Study on Surrounding Rock Failure Laws of Mining Lower Group Coal Seam in North China Coalfield

In order to prevent coal mine water hazards results from surrounding rock failure by mining lower coal in North China Coalfield, a numerical model was b uilt based on the numerical simulation software FLAC3D.Water inrush information was monitored during mining process based on the optical fiber grating sensor techno logy.Lower coal surrounding rock stress and failore rules were studied by comparing numerical simulation and monitoring results.This research showed that the first wei ghting distance of the test face was from 35 m to 40 m and the periodic weighting step distance was from 10 m to 20 m.The coal floor could be divided to three stress ar eas which was increased stress zone, decreased stress zone and recovery stress zone.The coal roof failure shape was a composition of two saddle-shaped zones alon g trend and tendency directions.Normal failure depth of test face coal floor was from 10 m to 12.5 m, and it could reach 22.5 m near open-off cut and stop line.The large failure depth near the final line was the main reason of the test face water inrush accident.