Analysis and calculation of reverse torque of earth pressure balance shield

Shield is a kind of underground construction machinery used to excavate soil tunnel with efficiency,environmental protection,safety and high quality,and it is employed widely in city metro construction in China.The origin driving of shield is one of the key techniques in shield construction.Through analyzing normal and origin driving shields,the mechanical model of shield driving in the two driving modes is established with reference to fundamental principles of soil mechanics.The calculation formula for resistance moment of the shield is presented,and the composition and effects of resistance moment of normal driving mode of shield are analyzed.It is discovered that in the normal driving mode,the resistance moment from the cave wall is strong enough to countervail the reverse torque resulted from the shield chisels’ cutting rock,and during the origin driving,protective measures should be taken in between shield cushion and its crust to prevent torsion.The formula has been adopted in some earth pressure balance(EPB) shield tunneling construction project with good results achieved.Conclusions can be referenced for the design and application of EPB shield.