter a gas-bearing soil layer.The shallow gas in the gas-bearing soil layer will have a huge impact and harm on the construction process and the construction personnel.At the same time,it will also cause greater disturbance to the surrounding soil,causing soil Body deformation.In this paper,theoretical calculation method,actual measurement analysis method and numerical simulation method are used to study the soil deformation caused by shield construction in gas-bearing formations,and the formula for calculating soil deformation in shield construction in gas-bearing formations after deflation is put forward.The specific research content and innovative work of the "disturbance" effect and the phenomenon of "intermediate pressure zone"are as follows:After summarizing the soil types of soil layers in various regions of our country,most of the shallow gas pressure,burial depth and gas composition are found to be mainly CH4 gas produced by the decomposition of organic matter,and the causes are slightly different.Analyzing existing disaster cases,expounding the engineering impact of shallow gas in the gas-bearing soil,the control of gas release,and the change of matrix suction;at the same time,the gas-bearing soil is a special unsaturated soil with shear strength and soil mass.Deformation is affected by the suction of the matrix;the uncontrolled or controlled release of shallow gas will cause different degrees of disturbance to the surrounding soil,and the engineering solution is mainly based on the controlled release in advance.The soil deformation after deflation is equivalent to local uniform settlement,and construction factors such as soil squeezing effect,soil softening,grouting pressure and soil loss are considered,and the soil caused by shield construction in gas-bearing strata is proposed for the first time Deformation theory calculation formula;research shows that:the theoretical calculation results are more consistent with the measured data,and can better reflect the characteristics of surface deformation caused by shield tunneling in gas-bearing formations;through comparison and analysis with the surface deformation characteristics of saturated soil layers,it can be known that due to The matrix suction caused by the residual gas in the gas-bearing strata soil increases the uplift and deformation of the soil in front of the shield by about 30%compared to the saturated soil layer,and the settlement and deformation of the soil behind the shield tail increases by about 20%compared to the saturated soil layer;when the gas re-accumulation is serious Or when the gas-bearing layer is thicker,the friction of the gas-bearing soil in front of the shield excavation is relatively large.In the theoretical calculation and analysis,the cutter head thrust correction coefficient or the interface friction angle can be appropriately increased.Relying on the Tangqing section of Hangzhou Metro Line 7 project,continuous surface deformation monitoring was carried out on double-line shield tunneling in gas-bearing strata,and the law of surface settlement caused by double-line shield tunneling in gas-bearing strata was obtained.The analysis showed that:gas-bearing strata The impact range of the ground settlement caused by stratum shield tunneling is within 8m of the tunnel axis,and the ground settlement becomes stable after 25 days after the shield passes through;the average settlement of the leading line of the shield is greater than about 44%of the trailing line;the shield is tunneling in gas-bearing formations At the same time,there are "three disturbances",the formation of exhaust gas destroys the soil structure as "one disturbance",the advancement of the advance line is the "second disturbance",and the advancement of the subsequent line is the"third disturbance";at the same time,there is an "intermediate pressure zone" in the soil."As a result,the soil body is not exhausted completely and there is matrix suction,so that the settlement caused by the advance line shield tunneling is greater than the back line;the ground settlement and soil loss rate of the shield advance line in the gas-bearing formation are both greater than the back line,and the soft soil area The laws are different,and the settlement trough of the trailing tunnel is shallower than the trailing tunnel;FLAC3D6.0 software is used to simulate the soil deformation caused by shield tunneling in gas-bearing strata,and the results obtained are compared and analyzed with the measured data.Figure[54]Table[19]Reference[105]...