This paper investigates the ground deformation characteristics induced by mechanized shield twin tunnelling along curved alignments by adopting the nonlinear three-dimensional (3D) finite element method (FEM). The performance of the adopted FEM is demonstrated to be satisfactory by comparing the numerical analysis results with the field monitoring data in a typical case history and with the predicted results generated by a modified version of the Peck’s empirical Gaussian formula. It has been found that the tunnelling-induced transverse ground surface settlement troughs and the distributions of the subsurface horizontal and vertical ground displacements are mostly similar in both form and magnitude for the considered various radii of curvature of tunnel alignment including 50 m, 100 m, 150 m, 200 m, 250 m, 300 m, 400 m, and infinity (i.e., straight-line tunnel). Considering the variational characteristics of the ground deformations with the magnitude of the radius of curvature, the radius of curvature of 100 m can be regarded as a critical tunnel alignment radius of curvature controlling the transformation of the curved tunnelling-induced ground deformational behaviors. For the benefit of geotechnical engineers interested in curved tunnelling with a small radius of curvature, a discussion of the technologies for reducing the overexcavation and improving the accuracy of tunnel lining segment installation is also presented.

Surface effects are indispensable for crystalline materials when the characteristic size falls into nanoscale. In this paper, the size-dependent jump-in instability of an ultrathin film, omnipresent in nanoelectromechanical systems, is analyzed by incorporating the effects of surface energies. Based on a nonclassical thin plate theory including surface effects and the thermodynamic energy balance theorem, the jump-in instability mechanism of the film is established to determine the critical separation gap and contact length between the film and the substrate. We found that the dimensionless forms of these two mechanical properties depend on the thickness of the film. When the residual surface stress is ignored, the critical separation gap is affected by the surface elasticity, but the contact length is not. An aluminum film is considered as an illustrative example, for which the effect of residual surface stress is superior to that of surface elasticity.

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