Geotechnical and Geophysical Assessment of the 2021 Tamban Chimbo Landslide, Northern Andes of Ecuador

Round 1

Reviewer 1 Report

The paper concerns the characterisation of a landslide in Ecuador via geophysical and geotechnical surveys. The paper is well written and in the scope of the journal. However some revisions are needed about the geophysics chapter and some graphics.

-Fig.3 not clear the ert survey lines in the map

-chap.4 Authors refer to gradient method without explaining the skip used. No information are given about the error estimation of the several dataset, nor the inversion error considered for the final plot sections. Authors used horizontal geophones, but did not explain which horizontal source they adopted. Moreover they used MASW method, but without explaining in which configuration. Rayleigh waves cannot be detected with transversal sensors. Not clear what they intend for 'artificially generated microtremors'. No information about (tomograhic?) seismic inversion was provided, and no seismic section are shown. 

-fig.7 is not clear and caption not sufficient, there are numbers, formula and text. Change color for different unit

Ln395-400 are in spanish!  It makes the chapter not understandable

-fig8 and 9 and 10 use similar colour for u2-u3, seem just snapshot of software output. This figure should be improved.   

I think overall moderate revisions are needed

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

This article presents a geotechnical and geophysical study of the 2021 Tamban Chimbo landslide. In this paper, the cause of the event was analysed in detail with a reconstruction of the lithological units through post-event geotechnical tests, geophysical analysis and the site-specific anthropogenic effects. A numerical model has been exploited for slope stability analysis considering technical specifications.

General comments:

Although the goal of the article is clear, the organization of the work can be improved with some revision. The order of the chapters does not follow a very clear logic. We talk about the specific area and the specific event, and then in chapter 3.2 go on to talk about the generic causes of landslides in the area (also mentioning earthquakes in the first part). The second part of Chapter 3.2, on the other hand, returns to the specifics of the event by mentioning the moderate rainfall that occurred for 11 days and the culvert rupture that occurred in the preceding months. In this case, there is no mention of a clear date or at least a month regarding the pipeline rupture, although this is very relevant information.

For what concerns the rainfall event, it would be interesting to get an idea of rain intensities from other stations in areas as close as possible to understand how much of the collapse is affected by this event and to compare it to others.

In line 88 together with the papers already cited, it can be interesting to cite works that are an example of integrations between different approaches, methods and techniques, in obtaining data. This aspect may be of relevant importance if you want to go to the methodology for further landslide scenarios.

Panzeri, L., Mondani, M., Taddia, G., Papini, M., & Longoni, L. (2022). ANALYSIS OF SNOWMELT AS A TRIGGERING FACTOR FOR SHALLOW LANDSLIDE. International Multidisciplinary Scientific GeoConference: SGEM, 22(1.1), 77-83. DOI: 10.5593/sgem2022/1.1/s02.009.

This paper aims to study the evolution of shallow landslides affected by snowmelt
and rainfall and to compare the observations done in situ by means of a statistical analysis
of meteorological variables with those made in the laboratory.

Godio, A., Strobbia, C., & De Bacco, G. (2006). Geophysical characterisation of a rockslide in an alpine region. Engineering geology, 83(1-3), 273-286.

In this article, for example, a combination of geophysical methods has been used for the characterisation of a rockslide area. The results have been calibrated by comparing the geophysical responses with the geological evidence derived from boreholes and with the movements recorded using an inclinometric probe.

Chambers, J. E., Gunn, D. A., Wilkinson, P. B., Meldrum, P. I., Haslam, E., Holyoake, S., ... & Wragg, J. (2014). 4D electrical resistivity tomography monitoring of soil moisture dynamics in an operational railway embankment. Near Surface Geophysics, 12(1), 61-72.

In this article, the internal moisture dynamics  of  a railway  earthwork  embankment are investigated using 2D and 3D resistivity monitoring. Visualization of the data as 2D sections, 3D tomograms and time  series plots  for  different zones  of  the  embankment  enabled  the  development  of  seasonal wetting fronts within the embankment to be monitored at a high-spatial resolution and the respective distributions of moisture in the embankment to be assessed. Although the dike considered here is at no immediate risk of failure, the approach developed for this study is equally applicable to other more high-risk earthworks and natural slopes. Could be an interesting point of discussion!

Could be an interesting point of discussion!

Minor comments:

Line 20: aims – have

Line 78: followed by

Line 139: resulted in

Table 1: highlight the “Sum”

Line 167-168: the case study is neither in a densely populated urban area nor in industrial sectors in development.

Line 213-214: “Later a fill material without technical specifications has allowed partial circulation, however, this work would be most likely affected by the next winter months that begin in December.” The sentence is not clear.   Please rephrase.

Line 222: I would say “predisposing factor” instead of geological factors.

Line 271: Describe the choice of the different types of arrays (why Wenner or Wenner-Schlumberger?) in the different parts of the landslides. Depth of investigation? Signal-to-noise ratio?

Line 327-331: the sentence is too long. Please rephrase.

Figure 7: “rupture zone” instead of “zona”

Line 374: it is meaningless to put 1.46 Ωm as a reference value for the resistivity. This is just the lower value in the legend of the P1 (figure 6). The blue colour refers to values below 18 Ωm and it is not clear which is the exact one. Therefore, a value of 1.46 seems to be very low considering water coming from the sewage system. In addition to that, I will change the colour scale, because the lower and the maximum values seem to be similar (blue and violet).

Line 394 -407: test written in Spanish! Remove it and maintain the one written in English below.

Moderate editing of English language required

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The topic and the study area of this work are very interesting. The integration of geotechnical and geophysical measurememts  is a key action to characterize the landslide geometry and to investigate the dynamics of the slope failures. 

