Sublevel caving without bottom pillar is the method of mining used at Huashugou Mine, Jiuchun Iron and Steel Co.

The main target coal seam of Xieqiao Mine is directly covered with the Quaternary bottom gravels, whose impermeability affects the reasonable retainment of waterproof pillar.

This paper proposes a new working face ventilation system: top gas tunnel small pillar outside the bottom return air laneway layout, in other words, which is gas tunnel location evolution.