Abstract:

At present, the existing theoretical research on the seepage field around the subsea shield tunnel under the action of waves generally considered the lining as impermeable medium, and rarely studied the permeability of the tunnel lining, especially the influence of wave nonlinearity under the seabed slope terrain. Firstly, based on the dynamic boundary conditions of sloping seabed surface, the Biot’s consolidated pore water pressure response of free seabed under Stokes nonlinear wave is obtained. Secondly, the mirror image method is introduced to establish a governing equation of excess pore water pressure caused by the existence of tunnel, and the analytical solution of the equation is obtained by Fourier series expansion under the condition of continuous seepage between sand and lining. After that, the seepage response solution of the sand around the tunnel in the sloping seabed under the action of Stokes wave is obtained based on the superposition principle. Finally, the theoretical analytical solution is compared with the numerical results and the existing experimental results, and a good agreement is obtained. In addition, the influencing factors of wave sensitive parameters (wavelength, period and shape), seabed sensitive parameters (seabed permeability, shear modulus, saturation and slope) and tunnel sensitive parameters (lining thickness, permeability and buried depth) are analyzed. The results show that the excess pore water pressure outside the lining increases obviously with the increase of wave period and wavelength. As the water depth decreases along the seabed slope, the difference of wave pressure obtained by Airy wave and Stokes wave theory increases significantly within the applicable range (d/L＞0.125, where d is the water depth, and L is the wavelength), and the former will underestimate the excess pore water pressure around the tunnel. When the seabed permeability coefficient is large (k_s＞1×10⁻² m/s), the increase of wavelength and seabed saturation will increase the excess pore pressure outside the lining, while the increase of seabed shear modulus, seabed slope and tunnel buried depth will reduce the excess pore pressure outside the lining. Under the condition of inclined seabed with large slope angle, the excess pore pressure outside the tunnel lining shows an obvious asymmetric distribution. When the seabed permeability coefficient is small (k_s＜1×10⁻⁴ m/s), the excess pore water pressure around the tunnel is at a low level, and the influence of other sensitive parameters is not significant. When the permeability coefficient of tunnel lining is small (k_t＜1×10⁻⁶ m/s), the "blocking" effect of tunnel on the propagation of excess pore water pressure in sand is obvious, but when the permeability coefficient of lining is large (k_t＞1×10⁻⁴ m/s), and the excess pore water pressure in the sandy seabed around the tunnel is low. The influence of lining thickness on the distribution of excess pore water pressure outside the lining is not significant.

Key words: subsea shield tunnel, sloping seabed, Stokes wave, seepage pressure, mirror image method