Assessment and modification of traditional methods for ground displacements induced by shield tunneling

The issue of soil displacements caused by shield excavation is the hot topic in academic and engineering fields. Firstly, the traditional computation theories of soil vertical displacements are introduced. The ground surface settlements of 5 classical shield tunnels are calculated and analyzed. The analysis results show that: the fitting precision of Peck equation, Yoshikoshi method and Celestino method is higher, and the maximum settlements calculated by Loganathan & Poulos method are a little less than the measured data. The calculated results by Sagaseta method are mostly the same with those by Verruijt & Booker, while the maximum settlement is obviously small. The calculated results of Park method for shallow tunnel match well with the measured data. Secondly, based on cases of measured data of surface settlements, the modified fitting formula of width coefficient i_s of soil surface settlement trough is obtained. The formula is related to the tunnel radius R, axis depth h and soil conditions (internal friction angle φ of soil). The value of i_s is linear with R+h tan(45^°-φ/2). In addition, according to the statistical analyses of some cases of measured data of subsurface settlements, the modified fitting formula for width coefficient i_z of subsurface settlement trough is acquired. The formula for relationship between i_z/i_s and h_z/T is the logarithmic function (h_z is ground depth and T is thickness of overlying soil). The case analyses show the modified fitting formulae for the width coefficient of ground surface and subsurface trough agree with the measured data.