Are there some equations or cases study about the relation of overbreak in tunnels related to Stress condition and joint discontinuities? I read about Barton & Grimstad (2014) article and they said that "If a rock mass has characteristics such as Jn = 9 (three joint sets) and Jr = 1 or 1.5 (smooth planar or rough planar joints), there may be sufficient risk of overbreak that the economy of the project is affected.".
What do you think about it, or could you provide some case analysis of this?
Regards
Many published articles pertaining to this issue in the RETC semi-annual conference proceedings.
The effect of joints on overbreak has been discussed with case history in the following publication:
Singh, S.P.,2001. The influence of geology on blast damage. CIM Bulletin, Vo. 94, No. 1048, March 2001, pp.121-127.
The effect of joints on overbreak and control measures have been discussed in the following publication:
Singh, S.P. 2005. Blast damage control in jointed rock mass. Fragblast Journal, Vol. 9, No. 3, September 2005, pp.175-187.
This paper also discusses the critical particle velocity for minor and major damage based upon rock mass rating.
you can find it in Gotthard tunnel, Jinping 2 tunnel, Hallandsas tunnel and wienerwald tunnel conditions. some papers related to difficult geological condition in "Rapid excavation and tunneling proceeding" could be useful.
overbreaks in underground excavations such as tunnels, mines and etc.. are absolutely affected by joint condition, stress condition , geological formation..
It's better to use finite element or/and finite difference software to solve your problem.
There are a number of authors who've studied this. Below are a few papers I found by doing a casual search in Google Scholar; hence, this is by no means the only ones. I'd suggest searching for more publications from these authors, as well as in the Tunneling and Underground Space Technology journal. Although most of them relate overbreak to blasting, you might find some charts or formulae in there that might be of help. Regards, Shahé
- Causes, impact and control of overbreak in underground excavations. SP Singh and P Xavier (2005): Tun Und Sp Tech.
- Evaluating extent and causes of overbreak in tunnels. SK Mandal and MM Singh (2009): Tun Und Sp Tech
- Assessment of geological overbreak for tunnel design and contractual claims. MA Mahtab, K Rossler, GS Kalamaras, and P Grasso (1997): Int J Rock Mech Min Sci.
- Assessing the effects of joint orientation and rock mass quality on fragmentation and overbreak in tunnel blasting. AK Chakraborty, JL Jethwa, and AG Palthankar (1994): Tun Und Sp Tech.
- Effects of joint orientation and rock mass quality on tunnel blasting. AK Chakraborty, JL Jethwa, and AG Palthankar (1994): Eng Geol.
- Prediction of blast-induced overbreak from uncontrolled burn-cut blasting in tunnels driven through medium rock class. K Dey and VMSR Murthy (2012): Tun Und Sp Tech.
- On the influence of rock mass quality on the quality of blasting work in tunnel driving. N Innaurato, R Mancini, and M Cardu (1998): Tun Und Sp Tech.
Standard structural mapping and wedge analysis of data should provide an inkling but many factors at play including in-situ stress, size of tunnel, excavation method, etc.
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