Study on Influence of Stratum Expansion Force upon Stress State of Shield Segments

The expansive soil is prominently characterized by water swelling and dry shrinkage,and the swelling and shrinkage deformation is reversible over and over again. But the studies on shield tunnel in the similar strata were relatively fewer. For this reason in this paper,in combination with an actual example of shield tunnel on Chengdu Metro,the work conditions were classified according to the relationship between buried depth of shield tunnel and its diameter. And then through a single change of expansion force,a load-structure model was established by using shell element of finite element software, so as to calculate the internal force of every shield segment under different work conditions. By comparative analysis on shield segment internal force and safety factor,the influence of expansion force upon the stress state of shield segment was studied. The results of the study show that:( a) with the increasing of buried depth of the tunnel,the stratum expansion force is beneficial to the stress state of the shield segment;( b) the influence of stratum expansion force on shield segment can be reduced by adjusting route elevation,increasing buried depth of shield segment,grouting behind the segment and by other measures.