当当读书
Scientific American Supplement, No. 810, July 11, 1891

Scientific American Supple…

Various
0
2.99 原价¥2 开通租阅权,免费读此书
评论 赠一得一 收藏 分享
此书籍暂不支持在移动端购买和阅读

内容简介

If, while driving, a patch of low grade ore is met with, it can be enriched by taking a higher class from another face, and so on. Any grade can be produced by means of this power of selection. Opinions have been expressed that this system of timbering is not secure, and that pressure from above would bring the whole structure down in ruins. But an opinion such as this is due to miscomprehension of the facts. If signs of weakening in the timbers become apparent, the remedy is very simple. Four or more of the uprights are lined with planks, and waste material is shot in from above, and a strong support is at once formed, or if signs of crushing are noticed, it is possible to go into the stope, break down ore, and at once relieve the weight."
展开
大家都在看换一批
大家都在看换一批
领取优惠券

温馨提示:

您已领取的礼券,请到【个人中心】-【资产】中查看。