*6.3. Effects of Current*

In reality, the fluid circumstance above the seabed are quite complex, and need to considered in the wave–current interaction. The motion of the current is able to influence the wave propagation, which further affects the seabed liquefaction process. This section aims to investigate the relationship between seabed liquefaction and the current around the immersed tunnel. The seabed response under a second-order Stokes wave (*T* = 10 s, *H* = 4 m and *d* = 35 m) with a series of following currents (*U*<sup>0</sup> = 0.5, 1.0, 1.5 m/s) and opposing currents (*U*<sup>0</sup> = −0.5, −1.0, −1.5 m/s) are compared with the no current case. Other parameters used in this study are listed in Table 4.


**Table 4.** Parameters used in study of effects of current.

As seen in Figure 17, the maximum liquefied depth in seabed around the tunnel (*x* = 80 m) is 0.4 m, 0.6 m and 0.7 m when the current velocity *U*<sup>0</sup> takes on −1.5 m/s, 0 m/s and 1.5 m/s, which indicate the following current could deeper the liquefaction zone while the opposing current could decrease the liquefaction depth. Moreover, Figure 18 shows the liquefaction area around the immersed tunnel (when wave trough travels above the cross section *x* = 80 m) triggered by the wave combined different currents velocities. It can be concluded that not only the liquefied depth, but the liquefaction zone changes around the tunnel are also positively relative to the velocity of the current. Thus, oscillatory liquefaction is more likely to occur under the following current and the opposing current is able to decrease the potential of liquefaction.

**Figure 17.** The liquefaction conditions around the tunnel with different wave height.

**Figure 18.** Effect of currents *U*<sup>0</sup> on maximum liquefaction depth around the immersed tunnel.
