Span increasing effect and control technology of coal roadways in deep soft ground

Aiming at the problems of serious damage of surrounding rock and supporting difficulty in the deep soft rock roadway, taking the gob-side roadway of the LW21106 working face in Chengjiao Coal Mine as the engineering background, a mining induced span increasing model was established and the formation mechanism mining-induced span increasing effect was revealed.By developing a transverse and longitudinal curved beam model of the roadway roof, it is concluded that the lateral stress on the roof, equivalent span of the roadway, and coal rock strength are the main controlling factors for the damage of surrounding rock of roadway.Finally, control measures were proposed and field trial was conducted.The research results show that roadway has experienced"initial stability-fractures development-shear slider aggravation-equivalent span increase" with the mining influence.The maximum normal stress of the roadway roof is positively correlated with the stress concentration coefficient, equivalent span of the roof, size of the roadway section and burial depth.Tensile and shear failure occurred in roadway roof in high stress environments.Therefore, increasing the number and pre-tension of the roof anchor cables is beneficial for enhancing the integrity of the roof.Based on the main controlling factors of roadway deformation, a collaborative control strategy of "surrounding rock reinforcement-pressure relief-reinforcement support" is proposed.Based on the on-site conditions, a control technology includes roof cutting along the lateral wall of coal pillars, grouting reinforcement, supplementing anchor cablesfor strengthen support in the fractured area is adopted.The field trial shows that the maximum displacement coal pillar is 18.89 cm, the roof subsidence of is 25.86 cm, and the maximum displacement along the unmined coal wall is 29.65 cm.The effective control of the coal roadway surrounding rock deformation provides a scientific basis for controlling the soft surrounding rock deformation in the deep coal mine.