Control mechanism of roof fracture in no-pillar roadways automatically formed by roof cutting and pressure releasing

Abstract

The technology of automatically forming a no-pillar gob-side entry retaining by roof cutting and pressure releasing (RCPR) effectively cuts off the stress transfer in roofs by directional pre-splitting. Meanwhile, the rock mass of the gob roof falls and fills the gob, taking advantage of the work done by the mining pressure and the broken expand characteristics of the rock mass. Thus, roadways in mining areas are automatically formed, reducing the roadway excavation amount, eliminating reserved coal pillars, and preserving coal resources. The core of this technology is the formation of a roof-cut short-arm beam structure in the roof of the automatically formed roadway (AFR). The fracture location and morphology provide the fundamental basis for the design of the roof cutting and support parameters of the AFR. In this study, the dynamic evolution pattern of the surrounding rock of the roof in the no-pillar AFR by RCPR is analysed to clarify the roof fracture and control mechanisms. The Hoek-Brown failure criterion and the upper bound method are used to establish the fracture mechanics model and the fracture curve equation of the roof in the AFR by RCPR, and the influences of the fracture range of the roof-cut short-arm beam are analysed. The results show that with an increase in the strength of the surrounding rock, the pre-tightening force of the anchor cable, the gob-side roof support force, and the support force of the broken expand gangue or a decrease in the stress of the surrounding rock, the mining influence coefficient, and the cutting angle, the fracture range of the roof-cut short-arm beam gradually transfers towards the solid coal side and the stability of the AFR is enhanced. The findings from this study can provide a theoretical basis for the design of control schemes, including the cutting and support parameters of the no-pillar AFR by RCPR.