User:Morgan Riley/Timbering

Timbering is the traditional method used in underground mining to shore-up tunnels, adits, levels, and stopes with timbers to support the walls and roofs, and thus prevent a cave-in.

Alternatives to timbering include leaving pillars standing in the existing rock and using waste as fill materials, and in some cases, the use of masonry.

Timbering does not have to be of wood, and may be of other materials such as steel. (Storm 1903, 34)

Engineering factors
A number of factors are used to determine the materials, method and use of timbering in a mine. Geological factors: moisture, shrink-swell, solidity/strength of surrounding material.

The use of wood itself dangers of fire, rotting, collapse, etc.

Factors of using treated wood to prevent rotting; (Walters 529-530) air currents, temperature, and humidity within the mine. (Storm 1-7)

The ability of wood to burn could also be an advantage in a military context. In the tactic of sapping, a tunnel was constructed underneath an enemy's defences (such as earthworks or a wall). The tunnel was then set fire, collapsing the structure above it.

Costs and recovery considerations: cost of wood versus ore. Estimates in 1911 and 1924 calculated that approximately 0.25 cubic feet of timber were required per ton of coal mined.(Walters 499).

Obtaining suitable wood in the American Old West could be challenging in desert areas with few trees. Likewise, as time progressed, many trees had already been heavily logged and were no longer economically available for mining use. (Storm 1909, 1-7). At the turn of the 20th century, Douglas fir (known then as Oregon pine or Douglas spruce), was the preferred timbering wood on the Pacific Coast of the United States. (Storm 1909, 1-7).

Steel timbers first used in Europe, and later applied in the United States.(Storm 1909, 34) Unlike with metal timbering, the creaking of wood timbers may serve as a warning of structural failure.(Walters 537-538)

Basic forms
The wooden timbers are cut and used in several basic forms and techniques:
 * Lagging: simple form of loosly spaced boards to hold up a loose ceiling.
 * Props: 523-24
 * Bars: long timbers, = (Walters 515-16)
 * Posts: larger versions of props, used to support bars (Walters 524-525)
 * Wedges: = (Walters 516=517)

Square-set timbering
The geology of the Comstock Lode, site of a major silver rush in the 1860s, presented problems to the then-existing forms of timbering. The lode was too wide for most techniques, while at the same time the surrounding minerals expanded. German immigrant Philip Deidesheimer solved the problem with the invention of square-set timbering. It consists of a system of modular connecting cubes, which could be used and built out to any size stope.

Construction and reclamation
The timbers used may be taken to the mine in a number of ways, depending on the direction of the mine. In horizontal drift mining, it may be brought in on a mine railway; in slope mining, riding down on the skip (a bucket ordinarily used for hauling ore up from the mine). (Storm 1901, 52)

reclamation (Walters 533)