Study on Prediction of Surface Deformation during Shield Construction of Subway in Loess Stratum

Research purposes: The Xi'an subway is the first subway built in loess stratum in China,and the loess has some special physical and mechanical properties such as collapsibility.The shield construction is one of the main methods for construction of subway tunnel,but there is a little research on prediction of the feature of surface deformation induced by shield construction.So it is urgent to do the study on prediction of the features of the surface deformation induced by shield construction in loess stratum for the purpose of offering some theoretical basis for working out the monitoring program for the surface deformation and determining the shield construction parameters to ensure the construction safety of the shield tunnel. Research conclusions: The comparative analysis of the theoretical forecast computation and the measured data on the surface deformation of one interval tunnel of Xi'an subway was made and the results showed:(1) The predicted surface deformation tendency and data calculated by the prognostic formula was basically consistent with the actual value.(2) During shield construction,the front additional pushing force could remain the the stability of the soil in front of the excavating surface and the big or small of the the front additional pushing force could influence the big or small of the ground vertical displacement.(3) During shield construction,there were lots of factors to influence the ground vertical displacement,but the big or small of the gap of the shield tail had the biggest influence on the ground vertical displacement.(4) During shield construction,the ground settlement decreased with the increase of the axial distance of the tunnel,and deformation above the the tunnel axial was the biggest.