# Assessment of Pohang Earthquake-Induced Liquefaction at Youngil-Man Port Using the UBCSAND2 Model
## 4 Conclusions  
Since the widespread damages on geotechnical structures caused by liquefaction during the Pohang earthquake, the understanding of the mechanism and more accurate predictions of liquefaction-induced displacements using state-of-the-art numerical tools have played crucial roles in the design stages for practical engineering applications. In this study, a robustly practical model called UBCSAND2, in which two-mobilized planes (i.e., the maximum shear plane and horizontal plane) simultaneously participate in plastic strain generation, addresses the conventional effects in the element CDSS test: rotation of principal stress and plastic unloading.  
The UBCSAND2 model was calibrated by a series of CDSS tests. There is a good agreement between the experimental and estimated results either in variations of \(CSR\)-\(N_{\text{liq}}\) curves or in terms of stress path, shear stress-shear strain, and pore pressure generation under different density states (\(D_{\text{r}}\)), confining stress (\(\sigma^{\prime}\)v), and initial static shear stress (\(\alpha\)) conditions. The generic parameters of the model were chosen to assess the liquefaction that occurred at Youngil-man port, Pohang, Korea.  
The quay wall in the region of Pohang in South Korea was numerically simulated to demonstrate capabilities of the UBCSAND2 model in predicting the mechanical behavior of liquefied soils. According to the numerical results, liquefaction mostly occurred in silty sand layers when the excess pore water pressure generated almost 85-95% of initial vertical effective stress. The displacements at the top of the quay wall from liquefaction phenomenon were approximately 20 and 3 cm, respectively, when the settlements of reclaimed area behind the quay wall varied nearly from 4 to 8 cm. These numerical results obtained from the analysis are extremely similar to that observed by solely visiting the sites after the Pohang earthquake. The mechanism of excess pore water pressure generation, shear band expansion, shear stress-strain response, and transmission waves obtained from the numerical analysis have provided a full understanding of the liquefaction phenomenon that occurred in Youngil-man port.  
Conceptualization, N.-P.D. and S.-S.P.; methodology, N.-P.D. and S.-S.P.; software, N.-P.D. and S.-S.P.; validation, N.-P.D., S.-S.P. and D.-E.L.; formal analysis, N.-P.D. and S.-S.P.; investigation, N.-P.D. and S.-S.P.; resources, S.-S.P. and N.-P.D.; data curation, S.-S.P. and N.-P.D.; writing--original draft preparation, N.-P.D.  
Figure 24: Acceleration responses of the observed nodes in the analysis: (**a**) input motion, (**b**) node N2, (**c**) node N3, and (**d**) node N4.  
and S.-S.P.; writing--review and editing, N.-P.D., S.-S.P. and D.-E.L.; visualization, N.-P.D. and S.-S.P.; supervision, S.-S.P.; project administration, S.-S.P. and D.-E.L.; funding acquisition, S.-S.P. and D.-E.L. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. NRF-2018R1A5A1025137).  
The authors declare no conflict of interest.