Surrounding Rock Control Mechanism And Application Of “Support-Unloading” Combined Technology For Gob-Side Entry Retaining In Shallow Coal Seam

This article took the Hejiata Coal Mine in Shaanxi Province as engineering background,means of theoretical analysis,similar simulation in the lab,numerical simulation,field measurement were used to study the surrounding rock control mechanism and application of“support-unloading”combined technology for gob-side entry retaining in shallow coal seam.The roof activity rule and surrounding rock deformation characteristics of the roadway were simulated.The mechanical model of the roof structure was established and the formula of the roadside support resistance at different periods of roof movement was calculated.Moreover,the pressure relief mechanism of hydraulic fracturing was clarified.The coordination relationship of the stiffness of the roadside support system and the synergistic relationship between the roadway support and the roadside support were proposed.The "support-unloading" combined technology for gob-side entry retaining was proposed and the underground test was carried out.The main results are as follows:(1)The laboratory three-dimensional similar simulation test,UDEC and FLAC3 D numerical simulation software were used to simulate the overlying rock activity law of shallow coal seams and the characteristics of roof activity in different periods were obtained The plastic zone of the solid coal side of the roadway was 2.2m,and the basic roof cantilever length was 15 m.(2)A mechanical model of the roof for the gob-side entry retaining was established.The roadside resistant in the stage of immediate roof movement was calculated,and the formulas of the roadside support resistance under the given deformation and limited deformation in the stage of main roof movement were obtained.(3)The mechanism of hydraulic fracturing pressure relief was clarified,and the influence of hydraulic fracturing on the immediate roof and main roof morphology were analyzed.The influence of hydraulic fracturing on the cutting force of concrete pillar,on the roadside support resistance under given and limited deformation conditions were calculated.(4)The formulas for the stiffness of the roadside support system composed of "roof-concrete pillars-floor" and the deformation of concrete pillars were deduced,and the factors affecting the stiffness of the system and the deformation of concrete pillars were analyzed.The coordinated relationship between the roof,concrete pillars and floor was obtained.(5)The supporting effect of the bolt(cable)on the surrounding rock were analyzed.The influence of the roadway support on the value of the resistance of the roadside support was calculated,the coordinated relationship between roadway support and roadside support was analyzed.(6)The "support-unloading" combined technology for gob-side entry retaining was proposed,including hydraulic fracturing technology,high-strength bolt and cable support in the roadway,roadside concrete pillar support and reinforced support of shield in the roadway;(7)The underground test of the "support-unloading" combined technology for gob-side entry retaining was conducted in the Hejiata Coal Mine.The maximum subsidence of the roof was 40 mm,there was almost no bottom heave,and the roadway retention effect was good.