Use of a remotely piloted aircraft system for hazard assessment in a rocky mining area (Lucca, Italy)

Salvini, Riccardo; Mastrorocco, Giovanni; Esposito, Giuseppe; Di Bartolo, Silvia; Coggan, John; Vanneschi, Claudio

doi:https://doi.org/10.5194/nhess-18-287-2018

Articles | Volume 18, issue 1

https://doi.org/10.5194/nhess-18-287-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue:

The use of remotely piloted aircraft systems (RPAS) in monitoring...

https://doi.org/10.5194/nhess-18-287-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 18, issue 1

Research article

|

19 Jan 2018

Research article |

| 19 Jan 2018

Use of a remotely piloted aircraft system for hazard assessment in a rocky mining area (Lucca, Italy)

Riccardo Salvini, Giovanni Mastrorocco, Giuseppe Esposito, Silvia Di Bartolo, John Coggan, and Claudio Vanneschi

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Final revised paper (published on 19 Jan 2018)
Preprint (discussion started on 14 Jun 2017)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Review of nhess-2017-194', Anonymous Referee #1, 05 Jul 2017
- AC1: 'Point-by-point response to Reviewer #1', Riccardo Salvini, 21 Aug 2017
RC2: 'Comment on NHESS-2017-194', Anonymous Referee #2, 13 Jul 2017
- AC2: 'Point-by-point response to Reviewer #2', Riccardo Salvini, 21 Aug 2017

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (further review by Editor and Referees) (30 Aug 2017) by Yuichi S. Hayakawa

AR by Riccardo Salvini on behalf of the Authors (19 Sep 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (22 Sep 2017) by Yuichi S. Hayakawa

RR by Anonymous Referee #2 (08 Oct 2017)

RR by Anonymous Referee #1 (16 Oct 2017)

Suggestions for revision or reasons for rejection

General Comments:
Many of the reviewers’ comments on the first submission have been addressed. When they preferred not to apply the reviewers’ comments, the authors generally provided adequate justifications. In my review, I included a few extra minor comments, which the authors should consider mostly to improve clarity of the submission.
At this stage, I recommend minor corrections before publication of the paper. I strongly encourage the authors to proof read the manuscript, in particular Sections 4.2, 4.3, 5 and 6: I made a number of suggestions in the Technical Corrections section below, which could help improve clarity.

Specific Comments:
• Section 3.1, first paragraph: is measurement of the exterior orientation of the camera actually used/necessary in the SfM workflow, or was it used as a check or as calibration? I suggest adding a sentence to clarify.
• Page 11, Line 5: could the authors clarify what they mean by “elaboration speed”. Is it the time to generate 3D models, or the time to characterize discontinuities?
• Page 11, Line 19: “exact geometrical reconstruction” seems a little bit exaggerated, as I do not think that Swedge allows integration of all the details of block geometry.
• It is not always clear which 3D model the authors are referring to. For example on page 10, Lines 11 to 19 are about both the frontal and the zenithal models. Then, suddenly between Line 10 and 23, the explanation is only about the zenithal model. Between Lines 24 and 26, the sentence is about the frontal model, and then between Lines 26 and 28, the sentence is about both models. I think these paragraphs need to be clarified to make it easier for the reader to follow.
• Similarly, in Section 4.2, which point cloud was used for discontinuity characterization: the frontal model or the zenithal model, or both? Please clarify in the text.
• Figure 8a: why are the authors using the direct toppling method and not the usual planar sliding method? Please modify as appropriate.
• Figure 8b: the analyses are correct. The stereonet show that a number of intersections fall within the failure envelopes, but does not explicitly show which joint set combinations make these intersection. Although the possible intersections are listed in Table 5, it could be useful to plot the great circles of one intersection as an example.
• Section 4.3 and Table 6: I think it is important that the authors provide all the details about the geometry of the block analyzed in Swedge, so that the interested reader can reproduce the results. These parameters could easily be added in Table 6. The following parameters are not provided in the submission: slope dip angle, upper face dip angle and bench width. In addition, it should be made clear which two joints are used for the wedge construction, and if an additional joint is considered as tension crack.
• Table 1: is the pixel size not supposed to be the sensor size divided by the image size? Please modify if appropriate.

