CHAPTER XI.
Methods of Supporting Excavation.
| TIMBERING; FILLING WITH WASTE; FILLING WITH BROKEN ORE; PILLARS OF ORE; ARTIFICIAL PILLARS; CAVING SYSTEM. |
Most stopes require support to be given to the walls and often to the ore itself. Where they do require support there are five principal methods of accomplishing it. The application of any particular method depends upon the dip, width of ore-body, character of the ore and walls, and cost of materials. The various systems are by:—
| 1. | Timbering. |
| 2. | Filling with waste. |
| 3. | Filling with broken ore subsequently withdrawn. |
| 4. | Pillars of ore. |
| 5. | Artificial pillars built of timbers and waste. |
| 6. | Caving. |
Timbering.—At one time timbering was the almost universal means of support in such excavations, but gradually various methods for the economical application of waste and ore itself have come forward, until timbering is fast becoming a secondary device. Aside from economy in working without it, the dangers of creeps, or crushing, and of fires are sufficient incentives to do away with wood as far as possible.
There are three principal systems of timber support to excavations,—by stulls, square-sets, and cribs.
Stulls are serviceable only where the deposit is so narrow that the opening can be bridged by single timbers between wall and wall (Figs. 28 and 43). This system can be applied to any dip and is most useful in narrow deposits where the walls are not too heavy. Stulls in inclined deposits are usually set at a slightly higher angle than that perpendicular to the walls, in order that the vertical pressure of the hanging wall will serve to tighten them in position. The "stull" system can, in inclined deposits, be further strengthened by building waste pillars against them, in which case the arrangement merges into the system of artificial pillars.
| Fig. 28.—Longitudinal section of stull-supported stope. |
| Fig. 29.—Longitudinal section showing square-set timbering. |