Roadway soft coal control technology by means of grouting bolts with high pressure shotcreting in synergy in more than 1 000 m deep coal mines

Coal mine roadways in more than 1 000 m deep with soft coal suffer severe squeezing and large deformation.Based on the geotechnical and engineering conditions of a maingate of a longwall panel with 7 m high mining height in the Kouzidong coal mine of Huainan Xinji mining area,a case study was performed to investigate the deformation and failure characteristics of the roadway and the failure form of the ground support.Field tests and numerical simulations were carried out to reveal the large deformation mechanism of the maingate in more than 1000 m deep with soft coal,from the aspects of attenuation of anchoring force of bolts and cables,coal deterioration under weathering,strong rheology,etc.The concept of soft coal side control with high pressure grouting bolting and shotcreting in synergy was proposed for the maingate in more than 1 000 m deep.Numerical analysis was conducted to evaluate three types of support patterns including bolts and cables,grouting bolts and cables,and grouting bolting shotcreting on roadway side deformation,and the evolution of fracture and stress fields.The coal side control principle by means of grouting bolting with high pretension and pressure and shotcreting in synergy was expounded.A combined grouting bolt with high strength and pressure,and a grouting cable with high pressure sealer were developed,the mechanical performances and reinforcement effects of grouting bolts,cables and grouting materials were studied,and the soft coal control technology by means of high pretension bolts and cablesmodification with high pressure splitting grouting shotcreting on surface in synergy was formed.The technology mentioned above has been applied in the Kouzidong coal mine of Huainan Xinji mining area,the design pattern and parameters of grouting bolting shotcreting for the experimental maingate were put forward,and underground monitoring was carried out.Field monitoring data showed that this coal control technology significantly improved the structure,integrity and strength of the coal sides.The anchoring force of the rock bolts and cables increased remarkably,giving full play to the active supporting role of the high strength rock bolts and cables.The side to side convergence was reduced by 86% comparing with the initial support pattern.Premature failure of rock bolts and cables was greatly reduced.The proposed soft coal control technology provides an effective alternative for the deep roadways with large deformation.