Study on Mine Strata Behavior Law of Combined Mining in Ultra Contiguous Seams

In order to obtain mine strata behavior law of combined mining face in ultra contiguous seams under different coal mining techniques, the site measuring method was applied to mine strata pressure observation on a coal mining face in seams with a displaced distance of 20 m between the upper seam and the lower seam. The observation results showed that due to the upper seam had a low mining height and a hard roof, which led to there was no obvious primary roof weighting and no p eriodical roof weighting, an advance influence serious scope of the roof weighting was 20 m in front of the coal mining face and a depth of the plastic zone in the gatew ay of the coal mining face was 1. 5 ~ 2.0 m. A primary roof weighting and average periodical roof weighting of the coal mining face in the lower seam was 27.4 m and1 5.5 m in step individually, an advance influence serious scope of the roof weighting was 30 m in front of the coal mining face and a depth of the plastic zone in the gate way of the coal mining face was 2 m. Thus under above conditions, a displaced distance of 20 m was irational.