Drill And Blast Tunneling

Published: May 24, 2017 | Last updated: July 5, 2023

What Does Drill And Blast Tunneling Mean?

Drill and blast tunneling is a method of excavation involving the controlled use of explosives to break rock. It was the primary means of tunneling through rock prior to the advent of tunnel boring machines. Like trenchless construction and horizontal directional drilling, drill and blast tunneling is a form of subsurface construction. But large-diameter tunneling, like that performed by drill-and-blast or tunnel boring machines, is generally considered separate from trenchless technology.


Trenchlesspedia Explains Drill And Blast Tunneling

Drill and blast tunneling continues to be used despite the prevalence of tunnel boring machines. It may be more economical in shorter tunnels where the cost of a tunnel boring machine may be prohibitive. Significant advancements in blast technology, such as pumpable emulsion explosives, have also made it more attractive in some situations. The choice of tunneling method may vary from project to project.

This form of excavation became possible with the advent of gunpowder in the 1600s. But it was not until the invention of dynamite in 1867 that the drill-and-blast method found greater success. Today an advanced form of explosive called ANFO (ammonium nitrate/fuel oil) provides more safety for workers.

There are generally four steps to drill-and-blast. Gary S. Brierley, tunneling expert and president of Dr. Mole Inc., calls it the “drill-load-blast-muck” cycle. He writes in an April 2015 article for Tunnel Business Magazine that it was a method developed by Walter and Francis Shanley for the Hoosac Tunnel in Montreal. The process can be described as follows:

  • Holes are drilled into the rock.
  • The holes are then filled with explosives.
  • The rocks collapse following detonation.
  • Rubble is removed and the tunnel surface reinforced.

Modern drilling is directed by computer controls. Such advancements, along with improved blast methods, make drill-and-blast tunneling a viable alternative even today.


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