Ramulu, M. and Choudhury , P.B. and Raina, A.K. and Chakraborty, A.K. (2009) Effect of Repeated Blast Vibrations on Rock Mass Damage at a Penstock Tunnel of a Hydroelectric Power Project - A Case Study. Journal of Rock Mechanics and Tunnelling Technology , 15 (1). pp. 17-36. ISSN 0971-9059

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Abstract

The detonation of explosive charges releases quantities of energy that can produce rock and soil deformations in the vicinity of blasting site. Extensive data are available on blasting in general and 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 underground structures like tunnels and caverns. This paper deals with the research work carried out at Koldam Hydroelectric Power Construction Project (KHEEP) on the effect of repeated blast vibrations on the joined rock mass. Multiple rounds of blasts were conducted at the penstock tunnels and at the excavation site for powerhouse foundation. The damage caused by blast induced vibration can be categorized into two types: (i) near-field damage due to high frequency vibrations when the blast is occurring in the close proximity and (ii) far-field damage due to low frequency vibration when the blast is occurring in the close proximity and (ii) far-field damage due to low frequency vibrations when the blast is occurring relatively at farther distance. The near-field damage was assessed by Holmberg-Person model by means of monitoring ground vibrations and by borehole camera inspection surveys. The far-field damage was assessed by measuring deformations of borehole extensometers and by borehole camera inspection surveys. Peak particle velocities (Vmax) generated by blast rounds were recorded by installing triaxial geophones near the borehole extensometers and borehole camera inspection holes. Damage assessment instrumentation was carried out at both the sides of penstock tunnel was as another objective of the study was to compare the extent of rock mass damage with different joint orientations. The study reveals that repeated dynamic loading imparted on the jointed rock mass from the subsequent blast, in the vicinity, resulted in damage even at 22-26% of critical peak particle velocity (Vcr). The far-field damage due to the repeated blast loading, after 36-42 rounds, was more than 70% of the near-field damage. The results of the study indicate that vibration levels, even at less than critical Vmax, can cause safety and stability problems to the structures in jointed rock mass, when exposed to the repeated blast loading. The paper stresses the need for consideration of the effect of repeated blast loading. The paper stresses the need for consideration of the effect of repeated blast loading for fixing the threshold limits of Vmax to avoid the blast induced damage.

Item Type:	Article
Uncontrolled Keywords:	Tunnelling; Repeated balsting ; Rock masss damage; peak particle velocity
Subjects:	Blasting
Divisions:	UNSPECIFIED
Depositing User:	Dr. Satyendra Kumar Singh
Date Deposited:	07 Jan 2012 07:17
Last Modified:	07 Jan 2012 07:17
URI:	http://cimfr.csircentral.net/id/eprint/606

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