Analysis of Blast Pattern to Evaluate Extent and Causes of Overbreak in Large Cavern

Mandal, S.K and Singh, M.M. (2008) Analysis of Blast Pattern to Evaluate Extent and Causes of Overbreak in Large Cavern. Blasting and Fragmentation , 2 (1). pp. 1-26. ISSN 1937-6359

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Abstract

Damage is classified as loss in the integrity or deterioration in the quality of rock mass and is influenced by methodology of excavation on the geo-technical properties of rock mass. Overbreak, on the other hand, is the result of damage and is quantified in either of the terms viz., extra mucking, shot-creting, application of extra support system and extension of scheduled completion time. Damage or overbreak in rock mass by the impact of blasting, is generally unavoidable but, the magnitude can be minimized so that it does not deteriorate the quality or integrity of structure. The paper, here, analyses magnitude of overbreak of a powerhouse cavern with respect to different blast patterns implemented at the site. The magnitude of overbreak was analyzed in terms of profile measurement with the help of laser profiler and percentage of half-cast markings observed on the periphery rock wall. The paper revealed the impact of decoupling ratio, blast pattern and geometry of blasting patch on the magnitude of overbreak. The author observed that presence of un-favourable joint pattern or foliation plane along the periphery rock wall couldn’t contain magnitude of overbreak within allowable limit. The analyses revealed that percentage of half-cast markings on periphery rock wall was influenced by response of rock towards detonation of explosive and cannot be a single parameter to assess the effectiveness of a blast. The analyses also revealed that magnitude of overbreak for down-stream wall was more than that observed in up-stream wall.

Item Type:	Article
Subjects:	Blasting
Divisions:	UNSPECIFIED
Depositing User:	Dr. Satyendra Kumar Singh
Date Deposited:	21 Dec 2011 05:40
Last Modified:	21 Dec 2011 05:40
URI:	http://cimfr.csircentral.net/id/eprint/433

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