Mining-induced mechanics behavior in the deep mine with an over-kilometer depth

In China,the shallow mineral resources of the earth have been gradually exhausted. There are lots of engi- neering disasters in deep mining when mining at 1 000-2 000 m depths due to the unknown mechanism in deep min- ing-induced stress field. At the Ji15 -31030 mining face with an over-kilometer depth in Pingdingshan Coal Mine No. 12,the research was carried out to study the mining-induced stress evolution law with different mining speeds. The in- situ monitoring tests including bolt stress testing,borehole stress testing and fractures in borehole monitoring were also carried out to investigate the appearance law of mining-induced stress field. Results showed that the peak advanced abutment pressure increases alternately as the mining face advances and fluctuates around 85 MPa due to great depths when mining over 80 m. The stress concentration factor is 3. 3,which is higher than that at shallow mining face. Over- lying strata forms “three-zones” consisting of the caving zone,cracked zone and bent zone. Meanwhile,the peak ad- vanced abutment pressure increases as the mining speed increases gradually,and the distance between peak pressure position and mining face decreases correspondingly,and the longer the length of the rock formed by the main roof breaking is. Hydraulic support pressure increases periodically with mining face advances. The bolt stress increases first and then decreases due to stress redistribution and energy releasing under the influence of mining,which concludes that mining influenced range is about 85 m. Borehole stress increases in the mining influence range about 75 m from the mining face,and decreases slightly when entering the advanced abutment pressure reduction zone. Strong mining disturbance results in fractures developing continuously as mining face advances,and fractures develop into crisscross broken zone as developed upwards.