3.3.1 Shotcreting Video

3.3 Primary Shotcrete protection

•The primary stabilisation of the tunnel excavation is achieved by shotcrete.

•The shotcrete stabilises the excavated rock surface by filling the cracks produced in the rocks

•Primary shotcrete consists of M40A10 grade concrete. The shotcrete is sprayed throughout the excavation with the help of a computer operated machine called MYCO POTENZA.

•Along with shotcrete, an accelerator admixture is pumped so as to harden the shotcrete concrete immediately.

•If accelerator is not used, the shotcrete may not stick to the excavated surface.

•The accelerator commonly used is Sodium Silicate.

•The quantity of accelerator is kept 7% of the volume of shotcrete.

MYCO potenza for Shotcreting

3.2 De-fuming, Mucking and Scaling

• It takes about 30 minutes to expel the fumes out of the tunnel. All the workers and engineers are supposed to move out of the tunnel during this process.
• After De-fuming, mucking operation starts. Mucking is the operation of removing the blasted rock from the tunnel face.
• In Rohtang tunnel, a conveyor belt is used to convey the Muck out of the tunnel. The conveyor mechanism has been installed by ROWA Tunneling Logistics.
• The facilities are designed in such a manner, so that muck volume of 600 tons per hour can be effected.
• The removal of loose rock which has not been removed during blast is called as Scaling. Usually this operation is done using Hydraulic hammer.
  
   
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3.1 Drilling and blasting

•The face of the tunnel is made smooth with the help of hydraulic hammers.

•Holes of diameter 48mm to 51mm are drilled on the face of top heading or benching with the help of a machine called Boomer.

•The maximum length of the hole is kept 3m.

•The holes are filled with explosives and connected to a non electric detonator. The detonating mechanism is placed at least 500m distance from blast site.

•The detonator used for explosion is a non electric detonator and is commonly called as Shock Tube Initiator.

Boomer for hole drilling

Cortex tube for detonation purpose

Explosive