Abstract: Current theoretical studies on ground settlement induced by small curvature shield excavation generally consider the foundation as linear elastic bodies, neglecting the rheological behavior of soil. Therefore, the time-dependent settlement changes of shield excavation along curved path cannot be accurately predicted. A mechanical model for small curvature tunneling in a Boltzmann viscoelastic foundation was established. Time domain parameters of the viscoelastic ground were obtained through Laplace transforms of the Poisson’s ratio and shear modulus for the linear elastic ground parameters. Then, the solutions for ground loss and Mindlin displacement were converted by positive and inverse Laplace transforms. During small curvature shield construction in the viscoelastic ground, a settlement solution was derived that accounts for the combined effects of over-excavated ground loss, shield tail ground loss, cutterhead face thrust imbalance, shield shell friction imbalance and slurry pressure at the shield tail. Finally, field measurements and three-dimensional numerical simulation results are compared with the analytical solution to verify its relative accuracy. In addition, the parameters of tunnel curvature radius, shield cutterhead face radius and viscoelastic ground shear modulus ratio are analyzed. The analysis results show that the transverse surface settlement inside and outside the small curvature tunnel is asymmetrically distributed, with the peak settlement shifting inward. The settlement trough curve shifts downward and the settlement volume increases with time. A smaller tunnel curvature radius has a more significant effect on ground settlement compared to a larger tunnel radius curvature with equal changes. Reduction in tunnel curvature radius and viscoelastic ground shear modulus ratio, along with growth in cutterhead face radius and over-excavated value, result in the increase in transverse surface settlement at the shield tail, as well as the increase in uplift and settlement of the longitudinal surface both before and behind the cutterhead face.

Key words: viscoelastic ground, small curvature tunnel, over-excavated value, ground settlement, Laplace transform