The ocean waves exhibit obvious non-linearity with asymmetric distribution of wave crests and troughs, which could induce significantly different effect on the seabed compared to the commonly used linear wave theory. In this paper, a semi-analytical solution for a transversely isotropic and multilayered poroelastic seabed under non-linear ocean wave is proposed by virtue of the dual variable and position (DVP) method. The ocean wave and seabed are, respectively, modelled using second-order Stokes theory and Biot’s complete poroelastodynamic theory. Then the established governing equations are decoupled and solved via the powerful scalar potential functions. Making use of the DVP scheme, the layered solutions are finally gained by combining the boundary conditions of the seabed. The developed solutions are verified by comparing with existing solutions. The selected numerical examples are presented to investigate the effect of main parameters on the dynamic response of the seabed and evaluate the corresponding liquefaction potential. The results show that the anisotropic stiffness and permeability, degree of saturation and stratification have remarkable influence on the dynamic response and liquefaction behavior of the seabed. The present solution is a useful tool to estimate the stability of transversely isotropic and layered seabed sediment in the range of non-linear ocean wave.

In recent years, shield tunneling has shown many advantages with the development of underground rail traffic. Geological exploration plays a significant role in tunnel engineering, and detailed geological exploration results can guide the successful construction of a tunnel. This research relies on a super large-diameter shield tunnel construction, using microtremor exploration technology to collect data onsite. Combined with a comparative analysis of the borehole surveying, the reliability of microtremor exploration technology is verified. Moreover, the monitoring result of the impact of large-diameter slurry balanced shield construction on the surrounding environment is analyzed. The results show that microtremor exploration can obtain geological details that traditional detection methods cannot obtain, which can predict the possible local geology mutation in front of the tunnel in advance. The law of surface settlement curve conforms to the Peck formula. This can be divided into five stages: micro deformation, extrusion uplift, reciprocating uplift, detachment settlement, and consolidation settlement. The surface settlement on the eccentric loads side is more prominent. The maximum pressure outside the tunnel segment appears on the lower side of the monitoring section, approximately 0.41 MPa, which will increase with the grouting pressure and become stable in five days.

The undrained shear strength is an essential parameter in the foundation design of marine structures. Due to the complex marine environment and technical limitations, it is difficult and costly to obtain offshore samples. Piezocone penetration tests (CPTU) are relatively low-cost compared to drilling and sampling methods. Therefore, based on the soil behavior type index (I_c) derived from CPTU results, a model for estimating cone factors (N_kt, N_ke) is proposed to improve the accuracy of estimation of undrained shear strength. The result shows that the soil behavior type index (I_c) and cone factors take on a negatively correlated exponential relation. Incorporating a cone factor that varies with the soil behavior type index (I_c) significantly enhances the accuracy of undrained shear strength predictions compared to the conventional method of using a constant cone factor. This approach reduces the root mean square error (RMSE) for N_kt (N_ke) from 0.124 (0.126) MPa to 0.056 (0.06) MPa, and the mean absolute error (MAE) from 0.0154 (0.016) MPa to 0.0032 (0.0036) MPa. The method was validated at an additional location and the predictions were in high agreement with the results of the consolidated quick direct shear test. The developed method can serve as an effective tool used in the design of foundations of marine structures.