Study of the Segment Internal Force during the Construction of Shield Tunnel

In the section of Beixinqiao-Yonghegong left line of Beijing metro line 5,three test sections with different geological conditions were chosen to study the segment internal force during the construction of shield tunnel.Results show that,during the construction of shield tunnel,the segment internal force has been constantly changing and adjusting from the local stability state of the segment structure to the eventual balance between the formation and the structure.When the segments are in the scope protected by the tail-board,the axial force of the segment is larger in the azimuth about 45° or the arch bottom.After the segment is out of the protection of the tail-board,the soil mass and the filling slurry will generate the function to the segment,which makes the segment internal force increase rapidly,and the maximum increase amplitude is around 30%～40%.This is one of the key moments for the safe single-layer lining of the assembling segments.Geological conditions have great influence on the axial force of the segment.The axial force of the segment is larger in silty soil layers,while the axial force of the segment is smaller in sand and gravel layers. The influence of the geological conditions on the bending moment of the segment is not obvious.The grouting has a direct impact on the internal force of the segment out of protection of the tail-board.Improving the grouting effect can make the segment stress uniform and increase the durability of the segment.