Publisher's Synopsis
This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1910 edition. Excerpt: ...level of the tops of the subs, and is commonly known as 'stripping.' Consider that the work of stripping has reached the point shown in the longitudinal section, Fig. 43. By knocking down the supporting posts, as shown at the left of the first sub, the back of ore will fall and can be shoveled up and hauled away to the chutes. The settlement of the broken rock above is controlled by the mat of timbers which is constantly being added to by the timbers in the subs that are lost and broken. The method of cutting-out the pillars is shown in the plan, Fig. 43, as at the left where the stubs of pillars are being removed, the back standing on posts. As a sub cannot be worked beneath others not yet removed, it is necessary to either entirely remove the upper sub before beginning work on a lower one, or to carry on the stripping in descending order, each sub being carried some distance in advance of the one below. As soon as the stripping operation reaches a main level that level is abandoned and all communication with the subs below must be through the lower level. The usual practice is to have one level or lift (the block of ore between levels) in the process of stripping; the next lower subdrifting, while the third lift below is being opened up by cross-cuts. The ore will also have to be run through the chutes from the upper to the lower sub. In order to facilitate the handling of timber it is brought in from the upper level and lowered to the respective subs instead of being raised as in the top-slice method. Light but close timbering is the rule and by careful work the caving ground can be controlled with little or no danger of crushes and loss of ore. The work of mining by the sub-drift method as described is for comparatively hard and...
