ABSTRACT

Blasting operation nearby the dwelling areas often needs precaution to the surrounding structures from blast-induced ground vibration, flyrock and air overpressure. More attention and special cares are required when blasting is to be carried out in sensitive and hilly areas. In this paper, a successful controlled blasting in one of the most sensitive areas at Durtlang-Leitan has been discussed in detail. Durtlang-Leitan is a through-cutting road, constructed on the hill slope. It is located in Durtlang area, the southern part of Aizawl city, which is the capital of Mizoram State, India. Residential structures and important office buildings are located in close proximity of the through cutting road. To obtain a stable excavated slope, smooth wall blasting technique was used. Smaller blasthole diameter of 32 mm was selected for better control on ground vibration and flyrock. Safe explosive charge weight per delay was determined by monitoring ground vibration and air overpressure with modern seismographs. Muffling arrangement was also done for complete control on flyrock. The project was successfully completed with proper blast design and careful monitoring of the total drilling and blasting operations.

1. INTRODUCTION

The term 'controlled blasting' has two senses of meaning and applications. In one sense, controlled blasting means controlling of ground vibration, flyrock and air overpressure (noise) within safe limit. On the other hand, controlled blasting means minimization of over break beyond the boundary of the excavation area. The first one is generally applied when blasting operation is to be conducted near residential structures/buildings or other sensitive environment. The ater is applied both in surface as well as underground to obtain smooth and stable final excavation wall. Proper selection of blast design parameters and systematic blasting operation is crucial for both the controlled blasting operations. Blasting operation close to the residential areas often requires control of ground vibration, flyrock and air overpressure. Ground vibration generated from blasting may produce structural damages to nearby residential houses. When an explosive charge inside the blasthole is detonated, beyond the perimeter of damage rock zone, the pulses are generated which are called as seismic waves or elastic waves. Seismic waves generated from blasting source travel in all directions. As they travel through the medium, they cause particle of the medium in motion which is called vibration. The velocity of a particle at any instant of time during the vibration disturbance is called as particle velocity. The maximum velocity from the position of rest is peak particle velocity or in short ?PPV?. PPV has traditionally been used as a means to establish the degree of blast damage [1, 2]. The principal factors that affect ground vibration are maximum charge weight per delay, distance from the blast, delay period used and the blast geometry. Spatial distribution of explosive charge also affects the characters and intensity of ground vibration [3]. The other factors that affect vibration intensity are confinement, physical properties of the rock, coupling, component scatter of detonating devices, time of energy release and type of explosive.

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