| Popis: |
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 annoyance and structural damage. The magnitude of ground movement was measured in term of Peak Particle Velocity (PPV) with the aid of USS 2000-DK Seismograph. Site constant K, and site geological factor m were determined for both quarries by plotting the log-log graph of the maximum PPV against scaled distance. The data collected for the twenty blasting activities in each of the quarry sites have shown that the peak particle velocities (PPV) recorded varied directly with the charge weight per delay but inversely with scaled distance (SD) and shot to monitored distance for both selected sedimentary and igneous rock. A comparative analysis between the results obtained for constant charge per delay of 1000 kg, and monitoring distance of 500 m, 750 m and 1000 m were carried out. The magnitude of vibration for limestone is about twice that of granite at 300 m from the shot point and increase to about five times at 2200 m. This is evident when considering the main mechanisms which contribute to ground motion dissipation such as; damping of ground vibrations which cause lower ground vibration frequencies with increasing distance, discontinuities causing reflection, refraction and diffraction, internal friction causing frequency dependent attenuation, which is greater for coarser grained rocks and geometrical spreading of rock. |
