Mechanism and application of double active control with pressure-relieving and anchoring for gob-side entry retaining

In terms of the problem of control for gob-side entry retaining under hard roof, the methods of theoretical analysis, numerical simulation and industrial test were used to study the double active controlling mechanism with pressure-relieving and anchoring.Long-term hanging deformation and sudden breaking are the disturbing sources of gob-side entry retaining, while through the technology of active cracking, the changes of broken position, time and structure could reach an active control effect for “large structure” of roof.Transferring the broken position from coal side to the gob side could weaken the interdependent function of rotating block to entry, accelerate the roof breaking to shorten disturbing period, and reduce roof cantilever length to decrease additional loading.Apparent division characterizes the surrounding rock of gob-side entry retaining.Basic load-bearing ring in shallow rock and reinforced load-bearing ring in deep rock constructed with short and long anchor bolts respectively could realize an active control effect for “small structure” of entry.A method of double active control with pressure-relieving and anchoring was proposed to construct fine stress environment, as well as to improve anchoring efficiency and to reduce support density.According to an engineering practice of gob-side entry retaining under 10 m thick hard limestone roof in No.154307 working face of Fenghuangshan mine, a good application result was obtained with anchor bolt support whose row and line distances were designed as 1.5 m×1.5 m after pressure-relieving.