Technical Corrections:
• Page 3, Line 22. Please start a new paragraph at “nevertheless”. And, I suggest deleting “nevertheless”.
• Page 3, Lines 11 – 22: this paragraph should be the last paragraph of the introduction, as it presents an outline of the paper content.
• Page 7, Line 28: this sentence has not been corrected as indicated in the authors’ response; please delete “related to manual placement of GCPs”.
• Section 4.2: the 3 first lines are a bit confusing, could the authors please rephrase. I understand that the orientation of 154 discontinuity planes were calculated from the point clouds and plotted on the stereonet, which highlighted four discontinuity sets. And, separately, discontinuity characterization was undertaken in the field based on traditional engineering geological survey.
• Page 8, Line 9: please spell out RMR and GIS as this is the first time they appear in the text. I suggest adding a reference for the RMR.
• Page 8, Line 16: please start a new paragraph at “A discontinuity friction angle”
• Page 8, Line 26: please start a new paragraph at “More than 20”
• Page 10, Line 29: please delete “on the other hand”
• Page 11, Line 21: I suggest starting with a different word, to avoid repetition. For example, the authors could use: “Characterization of the site highlighted a potential significant risk...”
• Page 11, Line 22: please delete “In fact”
• Page 11, Line 24: please delete “Moreover”
• Page 11, Line 26: please replace “motion” with “offset”
• Page 11, Line 29: for clarity I suggest replacing “In this stability analysis” by “In the preliminary limit equilibrium analysis...”.
• Page 11, Line 31: please delete “the” before “removable”
• Page 11, Line 31: please replace “In particular” with “Indeed”
• Page 11, Line 32: I suggest replacing “The rock bridge failure involves the failure or collapse of the intact rock” with “Rock bridge failure involves fracturing of intact rock...”
• Page 12, Line 3-5: please rephrase and clarify this sentence
• Page 12, Line 7: I suggest rephrasing this sentence as follows: “The results of this study are consistent with other studies, where failure back-analyses highlighted low percentage of rock bridges (0 and 5%) at the time of failure (e.g., Frayssines....).
• Page 12, Line 10: this last sentence is repetitive, I suggest deleting it.
• Page 12, Lines 11 to 19: for clarity, I suggest rephrasing this paragraph as follows:” The back calculated rock bridge percentage seems in contradiction with the author’s field observations and their experience in similar contexts, which suggest that a higher percentage of rock bridges may exist. Hudson and Priest (1983) identified two kinds of persistence relative to impersistent or intermittent joints that should be considered. Differently from impersistent joints, intermittent discontinuities consist of joint segments and intact rock bridges on the same plane. Mauldon (1994) claims that the formation of intermittent joints is geologically unlikely, unless a preferential direction of weakness exist within the rock mass. In this case, the cohesion of rock bridges along intermittent joints could be much lower than that of the intact rock, and consequently the percentage of rock bridges could be greater. This could be the case of Block A, and the presence of a series of discontinuities with similar dip and dip direction to the basal plane seems to confirm the hypothesis of a preferential plane of weakness due to the geomechanical characteristics of the marble material in that portion of the mining area (Fig. 13).”
• Page 12, Lines 20 to 29: for clarity, I would suggest rephrasing these two paragraphs as follows:” The progressive degradation with time of rock bridge elements could cause a progressive failure mechanism that has the potential to lead to a final rockfall event. This is particularly important in small engineered slopes such as the present one, where the rock mass may be continuously disturbed by excavation activity driving the slope to instability. Such mechanisms of progressive brittle fracturing of rock bridges are not considered in limit equilibrium approaches, where a small content of rock bridges adds significant apparent cohesion to the failure surface (Elmo et al., 2011; 25 Tuckey and Stead, 2016). Therefore, in case of re-opening of mining activities, an in-depth engineering geological analysis together with the installation of a monitoring system for observing the behavior of the rock mass over time should be considered.
• In the reference list, start a new paragraph before: Priest (1993), and before Sturzenegger and Stead (2009)
• Page 14, Line 30: please delete this keywords, which do not seem to be related to the paper
• Page 17, Line 15: add space between “and” and “modes”.
• Table 3: the caption should read “characteristics of the discontinuity sets measured based on traditional manual engineering geological survey in the study area”. In addition, please spell out JCS and JRC as this is the first time they appear in the text.

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ED: Publish subject to minor revisions (further review by Editor) (17 Oct 2017) by Yuichi S. Hayakawa

AR by Riccardo Salvini on behalf of the Authors (25 Oct 2017) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (09 Nov 2017) by Yuichi S. Hayakawa

AR by Riccardo Salvini on behalf of the Authors (10 Nov 2017) Author's response Manuscript

ED: Publish as is (14 Nov 2017) by Yuichi S. Hayakawa

AR by Riccardo Salvini on behalf of the Authors (22 Nov 2017)

Short summary

Remotely Piloted Aircraft System was used for the engineering geological investigation of a marble mine area in Italy. High resolution images were processed by using SfM techniques for obtaining an accurate and detailed three-dimensional model of the area. Geological and geometrical information was used for a preliminary stability analysis with focus on investigating the contribution of potential rock bridges of two large blocks that pose a potential hazard issue for the workforce.