Verma, H.K. and Dwivedi, R.D. and Pal, Roy P. and Singh, P.K. (2016) Causes, impact and control of overbreak in underground excavations. In: Recent Advances in Rock Engineering (RARE 2016), 16-18, Novermber, 2016, Bengaluru, India.

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Drilling and blasting has been a preferred method of rock excavation world-wide. Blasting inevitably causes damage to the peripheral rock mass, which culminates in the form of overbreak and damaged zone. Damage or overbreak not only endangers the safety of structure and cost escalation but also delayed completion. Too large damage zone endangers the safety of the front line workers due to reduction of stand-up time especially for poor rock mass. Functionality and postconstruction performance of structures get affected due to large extent of damage zone, if not taken care in time. Field investigations were carried out at five different Himalayan tunnels to formulate an empirical equation for predicting blastinduced overbreak for wide range of rock mass quality wherein Q values ranged between 0.03 and 17.8. The proposed equation involves parameters like specific charge, perimeter charge factor, maximum charge per delay, rock mass quality (Q), advancement and confinement factors. These parameters are readily available at the site without any difficulty. Nearly 113 experimental blasts were monitored and data so collected were used to formulate an index termed as scale effect (Si), which is the ratio of tunnel crosssectional area and block size of rock mass. It is revealed that when Si becomes greater than 4, the range of overbreak lied between 8 and 25%.

Item Type: Conference or Workshop Item (Paper)
Uncontrolled Keywords: rock mass damage; blasting; overbreak; Maximum charge per delay; scale effect
Subjects: Blasting
Depositing User: Mr. B. R. Panduranga
Date Deposited: 10 Aug 2017 05:38
Last Modified: 10 Aug 2017 05:38

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