Roadway strata control technology by means of bolting-modificationdestressing in synergy in 1 000 m deep coal mines

In order to overcome the difficult problems associated with the roadway large deformation in the coal mines with 1 000 m buried depth,soft rock and intense mining induced affect,the causes of large rock deformation and bol- ting component damage were analyzed on the basis of a maingate in a working face with extra-long width located in the Kouzidong coal mine,the Xinji mining area,China. The rock large deformation mechanism under the superposition ac- tion of high in-situ stresses and intense mining induced stresses around the face with extra-long width was revealed from following aspects:rock property degradation,rock dilatancy caused by deviatoric stresses,structural rheology of soft rock,and mining induced affect,by means of theoretical analyses,laboratory tests and underground experiments. The synergy strata control idea with bolting-modification-destressing was put forward for the roadways with 1 000 m buried depth,soft rock and intense mining induced affect. The rock stresses,deformation and damage features around roadways unsupported,and controlled by rock bolting,bolting-grouting modification,and bolting-grouting modification- hydraulic fracture destressing,were studied through numerical simulation,and the synergy strata control principle is ex- pounded. The CRMG700 rock bolt rebar with extra-high strength and high impact toughness was developed,and the mechanical response features of the bolt under tension,shear,torsion,bending,impact load and various combination were revealed. The micro-nano inorganic and organic grouting composite materials and high pressure split grouting technique were developed. The hydraulic fracture destressing technique and facilities were developed,which form the roadway synergy control technology with bolting-modification-destressing. Based on the above-mentioned achievements, the rock control pattern and parameters were put forward with bolting-modification-destressing for the experimental en- try in the Kouzidong coal mine,and the field experiment and monitoring were conducted. The monitoring data demon- strated that the entry deformation was decreased by more than 50% ,the broken percentage of bolts and cables was re- duced by 90% ,and the mining induced stress was obviously mitigated after the rock synergy control technology was applied,which effectively contained the large deformation of roadway with 1 000 m buried depth,soft rock and intense mining induced affect.