Ramulu, M. (2012) Rock Mass Damage Due to Repeated Blast Loading at a powerhouse Foundation of Jurala Hydroelectric Power Project. Indian Mining & Engineering Journal , 51 (2). pp. 16-23. ISSN 0019-5944

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Abstract

Blasting produces seismic waves similar to those produced by earthquakes, but with relatively high frequency and low amplitude and the degree of structural damage depends on the total energy of explosion, distance from the source, and the character of the medium. 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 repeated blast induced dynamic forces on jointed rock mass. This paper deals with the research work carried out at Priyadarshini Jurala Hydroelectric Power Project (PJHPP) 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 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 vibrations when the blast is occurring relatively farther distances. The near-field damage was assessed by monitoring blast vibrations, borehole camera survey and ultrasonic testing of core samples taken from the test site. The far-field damage was assessed by continuous monitoring of vibrations, borehole camera survey and P-wave velocity of the rock mass before and after the repeated blasting. Borehole camera was used to examine the extent of damage in the rock mass. The study reveals that repeated dynamic loading imparted on the jointed rock mass from subsequent blast, in the vicinity, resulted in damage even at 20% of critical peak particle velocity (Vmax). The far-field damage due to the repeated blast loading of 50-75 cycles was more than 50%of the near-field damage. The blast induced damage was batter correlated with shear wave velocity rather than compressional wave velocity. 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/on jointed rock mass, when exposed to the repeated blast loading. The paper stresses the need for consideration of the effect of repeated blast loading in fixing the threshold limits of Vmax to avoid both near field and far-field damage.

Item Type:	Article
Subjects:	Blasting
Divisions:	UNSPECIFIED
Depositing User:	Dr. Satyendra Kumar Singh
Date Deposited:	10 Feb 2012 11:49
Last Modified:	10 Feb 2012 11:49
URI:	http://cimfr.csircentral.net/id/eprint/903

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