含气地层盾构施工引起的土体变形理论研究

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

盾构隧道穿越含气地层时,浅层气的存在将会影响地铁的正常施工。为探究其影响,依托某盾构穿越含气地层的实际工程,将放气后的土体变形等效为局部均匀沉降,并考虑挤土效应、土体软化、注浆压力以及土体损失等施工因素,首次提出含气地层盾构施工引起的土体变形理论计算公式。研究表明:理论计算结果与实测数据较为吻合,能较好地反映含气地层盾构掘进引起的地表变形特征;通过与饱和土地层地表变形特征对比分析可知,由于含气地层土中残余气体引起的基质吸力,使盾构前方土体隆起变形比饱和土地层约增加30%,盾尾后方土体沉降变形比饱和土地层约增加20%;当气体回聚严重或含气层较厚时,盾构开挖面前方含气土摩擦较大,理论计算分析时可适当增加刀盘推力修正系数或者界面摩擦角。

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.