An innovative yielding prop with high stable load capacity and long shrinkage distance in coal mine

Conventional free standing supports, such as wooden cribs, hydraulic prop in coal mine and other underground engineering have some disadvantages, such as low stiffness for wooden cribs, costly, overweight and inconvenient for hydraulic prop, etc. This paper introduced a new yielding prop with high stable load capacity and long shrinkage distance, which is mainly consisted of an inner and outer prop and a circle of steel balls. The stable load capacity is generated by the plastic flow induced by the contact behavior among inner prop, steel balls and outer prop and the supporting height could be adjustable by the connected height by the inner and outer prop. The mechanical and mathematical model are developed based on contact mechanics and a serial of full-scale tests were conducted to verify the theoretical model. The test results are well corresponded to the calculated stable load capacity and four batch of props with stable load capacity from 200 kN to 1400 kN were designed. The load capacity of the prop can be adjusted with a small change made to its geometry. The on-site experiment results show that supporting method with this new prop can enhance the stability of surrounding rock and can resist dynamic pressures generated by excavation compared with the wooden cribs. In addition, relative to original supporting costs, new prop can reduce overall supporting costs by 63.8%.