The Mumbai Metro Rail Corporation (MMRC) has revealed the first animated look of how controlled blasting is done and what exactly is controlled blasting.
While controlled blasting is going to be carried out in the city for underground Metro Station construction of Colaba-Bandra-Seepz Metro-3 corridor, the Mumbai Metro Rail Corporation (MMRC) has revealed the first animated look of how controlled blasting is done and what exactly is controlled blasting.
MMRC in its monthly magazine for November 2017 has explained about why and how the activity of controlled blasting is carried out. Blasting is carried out for hard rock excavation and is common in several civil engineering projects like tunnels, canals, pipeline projects, hydel power projects and port.
It has in the past said that at several locations where the shafts for Metro-3 are located and controlled blasting would be conducted includes Colaba, Azad Maidan, Andheri, and Mahim. The tunnelling for Metro-3 will be done 20 to 25 metres below the ground for excavating rocks using 17 tunnel boring machines (TBMs).
The MMRC in its monthly magazine for November 2017, said, "The excavation of soil or rock for station and tunnel construction works can be done either by TBMs or by blasting the unit quantity of rock. If the rock is very hard and abrasive in nature, the mechanized excavation takes longer time due to increase in the down time for replacement of cutting tools and parts in the machines."
"Hence, to conserve the time required for tunnelling, controlled blasting methods are preferred over conventional mechanized method of excavation, the MMRC said.
Permissions for blasting:
Controlled blasting can be carried out only after receiving statutory permissions, such as - Police department NOC - after scrutiny of safety and security of the premises.
Permission from Petroleum and Explosives Safety Organization (PESO) {formerly known as Department of explosives} obtained on verification of the credentials of the company executing the blasting operations.
Process of controlled blasting:
Transfer of explosion energy to the rock is a function of both the characteristics of explosives used and the characteristics of ground/rock strata.
When the charge and blast diameter are almost equal, shock pressure delivered to the sides are maximum. If the charge diameter is less than blast hole diameter then this shock pressure on the sides will decrease exponentially.
This principle is used in the design of blast to reduce the over-break. In controlled blasting, Muffling (process of covering blast holes properly before blasting) is carried out to prevent fly rock (debris which is ejected through air by explosive blast).
Meanwhile, the construction of Colaba-Bandra-Seepz Metro 3 corridor started in October 2016 and it is a crucial connectivity point between north and south Mumbai. It expected to be completed by 2021.
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