*3.2. Comparison of the Present Model with the Laboratory Experiments and Fem Results for Combined Waves and Current Loading*

It is necessary to verify the performance of the integration model including both fluid and soil models under the circumstance of complex nature loading. There are numerous laboratory experiments related to the seabed response around the marine structures to date. However, it is quite limited in terms of the experimental data available for the case of immersed tunnel. Thus, the verifications of the integration model are carried out by comparison with the laboratory experiments and the FEM (Finite Element Method) results from DIANA-SWANDYNE II [52] for the seabed without the structure instead in this section. Qi and Gao [38] conducted a series of flume tests considering wave and wave combined currents as dynamic loading, respectively.

**Figure 5.** Comparison of vertical distribution of maximum oscillatory pore pressure, effective normal stress and shear stress with the analytical solution [7].

The first validation of this section is compared to the laboratory experiments conducted under wave loading only [38]. The input data for the first validation are: wave height *H* = 0.12 m, water depth *d* = 0.5 m, wave period *T* = 1.4 s, seabed thickness *h* = 1.2 m, degree of saturation *S<sup>r</sup>* = 1.0, shear modulus *G* = 10<sup>7</sup> N/m<sup>2</sup> , Poisson's ratio *<sup>ν</sup><sup>s</sup>* <sup>=</sup> 0.3, permeability *<sup>K</sup><sup>s</sup>* <sup>=</sup> 1.88 <sup>×</sup> <sup>10</sup>−<sup>4</sup> m/s. Figure <sup>6</sup> depicts the wave patterns with corresponding dynamic pore water pressure of the seabed, which are predicted by the present model and obtained from the experiment and FEM model separately. It can be seen that the result obtained from both the wave model and seabed model are in good agreement with the test data, which indicate that the present model is capable for simulating the wave motion in the fluid domain as well as the corresponding soil response of a sandy seabed.

**Figure 6.** *Cont.*

(**b**) Wave-induced pore pressure in seabed (*ps*)

**Figure 6.** Validation of the (**a**) Water surface elevation (*η*) and (**b**) Wave-induced pore pressure in seabed (*ps*) under wave loading at *z* = −0.1 m against the experimental data (which was from [38]) and FEM result data (caculated from DIANA-SWANDYNE II [52]).

The second validation in this section is to compare with the previous laboratory experiments conducted by Qi and Gao [38]. Unlike the previous case, this test simulates the seabed dynamic response under wave and current, which are generated synchronously. The following current with velocity of 0.05 m/s is adopted. The wave parameters and the soil properties are the same as above. As shown in Figure 7, the fluid pattern tracked by the fluid model matches well with the experiment data, while the pore water pressure simulated by the present model in correspondence with that obtained from the experiment and the FEM model. Thus, the current model performs well for simulating a more realistic marine dynamic elastic behaviour including both the fluid and soil parts.

**Figure 7.** *Cont.*

(**b**) Wave-induced pore pressure in seabed (*ps*)

**Figure 7.** Validation of the (**a**) Water surface elevation (*η*) and (**b**) Wave-induced pore pressure in seabed (*ps*) under wave combined current loading at *z* = −0.1 m against the experimental data (which was from [38]) and FEM result (calculated from DIANA-SWANDYNE II [52]).
