*5.1. New Anchor Structure Style* The numerical analysis shows that the excess pore water pressure appears outside of the

The numerical analysis shows that the excess pore water pressure appears outside of the anchor, while negative pore water pressure appears inside. According to the principle of effective stress, the soft clay structure on the external anchor wall is degraded followed by the degradation in strength. The uplift capacity of suction anchor gradually decreases with the development of excess pore water pressure. According to the distribution characteristics of the residual pore pressure, a perforated anchor is proposed based on the traditional suction anchor, as shown schematically in Figure 15. Perforation at the lower part of the anchor wall is helpful to reduce the accumulation of excess pore water pressure. The installation process of the suction anchor is divided into two stages. First, the suction anchor is installed by self-weight to around half the design depth, and then negative pressure is applied until the anchor reaches the final depth [37,38]. Perforation is located at the lower part of the suction anchor, and therefore, the new structure style will not influence the installation process. anchor, while negative pore water pressure appears inside. According to the principle of effective stress, the soft clay structure on the external anchor wall is degraded followed by the degradation in strength. The uplift capacity of suction anchor gradually decreases with the development of excess pore water pressure. According to the distribution characteristics of the residual pore pressure, a perforated anchor is proposed based on the traditional suction anchor, as shown schematically in Figure 15. Perforation at the lower part of the anchor wall is helpful to reduce the accumulation of excess pore water pressure. The installation process of the suction anchor is divided into two stages. First, the suction anchor is installed by self-weight to around half the design depth, and then negative pressure is applied until the anchor reaches the final depth [37,38]. Perforation is located at the lower part of the suction anchor, and therefore, the new structure style will not influence the installation process.

**Figure 15.** The perforated suction anchor **Figure 15.** The perforated suction anchor.

#### *5.2. Comparative Study of the Pore Water Pressure Distribution 5.2. Comparative Study of the Pore Water Pressure Distribution*

perforated anchor.

To investigate the effectiveness of the perforated suction anchor on reducing the development of excess pore water pressure, the distribution characteristics of residual pore pressure around the perforated anchor are analyzed, and a comparison with the traditional anchor is presented. The perforation height is 0.5m, and this is located at the lower part of the suction anchor (0.9 < *z/h* <1). To investigate the effectiveness of the perforated suction anchor on reducing the development of excess pore water pressure, the distribution characteristics of residual pore pressure around the perforated anchor are analyzed, and a comparison with the traditional anchor is presented. The perforation height is 0.5m, and this is located at the lower part of the suction anchor (0.9 < *z*/*h* <1).

Figure 16 shows a comparison of the residual pore pressure distributions between the traditional anchor and the perforated anchor. As shown in Figure 16, the accumulation of excess pore pressure outside of the perforated anchor is reduced remarkably, compared with the traditional structure. The excess pore water pressure around the perforated anchor is reduced by about 27.5%. Therefore, the perforated anchor can effectively reduce the accumulation of excess pore water pressure and increase the effective stress in the soil. In this paper, the perforation height and perforation size were not quantified according to the length ratio of suction anchor and the initial penetration depth, so further research is wanted.

(**a**) On the inside of the anchor. (**b**) On the outside of the anchor. **Figure 16.** Comparison of residual pore pressure distribution between the traditional anchor and the

traditional anchor and the perforated anchor. As shown in Figure 16, the accumulation of excess pore pressure outside of the perforated anchor is reduced remarkably, compared with the will not influence the installation process.

*5.2. Comparative Study of the Pore Water Pressure Distribution* 

(a) The front view (b) The three-dimensional view

**Figure 15.** The perforated suction anchor

perforation height is 0.5m, and this is located at the lower part of the suction anchor (0.9 < *z/h* <1).

To investigate the effectiveness of the perforated suction anchor on reducing the development

The numerical analysis shows that the excess pore water pressure appears outside of the anchor, while negative pore water pressure appears inside. According to the principle of effective stress, the soft clay structure on the external anchor wall is degraded followed by the degradation in strength. The uplift capacity of suction anchor gradually decreases with the development of excess pore water pressure. According to the distribution characteristics of the residual pore pressure, a perforated anchor is proposed based on the traditional suction anchor, as shown schematically in Figure 15. Perforation at the lower part of the anchor wall is helpful to reduce the accumulation of excess pore water pressure. The installation process of the suction anchor is divided into two stages. First, the suction anchor is installed by self-weight to around half the design depth, and then negative pressure is applied until the anchor reaches the final depth [37,38]. Perforation is located at the lower part of the suction anchor, and therefore, the new structure style

**Figure 16.** Comparison of residual pore pressure distribution between the traditional anchor and the perforated anchor. **Figure 16.** Comparison of residual pore pressure distribution between the traditional anchor and the perforated anchor.

#### Figure 16 shows a comparison of the residual pore pressure distributions between the **6. Concluding Remarks**

traditional anchor and the perforated anchor. As shown in Figure 16, the accumulation of excess pore pressure outside of the perforated anchor is reduced remarkably, compared with the In this study, numerical simulations were conducted to investigate the buildup of pore water pressures in a soft clay seabed around a suction anchor under cyclic loading conditions. Based on the existing two-dimensional bounding surface model, a three-dimensional bounding surface model was proposed to describe the cyclic behaviors of soft clay. Based on the analysis results obtained, the most significant conclusions can be summarized as follows:


**Author Contributions:** Data curation, C.H.; Methodology, H.L.; Software, J.L.; Writing—review and editing, X.C. and S.W.

**Funding:** The authors are grateful for the financial support from the Distinguished Young Scholars (Grant no. 51625902), the National Natural Science Foundation of China (Grant no. 51379196), the Young Elite Scientist Sponsorship Program by Cast (Grant no. 2016QNRC001) and the Taishan Scholars Program of Shandong Province (Grant no. TS201511016).

**Conflicts of Interest:** The authors declare no conflict of interest.
