Establishment of uniform ground movement model for shield tunnels

Ground movement pattern of shield tunnels was investigated.It was firstly put forward that the direction of ground movement was conditioned by soil types,and the novel parameter “movement focus” moved between the center and bottom of tunnel.Ground loss model of two tangent circles was adopted to establish a uniform ground movement model for shield tunnels by introducing the coordinate parameter of movement focus.This novel model included Park pattern and Loganathan pattern.Smax was the maximum surface settlement above the tunnel centerline induced by ground loss.Assuming that soil was undrained,the general calculation formulas for Smax,upper limit bounds and low limit bounds were deduced by use of the virtual image method.It was shown by theoretical analysis that Smax was always in the range of upper and lower limit bounds no matter what the soil type was.By comparing theoretical values with measured values from twenty-seven actual tunnels and with Peck values respectively,it was shown that:(1) twenty-one actual values were in the range of upper and lower limit bounds,six actual values were beyond but close to the bounds,with difference generally within 10%;(2) values of Smax calculated by Peck formula were also in the range of upper and lower limit bounds,while only one value was a bit larger.The above comparison evaluated the validity of the present calculation method.It would be applicable in pipe-jacking construction.