Yade

Modeling fractured rocks

Asked by hala El Fil

Dear,

I have an inquiry regarding modeling a fractured rock specimen, based on Scholtes et al. (2012) the fractured rock specimen is modeled by adding a discrete fracture network to the discrete element model of the intact material. I wanted to ask for further clarifications regarding the following issues:

1. How are the microproperties calibrated to match the macroproperties of the specimen?

2. In the Scholtes et al. (2012) paper, they backed up their microproperties by matching them to the macroproperties obtained using a triaxial test, is that test enough? Having almost 6-7 microproperties that are matched with only 3 macroproperties is enough? If yes could you please justify it? And if not, are there other methods that could be used to match micro-macro properties of the material being modeled?

3. In the same paper as well, a biaxial test was modeled on the fractured specimen, I am still a beginner in Yade, so could anyone please explain how the loading was performed? Is the specimen first normally load then shear until failure? Is the code available?

Thank you so much

Best Regards,
Hala El Fil

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Luc Scholtès (luc) said : 		#1

Hello,

Here are some answers:

1) and 2):

calibration of DEM models is a difficult task if you want it to be relevant. Many DEM/BPM users often underestimate the calibration process which has to be done considering as much loading paths as possible:

- uniaxial tension test -> elastic properties and uniaxial tensile strength (some people might want to simulate brazilian tests so as to compare directly with lab experiments)
- uniaxial compression test -> elastic properties (must be the same as in uniaxial tension) and uniaxial compressive strength
- triaxial compression tests at several confining pressure -> failure envelope

Please have a look at [1] where a calibration procedure is explained (I insist on the fact that this is A calibration procedure and not THE calibration procedure). Also, you will see in that paper that every microproperty of the JCFPM are related to given macroscopic properties. Of course, as usual for DEM model, it is a matter of trials and errors to identify the right set of microproperties. There is no direct mathematical relationship between micro and macro properties (unless you work with regular packings...).

3) I don't remember performing a biaxial test for that paper... I remember performing a uniaxial compressive test on a sample with a pre-existing crack and a direct shear test on a sample with several pre-existing cracks. I guess you are referring to the direct shear test. The procedure is exactly the same that you would use in the lab: normal loading through top moving plate and bottom fixed plate and then, after reaching the desired normal load, shearing with the help of lateral walls (Casagrande box type). Please have a look at this thread:

https://<email address hidden>/msg05815.html

Luc

- [1]: Scholtès, L., Donzé, F.V. (2013), A DEM model for soft and hard rocks: role of grain interlocking on strength. Journal of the Mechanics and Physics of Solids (61), pages 352–369.

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