Ensuring the Safety of Multistoried Residential Structures during Excavation of Hard Rock with Controlled Blasting Operations: A Study

Blasting is the most suitable and preferred method for excavation of hard rock material near existing civil structures. Uncontrolled use of explosives during blasting can lead to various unwanted effects that have the potential to damage the structures present in the close proximity. However, by adopting the methodology of controlled blasting these adverse effects can be minimized and restricted within the acceptable limit. Among the unwanted effects, high amplitude ground vibration is the most destructive in nature, and, hence, maximum attention is given to control the amplitude of blast induced vibrations. Therefore, limiting the intensity of ground vibration within the permissible range is very much essential for safely carrying out the excavation work near important existing civil structures. In this research work, controlled blast study has been conducted for rock excavation in close proximity of the newly constructed residential structures located in urban areas of Mumbai, Maharashtra, India. Twelve (12) trial blasts have been carried out at the actual site of excavation for optimization of various blast design parameters. The ground vibrations generated by trial blasts were monitored at various distances in close proximity of the buildings, and underlying rock strata. Blast induced ground vibration data collected from all the trial blasts have been used for development of a site-specific attenuation relation, which has been further utilized to estimate safe charge weight per delay for use during the actual hard rock excavation. The hard rock excavation has been successfully carried out without inducing any physical damage in the neighboring residential structures by using the recommended safe charge weight per delay.