नाइट्रोजन के गुण || properties of nitrogen || gas testing video hindi || indianminerology
gas testing video #03
ADVANCING AND RETREATING LONGWALLS
ADVANCING AND RETREATING LONGWALLS:- Advancing Longwalls:- In this method, the face start point is close to the main headings, usually leaving a barrier pillar to protect them. Once the face equipment is installed, extraction commences working away from the main headings towards the block limit. Obviously the main and tailgates do not exist prior to the start of extraction and have to be formed at each end of the face as mining progresses. The gate roads are effectively in the goaf and a false rib has to be installed on one side, usually by constructing a small pillar, sometimes using stone cut from the roof in thin seams or using some type of cementitious material brought into the mine. Such gate roads tend to require a very heavy support system (yielding steel arches have often been used). Principle of advancing longwall Advancing longwalls were once common in Europe in relatively thin seams where packs were constructed using stone, which had ...
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