Theoretical research on soil deformation caused by shield construction in gas-bearing stratum

When a shield tunnel passes through a gas-bearing formation, the presence of shallow gas will affect the normal construction of the subway. Relying on an actual project of a shield tunneling through gas-bearing strata, a theoretical calculation formula for soil deformation caused by shield construction in gas-bearing formations was proposed for the first time by equalizing the soil deformation after deflation to the local uniform settlement and considering construction factors including soil squeezing effect, soil softening, grouting pressure and soil loss. The research shows that the theoretical calculation results are in good agreement with the measured data, and can better reflect the characteristics of surface deformation caused by shield tunneling in gas-bearing formations. Comparison with the surface deformation characteristics of saturated soil layers indicates that the matrix suction in the gas-bearing formations caused by the residual gas respectively increases the uplift deformation of the soil in front of the shield and the settlement deformation behind the shield tail by about 30% and 20%. When the gas-bearing layer is thick, the air-bearing soil friction 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. © 2021, Science Press. All right reserved.