Then, papers about this topic are welcomed and must be encouraged.

However, I have to point out many critical aspects.

1) The main objective of the paper is the study of the Tamban landslide, but the authors introduced a lot of generic information about the regional context and the triggering factors of landslides. A short introduction could be sufficient.

2) The description of the ERT tomographies and the sesismic measurents  are too generic, it is mandatory to introduce more details and to  better describe  the results. The novelty of the results is not emphasized.

3) The numeric modeling is obscure, it is very hard to follow a logical scheme. 

4) What is the real contribute of the geopphysical mearurements to the slope stability analysis?

The overall organization of the paper is quite poor and English form strongly requires a deep and accurate revision.

Starting from line 56 the use of the numeric labels is not appropriate.

The sub-paragraph 2.3 is missing or the numbering of the sub-paragraph is wrong.

Line 387 The term "three" is not appropriate in a scientific context. 

Line 395-407 The language is not English!

I strongly encourage the authors to perform a deep and accurate revision of the paper.

The English form is quite poor, a complete revision is mandatory

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Dear authors,

I greatly appreciated your work for improving the overall organization of the manuscript. However, some critical problems still remain.

I kindly requent you a point-to-point reply, your response is quite vague and the comments are partially considered.

Furthermore, the new phrase "The testing techniques...." about the geoelectrical array is not appropriate (see line 385). I suggest "The array configurations adopted for the field measurements are....."

There is again an excessive use of number-indexed sentences and literal numerical values in scientific articles are not appropriate.

The English form strongly requires another review. 

Author Response

Dear expert reviewer,

we have taken very seriously your second review report, and therefore, we are responding all your comments individually as you will see in our response-letter. All our comments are in cursive, following one by one, all your requests or questions of both .

The topic and the study area of this work are very interesting. The integration of geotechnical and geophysical measurememts  is a key action to characterize the landslide geometry and to investigate the dynamics of the slope failures. 

Then, papers about this topic are welcomed and must be encouraged.

Response: We could not agree more, thanks a lot.

However, I have to point out many critical aspects.

1) The main objective of the paper is the study of the Tamban landslide, but the authors introduced a lot of generic information about the regional context and the triggering factors of landslides. A short introduction could be sufficient.

Response: Dear expert reviewer, as you could certainly appreciate, we extended the introduction, as one of the colleague reviewers not only asked us to extend, he or she pre-edited what should we and how extend, including some new mentioned references. Therefore, we opted rather to extend than to shorten, as requested.

2) The description of the ERT tomographies and the sesismic measurents  are too generic, it is mandatory to introduce more details and to  better describe  the results. The novelty of the results is not emphasized.

Response: For the electrical tomography test, three geoelectric profiles were conducted, being of 200, 205 and 315 m in length, respectively, applying Dipole, Schlumberger, Gradient and Wenner measurement techniques. The electrical method (electrical resistivity tomographies) consists of establishing the curves of resistivity variations with the depth of the ground, through measurements on the surface, as these measurements were realized with an ABEM Terrameter LS 3000 subsoil resistivity meter owned by the state entity Secretariat of Risk Management of Ecuador. There up to 63 electrodes were used with spacing between 4 to 5 m, then injecting a maximum current intensity of ± 600 V and 2500 mA, which allows identifying electrical resistivity anomalies in the different subsoil materials. Data processing and inversion of electrical tomography models are developed from the RES2DINV software. Additionally, these methods allow delineating geological structures of discontinuities such as geological faults, joints and lithological contacts (both at depth and near the surface).

3) The numeric modeling is obscure, it is very hard to follow a logical scheme. 

Response: The numerical model to obtain the stability analysis and design of remediation measures follows the established methodology that details the integration of the data collected in the field and laboratory through the surveys described together with details of local regulatory parameters in the respective software. processing and modeling indicated in lines 81 to 87 and 367 to 390.

4) What is the real contribute of the geopphysical mearurements to the slope stability analysis?

Response: Dear expert reviewer, the geophysical prospecting as mentioned in our manuscript, allows building a geological model, outlining lithological contacts and discontinuities such as geological faults. This (our) model allows differentiating lithological units that are associated with laboratory tests from triaxial analyses, as you may appreciate in the text and corresponding figures.

The overall organization of the paper is quite poor and English form strongly requires a deep and accurate revision.

Response: As you could read, we have had a native speaker who went once again through the text and corrected or re-edited the entire text on many, many spots. I hope, you liked this new version more than the very first one.

Starting from line 56 the use of the numeric labels is not appropriate.

Response: Changed, eliminated as asked

The sub-paragraph 2.3 is missing or the numbering of the sub-paragraph is wrong.

Response: This has been corrected, thanks for advising

Line 387 The term "three" is not appropriate in a scientific context. 

Response: It is, as all numbers until twenty need to be expressed a words. Also for expressions as thirty, forty…hundred etc. This is not only a rule of the English language, its also part of the conditions of the journal. Sorry, it needs to remain as it is

Line 395-407 The language is not English!

Response: Corrected, our mistake in the submission.

I strongly encourage the authors to perform a deep and accurate revision of the paper.

Response: Done as requiered

Dear authors,

I greatly appreciated your work for improving the overall organization of the manuscript. However, some critical problems still remain.

I kindly requent you a point-to-point reply, your response is quite vague and the comments are partially considered.

Response: As you certainly have seen, we were much more punctual to your request on point to point responses.

Furthermore, the new phrase "The testing techniques...." about the geoelectrical array is not appropriate (see line 385). I suggest "The array configurations adopted for the field measurements are....."

Response: Changed as requested

There is again an excessive use of number-indexed sentences and literal numerical values in scientific articles are not appropriate.

Response: Corrected as asked