Print8.4.1b Square Set Stoping
This mining method was used to mine in the weakest of rock masses. It is extremely expensive, and you’ll see why in a moment, but was used to recover silver and gold deposits through the 1970s in the U.S. The concept of the method is simple: we will mine only a small volume and immediately build and place timbers into the opening to support it on all sides. The timbers will be precisely cut and fitted to form a cuboid. This process will continue indefinitely, resulting in mines with thousands of these square sets. The dimensions of the square set will vary, but 6’x6’x8’ would be illustrative. Take a look at this figure, which illustrates a small portion of a mine with the square sets. The timbers are large, at least 6” square and likely between 8”- 12” or larger. The cost of acquiring such timbers today would be cost prohibitive, but that cost would be small compared to the labor cost to build these square sets. Elaborate and precise joinery was required so that the strength of the square set as not compromised. Today it is difficult to find carpenters with the skill to construct such precise joints! Note in the figure the use of the lagging to keep the weak ground from flowing into the area supported by the square sets.
