Continuous Monitoring of Ground Vibrations and Noise
Ground vibrations are measured, as a practice, whenever they are of a concern. The degree of concern and necessity to measure ground vibrations varies from very high to medium or low. A great number of Coal/ Limestone mines/ Iron Ore Mines/ Quarries, in India, fall under a high concern zone since villages and other critical structures lie in the proximity and these are often prone to damages that occur as a result. Only Kudremukh Iron Ore Limited (KIOCL) monitored all its blasts for vibrations whether required or not.
Whenever ground vibrations are measured at a particular location, the blast frequency also needs to be considered for damage assessment. From the data obtained, it can be seen, that blasts with a higher frequency and higher vibrations are less damageable than the blasts with lower blast frequency and higher vibration readings or blasts with lower blast frequency and lower vibration readings. Apart from vibrations and blast frequency intensity, factors like the nature of structures (likely to be affected by the blasting), need to be understood for assessing damage. A concrete structure can withstand more vibrations than mudwalls.
Blasting is not the sole source of ground vibrations. Heavy duty truck movements, railway rake movements, aircraft landings, oscillating water in dam structures also generate a significant amount of vibrations which can prove to be devastating at times. On several occasions, vibrations from these sources that frequently occur are commonly ignored, can cause major damages to structures. Continuous vibrations as a result of these, also need to be considered for damage assessment and analysis. This highlights the need for the establishment of a system that takes into account all the vibrations occurring continuously.
We need systems which measure all vibrations constantly and continuously irrespective of its source, time of occurrence and intention to monitor. Only continuous monitoring of vibrations enables the project authority to contest or defend the blasting activities and provide sufficient proof that the damages resulted are due to these other sources of vibrations and not blasting damages indeed.