(State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Provence and the Ministry of Science and Technology，Shandong University of Science and Technology，Qingdao，Shandong 266590，China)
Abstract：In order to study the mechanical characteristics and progressive failure mechanism of the roof-coal pillar structure，uniaxial compression tests were carried out to five groups of sandstone roof-coal pillar structure bodies with different height ratios. The acoustic emission(AE) monitoring technique and the digital video camera system were used to investigate the failure process of the structure. The structural strength of the structure is the combined strength of sandstone，coal and interface. The contact frictional effects enhance the strength of coal in the interface，but weaken the strength of sandstone in the interface. With the decrease of the height ratio of sandstone to coal，the macroscopic failure initiation strength，the uniaxial compressive strength and the elastic modulus of the structure body reduce gradually. Under the same conditions，the more developed the primary cracks in the coal is，the lower the macroscopic failure initiation strength，the uniaxial compressive strength and the elastic modulus of the structure body are. The macroscopic failure initiation of the structure body causes the occurrence of the turning points on the stress-strain curves while the AE energy index reaches a peak value. After the macroscopic failure initiation，the AE energy index drops to the original level. Generally，the macroscopic failure initiations are located in the coal. When the height ratio of sandstone to coal is 9∶1，however，the macroscopic failure initiation occurs firstly at the interface. The propagation and coalescence of cracks in coal make the coal more broken and the local damage occurs in the coal. The coalescence of the local damages leads to the coal failure finally. The sandstone failure is caused by the crack propagation in coal cross to the sandstone interior. Due to the difference of the propagation ability，velocity and angle of cracks in the coal，the sandstones display the split failure，shear failure or no damage. With the increase of the height ratio of sandstone to coal，the degree of damage of the coal body and sandstone increases，and the coal body is broken more.
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2017, Vol. 36 
