CO Editor

Suggestions for revision or reasons for rejection

November 15, 2017

Dear Editor, dear Authors:

General comment: The manuscript has improved from the first version, but still has lingering issues that need to be addressed and does not contains enough details to make the analysis fully understandable.

Specific comments:
1)Several issues with sentence structure and grammar still persist. I would recommend a further English edit to improve sentence structure and terminology.

2)The authors use (in the title and at some points in the text, e.g. page 3, line 9) the term hazard assessment to describe their analyses. Since the rock fall hazard assessment requires specific data (e.g. frequency and magnitude) and further analyses (e.g. trajectory modeling) that are not presented in the text, I would suggest remove it from the title and the text. Please be specific and use the appropriate terms in the description of the analysis.

3)It is not clear from the text how the model obtained with RPAS based photogrammetry was validated using TLS data and which is its accuracy. Please explain the method adding specific details.

4)The authors state that “the rock mass failure was analyzed with the RocFall FEM software of the Rocscience (RS2)”. For what I know the RocFall software is a trajectory simulation software and does not allow to analyze the stability of a slope. Please verify and in case modify the text.

5)It is not clear from the text how discontinuity measurements were extracted from the RPAS based photogrammetric model. This is a key aspect to underline the potential of using the RPAS based photogrammetry in rock slope stability analysis and kinematic analysis of discontinuity sets. Please clarify.

6)At line 7 of page 8 (and in the flow chart of figure 4) the authors state that “Risk assessment was based on slope stability calculation” but no risk analysis is presented. Please modify the text considering the real contribution of the analysis.

7)The authors state that “six main joint sets (…) were identified with prevailing NE-SW direction” and refer the text to figure 7. From the text, it is not clear what criterion is used to show joint measurements (e.g. dip/strike or dip/dip direction); it seems that measurements in the text are indicated as dip/dip direction and in the rose diagram of figure 7 as dip/strike (it is not obvious for the reader). Moreover, for what I can understand looking at figure 7, it shows only 5 joint sets and two of that have a very similar strike (I suppose strike 312 and 299). Please clarify this aspect adding specific details in the text and in the caption of figure 7.

8)In the cross sections of figure 8, the authors indicate the total displacement (see caption) with color ranging from blue to red and do not show any color scale to relate displacement values to colors. In this way, it is not clear what the reader should conclude looking at the analysis, also considering that despite the safety factor is above 1 the slope is subject to deformation. Please clarify this aspect and show the result of the stability analysis for all of the selected cross sections.

9)In the conclusions the authors state that “According to 2D FEM modeling the intercalating low strength layer is one where potential slip surface can develop causing larger scale mass movements, but at present it has low probability”. Even if this interpretation might be consistent with a modeled spatial distribution of the safety factor (that is not shown in the specific figure), in my opinion the result of the global stability analysis is not suitable to estimate the probability of occurrence of a landslide. Please modify the sentence or remove.

With the above corrections, I feel the manuscript may be reconsidered for publication.

Interactive discussion

Peer-review completion