Roof Subsidence and Movement Law of Composite Strata Mining: Insights from Physical and Numerical Modeling
Round 1
Reviewer 1 Report
The topic of the paper is not new, and many publications exist dealing with the prediction of the subsidence over longwall coal mine over the word, including China.
The paper should be deeply improved, different critical aspects should be Added:
1- additional details concerning the geology of the studied area, and information of the boreholes used for constructing the physical model.
2- additional information about the laboratory tests to characterise the rock and the equivalent materials used in the physical model
3- additional information about the monitoring system, mainly the optic fibre, what is the utility and what is the difference of the different Survey points used to follow the subsidence through different depth
4- what is the method used to excavate the mine? add images to observe the development of goaf, cracks, etc. It is absolutely necessary to compare the physical and the numerical results with existing conceptual models (see NCB, 1975, Reddish and al.)
5- few information was given concerning the field test, what are the origin of the data, it is absolutely unclear, and we can't use them without additional dat.
7- what are the role of the loading system?
8- the numerical model is elastic model, without presenting the goaf zones, what are the main assumptions.
9- the results in the current situation are not useable for predicting the subsidence over the mine.
10- update the state of the art using international publications concerning the numerical and physical modelling over underground coal mines.
In conclusion, the paper should be improved completely before to take into account the details regarding the vocabulary used by the authors such as settlement instead of subsidence, etc.
Author Response
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Reviewer 2 Report
- Please, delete a first part of title of the figure 1: "Figure 1. This is a figure. The coalfield structure map of Zhangji mine."
- Description of a physical model and the measuring devices made in the 2.3.1. point is too general - e.g. provide details about camera parameters
- Boreholes in situ should be done above the 11418 longwall - how can be done comparison of the layers profiles coming from boreholes located around a mining excavation with the layers in a physical model in laboratory which are directly located above emptiness? (just for thinking)
- Inclination in situ is 4 degrees and in a numerical analysis 10 degrees (why?). Can we compare these results? What for simulations with 20 and 30 degrees? Exploitation rather isn't carried out in so great inclinations.
- Lack of the third part in the article, namely real results of vertical and horizontal displacements of points which can be done by the use of classical geodesic measurements or aerial methods (UAV, InSAR -> photogrammetry methods).
- Literature - please, cite works of Bernard Drzezla or Litwiniszyn about experimental models (physical models) from laboratory, works of Stanislaw Knothe, Jan Bialek or Marek Wesolowski about numerical models and their accuracy (Justyna Orwat or Andrzej Kowalski).
- Figure 24. The horizontal movement curve of the rock formation at four angles: (a) Dip agle 0°; (b) Dip agle 10°; (c) Dip agle 20°; 426
(b) Dip agle 30°. <- here should be "d"
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The authors state that the average uniaxial compressive strength of natural rock mass is 28% of the indoor intact rock, thus, the natural rock mass strength has been obtained (lines 144-146). However, there is no basis for such a statement since the strength of natural rock mass is dependent primarily on the rock jointing which may be very changeable. For example, according to other researchers, this strength is typically only 10–20 %. This parameter usually varies from 10 to 80%. But this parameter is not a constant for the rock and has differences for different rock types. Usually, a rock mass strength is a function of relative scale and a degree of fractured disturbance. You should explain why in your case it is 28%.
In addition, it should be explained how this parameter is taken into account in your models, as table 1 shows only the strength of the rock samples. For example, Coal Rc=15 MPa - it is a strength of coal sample but not coal mass strength (15 MPa can’t be 28%).
Only the laboratory uniaxial compressive test results are not sufficient to create a similar physical model, especially in the modelling of stratification and collapse of composite rock formations. The tensile and shear strength should be taken into account. In accordance with similarity theory, the tensile and shear relation of the model and the prototype must also be fulfilled. In fact, it is almost impossible to meet all these requirements. Thus, the physical equivalent material model does not produce accurate results and it is generally used only for the principle assessment of cracking and collapse.
In the analysis of processes in composite rock formations, using both numerical research and physical modelling, special attention should be paid to the modelling of contacts between rock layers. You should explain how it was taken into account in the numerical and the physical modelling.
In the conclusion of the manuscript, the authors state:
1) an in-depth understanding of the typical mechanism of composite rock settlement and horizontal movement was obtained;
2) the combination of a similar material physical model and finite element numerical modelling is an effective method to study the settlement and movement behaviour of composite rock formations.
Actually, the combination of several modelling techniques gives a more accurate result. However, this is true only if all the shortcomings of each of the research methods are taken into account and the results of the research are compared with the result of a field monitoring. The strengths and weaknesses of the numerical modelling and the physical (similarly) modelling should be noted and the impact of disadvantages of these modelling techniques on the results explained.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Thank you for improving the paper.
