Analysis on Anti-Buoyancy Caculation In Excavation of Big Cross-Section Shield Tunnel

Segments floating is a main problem often met in shield tunnel excavation.The reasons of shield tunnel segments floating are discussed first,including the buoyancy produced by water,grouts or slurry,the gap produced by shield shell,and the disturbance produced by excavation to overburden soil,etc.Then,the problem of resisting the segments floating of shield tunnel is analyzed.In the analyzing process,both the restriction force of neighboring segments on the floating segments(including the friction between segment rings and the shearing resistance of longitudinal bolts) and the compression effect of Remain-Force on overburden soil are taken into account,in the case that the general weight of overburden and segments self-weight is smaller than the buoyancy.The analysis result indicates that the problem of shield segments floating is concerned with the self-weight of segments,overburden,the buoyancy,and the characteristics of the segments.To control the segments floating of shield tunnel,the methods not only include improving the quality of covering soil,increasing the thickness of covering soil,but also include improving the mechanical characteristics of the segments,such as adding the number of longitudinal bolts,enlarging their diameters,increasing their fastening force,and setting shearing force bond,etc.