This historic excavation technique involves drilling and blasting the upper portion of a tunnel heading, known as the breast, before taking out the bottom section or bench. Crews used this sequential approach to maintain stability in the rock face and provide a natural working platform for the upper drills. While newer mechanized boring machines have largely replaced it, the method remains relevant for short, specialized rock cuts or subway expansions where heavy equipment cannot fit.
We had to breast down the first fifty feet of the adit because the rock was too fractured for the roadheader.
Older tunnel specs often reference breasting down to dictate exactly how the rock stresses should be relieved during the initial drive.
Also heard as
- heading and benching
Related terms
Cut and cover
A shallow tunneling method where a trench is excavated, roofed over, and buried.
Earthmoving
The process of excavating, transporting, and grading soil and rock to prepare a construction site.
Breakthrough
The moment when an excavation or tunnel connects with an adjacent void or the opposite heading.