COMPARATIVE ANALYSIS OF BLAST-INDUCED VIBRATIONS IN SELECTED DOLOMITIC AND CALCITIC GNEISS ROCKS IN IGARRA AREA, EDO STATE NIGERIA

Abstract

The dissipated energy generated during blasting creates environmental problems in the form of ground vibration, air overpressure and flyrock. With increasing mining and construction activities in areas close to human settlements, ground vibration has become a critical environmental issue as it can cause human agitation and structural damage. Thus, it is necessary to determine the nature of wave’s propagation in different rock formations and establish criteria for reducing ground vibrations for each of these formations based on the geological conditions of selected locations. Octopus and Geowork quarries in Igarra area, Edo State were selected for study in calcitic gneiss and dolomite rock formations respectively. The magnitude of ground vibration was measured in term of Peak Particle Velocity (PPV) with the aid of USS 2000-DK Seismograph. Regression model by Pal and Brahama (2010), developed from United States Bureau of Mines (USBM) ground vibration predictor equation [PPV = K (SD) m] was used to predict PPV for the selected rocks with the aid of the ORIGIN computer software. The Scaled Distance (SD) of each measuring point was calculated. The energy transfer coefficient K, and site geological factor m, were determined for both rock formations. Analysis of the data collected for the twenty blasting activities in each of the quarry sites shows that the peak particle velocities (PPV) varied directly with the charge weight per delay (Q) but inversely with scaled distance (SD) and shot to monitored distance (D) for both selected dolomite and calcitic gneiss rock. The magnitude of vibration for dolomite was found to be about twice that of calcitic gneiss at 300m from the shot point and increased to about five times at 2200m. The main mechanisms which contribute to ground motion dissipation are damping, discontinuities, internal friction and geometrical spreading of rock.