Experimental Study on the Shear-Flow Coupled Behavior of Tension Fractures Under Constant Normal Stiffness Boundary Conditions
Round 1
Reviewer 1 Report
The reviewer suggests the manuscript be accepted as it is.
Author Response
Thanks for your reviews.
Reviewer 2 Report
The paper presents tests for rough joints to investigate the effects of surface roughness, normal stiffness and initial normal stress on shear "displacement" behavior and hydraulic behavior of joint. The experimental results are interesting, however the paper lacks comparison with theoretical models.
My recommendation is to accept in present form, taking into account the significance of experimental work.
Author Response
Attached file is the response for reviewer 2 comments.
Author Response File: 
Author Response.pdf
Reviewer 3 Report
Reviewer comments:
Technical Note 1
Experimental study on shear-flow coupled behavior of joints under constant normal stiffness boundary conditions
Changsheng Wang, Yujing Jiang, Hengjie Luan,Jiankang Liu, Satoshi Sugimoto
Line 18 ‘and HIGH ? initial normal stress condition…
Line 21…slow growth stage…
Line 30….based on the title, and the very recent date (2018) of Ref.2 it does not seem to be a good introductory reference for this decades old subject – but undoubtedly important for the later CNS argument caused presumably by rock bolting/anchoring. A more general paper on shear, dilation, permeability, mechanical and hydraulic apertures of rock joints (as opposed to tension fractures) could be Barton, Bandis, Bakhtar, 1985. A. Makurat was shearing and flow-testing (actual rock) joints since 1985, and some papers of his from 1990 (Loen conference) pre-date those given by the authors, which of course are later key references.
Line 50, 57. In view of statement in Line 50, suggest Line 57 could read: Some…..CNS
Line 63….doubt that shear strength decreases…dilation of course
Line 73….need to be further investigated…
Line 77 ….MPa/mm is more understandable than GPa/m
Line 82…..actually authors have used artificial tension fractures, rather than joints…..so maybe title of Technical note should be ….behaviour of tension fractures under….(but now see: should be replicas of tension fractures…?) – you see how the reviewer/reader is confused by the present title.
Line 84, 85 Sentence needs to continue….geometry, (. The ) artificial replicas
Re plaster-water replicas for ‘rock’. This composition is very ‘simple’ and ignores many studies in the past in which more sophisticated model materials were used, including e.g. fine sands, ballotini, high-density powders etc. There were no ‘dimensional analysis’ attempts? E/UCS = 1000……quite high.
Line 91. Replica surface geometries…..Line 93….strictly speaking: replicas of tension fractures…..not joints, since artificial on two counts
Line 94…replicas…..replicas
Line 99 ….the calculated/estimated JRC for the replicas is very low compared to conventional tension fractures – maybe the authors should have commented upon this positive aspect – i.e. the replicas are more realistic than the reviewer has feared up to now. However, the mild critique of the use of just gypsum/plaster remains.
Lines 11, 12, 13, 15, 16, 17 of the Abstract are now understood to be quite misleading in view of: moderate roughness, not rock joints, actually gypsum replicas
Figure 1. As drawn (conceptually of course) the applied shear stress will tend to cause a moment, thereby making the normal stress application non-uniform. Is this – in practice – avoided, by shear-force application in the plane of the joint? Could comment?
Line 120….on the two sets of replicas with their different roughness….
Figure 2. All the diagrams give normal stiffnesses as GPa/m, which is more easily interpreted as MPa/mm – then one can understand that the constant (?) normal stiffnesses applied are actually quite limited.
Note – figure caption of Figure 2. The authors should not write ‘rock joints’ – needs correction throughout Technical Note.
Line 156, 163 etc …replica surface…
Line 175, 183, 190, 191....replicas G1 and G3…
Figure 3. The behaviour of the rougher replica with ‘increasing’ shear strength after the drop from peak suggests an incorrect normal stress application (or incorrect correction?) as shearing continues. There is no logical reason for strength not to be gradually dropping post-peak, as in DST in general.
Line 193…creates…
Figure 4. Stiffnesses of MPa/mm are suggested, but of course GPa/m is less easily understood as actually quite ‘soft’.
Line 208/209 …this assumption of equality is unlikely to be correct. See e.g. Barton et al. 1985 conversion between the two apertures. The biggest differences are when the apertures are << 1mm i.e. when very small.
Lines 221-223…..good that this is consistent, and logical, despite question re lines 208/209
Lines 227, 228….replicas G1…replicas G3
Author Response
Attached file is the response for reviewer 3 comments.
Author Response File: Author Response.pdf
Reviewer 4 Report
The manuscript “Experimental study on shear-flow coupled behavior of joints under constant normal stiffness boundary conditions” describes a series of shear experiments performed on replicated rocks fractures to understand the relationships between fracture behavior and stressing conditions during shear.
The introduction does not include some recent work looking at actual rock fracturing event during shear which I think are worth including. For example, both, Frash, L. P., Carey, J. W., Ickes, T., and Viswanathan, H. S. (2016). High-stress triaxial direct-shear fracturing of Utica shale and in situ X-ray microtomography with permeability measurement. Journal of Geophysical Research. And Frash, L. P., Carey, J. W., Ickes, T., Porter, M.L., and Viswanathan, H. S. (2017) Permeability of fractures created by triaxial direct shear and simultaneous X-ray imaging, ARMA 2017 would be good to reference. There are several other publications by other groups covering this topic that may be worth referencing as well.
CNS, peak shear and residual shear are introduced in the introduction with no good explanation as to what these values refer to. CNS is not well described in the entire document.
Line 21: “slowly” should be “slow”
Line 28: Should read “Underground fracture rock masses consist of intact rock …”
Lines 52 and 97: “slop” should be “slope”
Line 152: “duo” should be “due”
Line 122: Table 2 is referenced but was not included in the manuscript I was given to review. This is a big omission.
Lines 143-144 and 155-156 both talk about relationships between joint roughness and normal stresses in a way that is unclear and is vague to the reader
Equation (6) does not appear correct. The w in the denominator of the middle equation is perhaps misplaced? The value e_h is not defined and likely should be b_h as defined above.
Line 181 refers to Equation 3, but I think Equation 5 is the proper equation
The authors never state is the length value used for T and b_h calculations are changed during the shearing process. I assume this to be the case, but it should be explicitly stated.
In addition, I'm not convinced Processes is the right journal for this manuscript. Note that none of the referenced material is from Processes and that there is a rich amount of literature in other journals that covers this topic.
Overall, it’s an interesting bit of work, but the presentation needs work and I recommend revisions prior to publication. I think the authors would be best suited to attempt to publish in a journal that is more widely accepted by the scientific community as routinely dealing with this subject matter as well; again, looking at the referenced journal articles as a guideline.
Author Response
Attached file is the response for reviewer 4 comments.
Author Response File: Author Response.pdf
