Week 4 Tunnelling & TBM Course: Drill & Blast

Week 4 (10th Feb '14 to 14th Feb '14) of 2nd Level specializing course in Tunnelling and TBM was mostly dedicated to Drill & Blast methods. The cycle of operation in Tunnelling during Drill and Blast (Viz, Blasting scheme preparation, Drilling, Charging, Blasting, Scaling and Mucking) was discussed one by one. 

D and B Cycle [1]

A brief idea about the evolution of explosives from Black powder --> Nitroglycerin based explosives (1st generation) --> TNT based explosives (2nd generation) --> Emulsion based explosives (3rd generation) was discussed. Different applications of the above explosives for specific conditions are studied.

• Nitroglycerin based explosives (1st generation) include: Dynamex, Gurit (used for contour blasting), Primex, 
• TNT based explosives (2nd generation) include: Watergel explosives, ANFO
• Emulsion based explosives (3rd generation) include: Emulite, 

Details of Initiation device / Detonators was discussed with emphasis on the NONEL detonator. Electric detonators are divided into:

• Instantaneous detonators - Used for stone and boulder blasting, presplitting etc.
• Milli-second detonators (less than 100 ms) - Used for bench and trench blasting
• Half-second detonators (500ms) - Are used when longer delays are required to prepare space for the movement of blasted rock mass.

NONEL is similar to electric detonators but it is immune to any electric hazard. It is based on shock wave instead of an electric pulse hence, fuse wires and legwires are replaced by plastic tubes (~3mm dia).

Two main schemes of Cut Types were discussed in detail:

• Parallel holes cut: Used for narrow tunnels but can be used for large tunnels also. Consumes more explosives for the initial cut 
• Inclined holes cut: Used in large excavation cross section

Different building codes are studied for the allowable vibration level and the methods adopted to control the vibrations were discussed.

Guidelines for Allowable Vibration - Swedish Standard [3]

The lectures were followed by an exercise on the design of the Blasting round for both the cut types mentioned above and the design of charging volume  for vibration control based on a practical example (more details later).

References:
[1] Heiniö, Matti. Rock excavation handbook for civil engineering. Sandvik, Tamrock, 1999.
[2] Olofsson, Stig O. Applied explosives technology for construction and mining. Applex, 1990.
[3] Persson, Per-Anders, Roger Holmberg, and Jaimin Lee. Rock blasting and explosives engineering. CRC press, 1993.
[4*] Johansen, John, and C. F. Mathiesen. Modern trends in tunnelling and blast design. CRC Press, 2000.