Mechanics analysis on floor deformation of gob-side entry retaining and prevention and control of floor heave

Dynamic loads which caused by overlying strata caving pass to the floor of gob-side entry retaining through roadside coal,entry-in support and roadside support,consequently cause serious floor heave deformation in a section behind the working face. In order to control the floor heave deformation of gob-side entry retaining which caused by o- verlying strata caving,on the base of analyzing the mechanics environment of gob-side entry retaining,the mechanical model of the floor was established,and the width of elastic compression zone,plastic zone,the fractured zone inside the coal rib and the forces of the coal rib to floor strata were calculated. With the application of key strata theory,the loca- tion and caving order of hard rock strata,and the location of caving limit layer were determined;also,the stripe seg- mentation method of roof load was adopted to calculate the force of roadside support to the floor,and the concept of e- quivalent load was introduced,the mechanical model of floor equivalent load distribution of gob-side entry retaining was established,the overlying strata caving was closely linked with the floor heave deformation of gob-side entry retaining,the influence of overlying strata caving on the stress and deformation of roadway floor was analyzed,and the floor deformation formula of gob-side entry retaining was deduced. The results show that the floor heave of gob-side entry re- taining was caused mainly by the high stress pressure shear failure of floor strata below plastic zone coal and roadside support and the tensile failure of roadway floor and gob floor in strong unloading conditions. Based on this,the preven- tion and control measures of floor heave were put forward,such as reducing the forces of plastic zone coal and roadside support to the floor,improving the force of caved gangue to the floor,preventing the floor strata of roadway from tensile failure,matching the width and stiffness of roadside support with the strength of floor strata. The research results were applied to the engineering practice to provide some references for the prevention and control of the floor heave of gob- side entry retaining.