echanical analysis on the stability of surrounding rock structure of gob-side entry retaining

Analyzing thoroughly the characteristics of surrounding rock structure,calculating accurately roadside sup- porting resistance,and controlling serious deformation and failure of rocks surrounding,lead to supporting difficulty in gob-side entry retaining increased,even fail. Therefore,based upon the breaking off characteristics of overlying rock, the mechanical models of big and small structure were built,the formation conditions of low arch and high arch were analyzed,the formulas of their arch rise were derived,and the effect of horizontal force at arch foot on form evolvement and the stability of big and small structure. Research suggested that before the residual boundary of roadside roof the second broke off,if the coal side of roadway was strengthened timely and roadway-inside and roadside supporting re- sistance were improved,then overlying rock was easy to form low arch;if the coal side of roadway was soft,or the sup- porting resistance of roadway was insufficient,then overlying rock was easy to form high arch. Horizontal force at arch foot was the main reason of arch instability,if horizontal force at arch foot was larger than shearing resistance at arch foot,then the arch would lose stability,consequently the arch rise of low arch or the arch span of high arch would in- crease,which caused the overburden load of small structure increase. Overburden load of small structure was not only related to arch form,arch rise and arch span of big structure,but also closely related to the stability of articulated rock of roadway roof in secondary breaking off zone. Based on this,combining with the key strata theory,the locations of hard rock layers and their controlling soft rock group within the scope of arch rise were determined,using slide insta- bility criterion and extrusion deformation instability criterion,the stability of articulated rock of roadway roof was iden- tified from above to below,the overburden load of small structure was determined,and accordingly the reasonable for- mula of roadside supporting resistance were derived.