the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Microstructure-based modelling of snow mechanics: experimental evaluation on the cone penetration test
Clémence Herny
Pascal Hagenmuller
Guillaume Chambon
Isabel Peinke
Jacques Roulle
Abstract. Snow is a complex porous material presenting various microstructural patterns. This microstructure controls the mechanical properties of snow, and this control still needs to be better understood. Recent numerical developments based on three-dimensional tomographic data have provided new insights into snow mechanical behaviour. In particular, the discrete element method combined with the snow microstructure captured by tomography and the mechanical properties of ice has been used to reproduce the brittle properties of snow. However, these developments lack experimental evaluation so far. In this study, we evaluate a numerical model based on the discrete element method with cone penetration tests on centimetric samples. This test is commonly used to characterise the snowpack stratigraphy but also brings into play complex mechanical processes and deformation patterns. We measured the snow microstructure on different samples before and after a cone penetration test with X-ray tomography. The cone test was conducted with the Snow MicroPenetrometer (5 mm cone diameter), which recorded the force profile at high resolution. The initial microstructure and the ice properties fed the model, which can reproduce the exact same test numerically. We evaluated the model on the measured force profile and the displacement field derived from the difference between the initial and final microstructures. The model reasonably reproduced the force profiles in terms of average force, force standard deviation, and the correlation length of the force fluctuations. When the contact law describing ice mechanics is adjusted in the range of reasonable values for ice, the agreement becomes good on all three parameters. The model also well reproduced the measured deformation around the cone tip, which is less sensitive to the contact law parameterization. Overall, the model is capable of distinguishing the different microstructural patterns tested. Therefore this confrontation of numerical results with experimental measurements for this configuration gives confidence in the reliability of the numerical modelling strategy. The model could be further applied with different boundary conditions and used to characterise the mechanical behaviour of the snow better.
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Clémence Herny et al.
Status: final response (author comments only)
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RC1: 'Comment on tc-2023-30', Richard Parsons, 20 Apr 2023
This paper details a methodology to numerically replicate the response of snow particles under cone penetration testing. The authors have shown the validity of this numerical approach which will be beneficial to the community as understanding of processes in the compaction zone is certainly needed to improve interpretation of CPT measurements. I found that in general, the paper read well and was easy to follow, however there are opportunities to provide greater clarity. The results were thoroughly discussed with plenty of insight and direction for future work, however the abstract could more concisely summarise the key findings of the study. Please also check the tenses throughout the document but primarily in the methodology where past and present tenses switch frequently.
Specific Comments:
- There were a few sentences in the abstract which I found myself reading a few times to understand, they may benefit from rewording to make reading flow better:
- ‘The initial microstructure and ice properties fed the model, which can reproduce the exact same test numerically’
- ‘When the contact law is adjusted’…what from? This is the first mention of the contact law
- It's already been stated that it reasonably reproduces the measured values – quantitively what is the difference between reasonable and good?
- Last sentence of abstract – how? What is meant by ‘better’?
- Overall I think that the discussion and conclusion read very well, but I’m not sure that the abstract summarises the key points clearly.
- Section 2.2.2 - A figure may be well suited to demonstrating the parameters of the interaction model – could be combined with Figure 1 for example.
- Figure 1 – The black lines used to represent cohesive interactions in the zoomed window are not easily visible. I wonder if using a different colour would make this more clear.
- Line 267 – what is the implication of choosing different weightings for the mean macroscopic force error and justification for choosing a factor of 2? i.e could different weightings result in selecting different combinations of mechanical parameters for the model comparison and is a better fit available?
- With reference to line 303, it’s not conclusive from the plots presented in S8 (and S18) that the depth hoar necessarily follows the same observed behaviour.
- Wrt line 309, as discussed in S2.1.2 the depth hoar seem to differ slightly
- Section 3.3 – in general, using percentages or factors rather than quantitative descriptions (eg ‘slightly over/underestimated’ / ‘agree fairly well’) to compare results is much more helpful in demonstrating the comparison. A mixture of these approaches is currently used.
Minor comments
- Line 50 – ‘measure’ – we should probably say we derive mechanical properties from cone penetration rather than measuring them
- Line 61 – typo ‘along on snow’
- Line 80 – typo ‘despite the NHPP’
- Line 96 – typo ‘failures mode’
- Suggest the title of Section 2.1 is adjusted to indicate this methodology refers to defining measured values of the microstructure. I’d attribute ‘experiments’ to the wider task of comparing test data to modelled outputs.
- Throughout the text, the term ‘experimental’ seems to be used to mean ‘measured’
- Line 140 – resisting force applied to the cone not the rod.
- Line 126 – we later refer to the sample depths in terms of mm. May be best to change 2 cm to 20 mm for continuity.
- Table 1 – put units for density and SSA on a separate line so they’re not split over 2 lines
- Line 204 – typo ‘clumps’ to become ‘clump’
- Table 2 – with reference to the Cohesion parameter default value (1.0 x 10^6), a value of 2.0 x 10^6 seems to have been fixed in sensitivity studies (eg caption of Figure 4, S12 etc), please confirm if default value is 1.0 or 2.0 x 10^6?
- Figures 2, 4, 6 – Force / Depth profiles could do with adjusting the x axis, removing dead space to better display data and to make trends more observable.
- Line 347 – figure reference should be to fig 5?
- Line 453 – I think the values stated for DZ obtained from CT scans refer to RG, RGlr and DH respectively, but without the PP samples would be helpful to restate these for clarity.
- Line 564 – typo – delete ‘and’
Citation: https://doi.org/10.5194/tc-2023-30-RC1 - There were a few sentences in the abstract which I found myself reading a few times to understand, they may benefit from rewording to make reading flow better:
- RC2: 'Comment on tc-2023-30', Henning Löwe, 21 Jun 2023
Clémence Herny et al.
Clémence Herny et al.
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