Smooth wall blasting is the most commonly used underground technique and was developed in Sweden (The Blasters’ Handbook, n.d.). The smooth wall line technique is composed around the final excavation line under ground where the holes are lightly loaded to reduce the amount of overbreak. These explosives are also decoupled from the sides of the borehole.
The smooth wall holes are started after the initial blast, which is the last characteristic of smooth wall blasting. Before blast damage starts, smooth wall blasting will enable it to spread past the smooth wall line.
In order to provide a smooth pro file for the perimeter, the most damaged rock will be removed from the last excavation line. The holes should be shot in groups to optimise the charge per delay if more smooth wall holes are needed than can be started in an 8 ms time period.
Compared to presplit blasting operations, smooth wall blasting may require a wider bore hole spacing. For smooth wall blasting, a burden-to-spacing ratio of 1.5:1 is usually the starting point. Occasionally, a pilot heading is employed to guarantee the rock’s maximum relief.
A tiny tunnel that is dug in the middle or close to the top of the planned tunnel is called a pilot heading. The cross-section is drilled and shot once the pilot heading has been fully dug. As a result, a larger section of the excavation line can be blasted smoothly.
The smooth wall technique also involves more perimeter drill holes when compared to conventional underground methods. Drilling costs have the greatest impact on the economics of any blasting operation (The Blasters’ Handbook, n.d.).
Additionally, smooth wall blasting is known to have performance issues in weak rock formations (The Blasters’ Handbook, n.d.).
If the rock mass is too weak to support itself, the smooth wall blast will not eliminate the need for additional support (Eades & Perry, 2019). Drilling accuracy is a paramount concern with smooth wall blasting. Due to the additional challenges of drilling and blasting in an underground heading, drill accuracy is critical to the success of a smooth wall blast (Eades & Perry, 2019).
When the smooth wall holes cannot all be fired on a single delay, the relief is limited to the arch and partially down the rib because of the muckpile. Therefore, smooth blasting results will degrade further down the rib of the excavation line, which may cause safety concerns in larger entries (Eades & Perry, 2019).
Reference
Eades, R. Q., & Perry, K. (2019). Understanding the connection between blasting and highwall stability. International Journal of Mining Science and Technology, 29(1), 99–103. https://doi.org/10.1016/j.ijmst.2018.11.016
The Blasters’ Handbook. (n.d.). Isee.Org. Retrieved May 13, 2025, from https://isee.org/resources/publications/the-blasters-handbook
