Assessment of Pohang Earthquake-Induced Liquefaction at Youngil-Man Port Using the UBCSAND2 Model
Round 1
Reviewer 1 Report
Paper review "Assessment of Pohang Earthquake-induced Liquefaction at Youngil-man Port using the UBCSAND2 model" by Nhat-Phi Doan, Sung-Sik Park and Dong-Eun Lee
The paper shows an application of constitutive model UBCSAND2 to incorporate shear-induced effects in both loading and unloading as well as principal stress rotation effects. The authors discusses the calibration of UBCSAND2 via cyclic direct simple shear (CDSS) test results of Pohang sand, which was collected from liquefied paddy fields due to the 2017 Pohang earthquake (Mw = 5.4) in South Korea. Although arguable, the authors restrained to simple shear conditions claiming they best reproduce realistic earthquake loading. In a second phase, UBCSAND2 model is employed to assess the liquefaction-induced damages occurred at the
quay wall and backfill layer near the epicenter of the Pohang earthquake.
Main issues:
(1) In the Introduction, the authors claim that several constitutive models for soil behaviour have been developed with the advancement of computer technology. This reviewer disagrees since very complex soil non-linear models have been analytically developed since the 50s. A little bit more of literature review would help (e.g. Aubry, D. & Modaressi, H. Seismic wave propagation in soils including non-linear and pore pressure effects. Recent Advances in Earthquake Engineering and Structural Dynamics, V. Davidovici (ed.), Ouest Editions, 1992, 209-224)
(2) In the Introduction, the motivation the authors brought to support their choice of UBCSAND2 as a promising tool seem quite weak. The paragraphs showing pros and cons of this model must be improved to strengthen the choice made.
(3) References to constitutive models are loose and not well referenced. For instance, citing the Mohr-Coulomb criterion, by referring to it as "Mohr-Coulomb model incorporated in the FLAC program" is quite an aberration. constitutive models must be referenced precisely, independently from the softwares employed to implement them, which must be briefly referenced only in the numerical test sections (they are commercial codes).
(4) There are no equations! The paper is quite impossible to follow with no equation nor detail explanation of each parameter to be calibrated (section 2).
(5) Besides lack equations, the calibration procedure needs to be demistified. For instance, there's no comment on the lack of hysteresis loops in Figure 2b, compared to experimental results. The numerical model does not fit the pore-pressure small oscillations, following the main trend. How does this affect the transient soil dynamics? For anisotropic stress states, in Figure 2a, 3a, 4a and 5a, the rapid stress drop is quite slower compared to experimental results (or at least, more cycles are needed before reaching the slow drop to initiate). This can be crucial to assess the failure initiation and the pre-failure settlements. How do the authors comment on this?
(6) Ground motion selection is quite arguable. The impinging wave motion is extracted from recording stations quite far away from the site. No considerations on the eventual ground motion correction to adapt to site conditions were made. This is quite delicate aspect and it can largely affect final predictions.
(7) Finally, the authors claim to have reached more accurate predictions, although they do not mention any comparative study.
Minor issues: see attached pdf.
Final judgement: I do believe that this work is too preliminary to be published. I suggest that the authors should reconsider their next resubmission carefully, since too many flaws and obscure points are present at ths stage.
Comments for author File: 
Comments.pdf
Author Response
See the attached file.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The article "Assessment of Pohang Earthquake-induced Liquefaction at Youngil-man Port using the UBCSAND2 Model" is of practical importance for assessing the negative consequences of changes in geotechnical conditions. The results of laboratory experiments performed by the authors were used to calibrate the UBCSAND2 model. Based on the obtained model, a numerical analysis of soil liquefaction recorded during the passage of seismic waves from Pohang earthquake was carried out. The proposed scientific and methodological approach to the analysis of excess pore pressure is recommended to be tested for the predictive assessment of the mechanical behavior of soil liquefaction at other objects.
Author Response
See the attached file.
Author Response File: Author Response.docx
Reviewer 3 Report
The draft discussed the soil liquefaction simulation using UBCSAND2 model. The following unclear parts must be carefully checked:
- Line 31, “However, to date a reliable prediction…has still been challenging”, what kinds of challenges?
- Line 84, “characteristics and resulting displacements due to dynamic loading”, the English of “resulting displacements” is strange.
- P. 3, Line 103, “Upon providing input parameters of the soil skeleton….the seismic behavior of sand can be predicted”, add the references to support the sentences.
- P. 5, Line 158, “…the initial static shear stress bias (i.e., alpha>0)”, the alpha must be defined when it comes out for the first time.
- P. 9, Line 219, “Fig. 9 presents the representative cross section of …”, is the cross section the north-south or the east-west direction?
- In Fig. 9, draw the boundary condition in the figure. In addition, how to set the water table in the study?
- References for Eq. 2 must be added.
- It is not clear that how the authors set the quiet boundaries. Is the quiet boundaries at the bottom of the model in X and Y directions? And, what are the setting in the lateral boundaries?
- P. 11, Line 281, “considering material types as 0.5% for weathered rock, 3%...0.5% for liquefiable soil layers…”, how to get the values for the study? Detail explains are required.
- P. 2, Line 60, “using standard penetration test or cone penetration test (CPT) data”, in Fig. 9, the cross section of the port is shown. The reviewer suggested the authors add the SPT data, borehole drilling profile, fine content and water content of the silty sands, LL and PL of the fine content, and the CPT profiles (qc, sleeve friction, pore pressure) (the SPT borehole should be close to the CPT) to help the reader better judgement of the correctness of Fig. 9, realize the physical characteristic of local soil, and verify the correctness of soil liquefaction in Fig. 11. Without verification of the simulation results to the real situation, it is hard to judge the contribution of this study. In addition, the ground displacement data should also added if the data exist.
- Find a native speaker to sharp the English of the draft.
Author Response
See the attached file.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
I have the feeling that some of the key questions of the first review have been left unanswered :
(1) Ground motion selection is quite arguable. The impinging wave motion is extracted from recording stations quite far away from the site. No considerations on the eventual ground motion correction to adapt to site conditions were made. This is quite delicate aspect and it can largely affect final predictions. Have you considered deconvolution if the input motion was recorded at free-surface?
(2) Despite being added into the Appendices, some of the model equations must be introduced in the main text to let the reader follow the different calibration steps
(3) I disagree with the authors concerning the initial spurious (2) waves simulated at t=0. Those spurious waves must disappear by either considering filtering, either preprocessing the initial input motion (filtering, base line correction, padding). Figure 8: the Fourier's spectrum must be in loglog scale.
(4) You introduce critical damping without mentioning any calibration on G-gamma-D degradation curves. Those curves are necessary for any basic soil dynamics analysis and must be added to strengthen the paper quality
Author Response
See the attached file.
Author Response File: Author Response.docx
Round 3
Reviewer 1 Report
To this reviewer, the paper at this stage can be published. The authors have improved it considerably.
