Ramulu, M. and Raina, A.K. and Choudhury , P.B. and Chakraborty, A.K. (2009) Effect of repeated blast Vibrations on damage intensity of granitic rock mass at an hydroelectric Construction project. Journal of Mines, Metals & Fuels, 57 (5&6). pp. 148-155. ISSN 0022-2755

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Abstract

Rock blasting induced ground vibrations produce deformations in the vicinity of blasting site. The effect of blast loading on structures is a growing concern of safety and stability. Extensive data are available on the behavior of surface structures subjected to blast vibrations. However, only limited information is available on the effect of blast induced dynamic forces on the underground opening like tunnels and caverns. The reported findings state that blast induced dynamic stress, one or several cycle of repeated strains may cause deterioration in the rock mass or create damage to the dam foundation. This paper deals with the research work carried out at jurala hydroelectric power project (JHPP) on the effect of repeated blast vibrations on powerhouse foundation in a jointed rock mass. The damage caused by blast induced vibrations can be categorized in to two types: (i) near-field damage due to high frequency vibrations when blast is occurring in the close proximity and (ii) far-field damage due to low frequency vibrations when the blast is occurring relatively farther distance. The near-field damage was assessed by monitoring ballast vibrations and borehole camera inspection survey. The far field damage was assessed by continuous monitoring of vibrations, borehole camera inspection survey and P-wave velocity measurement by ultrasonic testing machine. Borehole camera was used to examine the crack extension and damage inspection of rock mass. This paper reveals that repeated dynamic loading imparted on the jointed rock mass from subsequent blast, in the vicinity, resulted in damage even at 22% of critical peak particle velocity (Vmax). The far-field damage due to the repeated blast loading of 40-45 rounds was more than 77% of he near-field damage. The results of the experimental study indicated that vibration levels, even at less than critical Vmax, can cause safety and stability problems to the structures in /on joined rock mass, when exposed to the repeated blast loading. This paper stresses the need for consideration of the effect of repeated blast loading in fixing the threshold limits of Vmax to avoid far-field damage.

Item Type:	Article
Subjects:	Blasting Rock Testing
Divisions:	UNSPECIFIED
Depositing User:	Dr. Satyendra Kumar Singh
Date Deposited:	17 Nov 2011 09:52
Last Modified:	26 Nov 2011 09:31
URI:	http://cimfr.csircentral.net/id/eprint/9

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