Numerical Simulation Of Deformation-cracking Processes Of Double-layer Beams And Mining Height Effects Of The Stope

Using the continuum-discontinuum method in which the Lagrangian element method,deformational discrete element method and fictitious crack model are coupled,deformation-cracking processes of double-layer beams under three-point bending and processes of the deformation,bed separation and collapse of double-layer beams under uniform load-excavation are modeled,and effects of the mining height on variations of abutment pressures and deformation,bed separation and collapse of horizontal strata are modeled.Firstly,size effects and effects of mechanical parameters on deformation-cracking processes of double-layer upper-hard-lower-soft beams and upper-soft-lower-hard beams under three-point bending are studied.It is found that:(1)load-displacement curves of two kinds of double-layer beams exhibit five typical stages:the elastic stage prior to the first peak,the softening stage beyond it,the hardening stage prior to the second peak,the brittle failure stage beyond it,and the residual stage;(2)when the upper beam only cracks or when the upper beam rapidly cracks during cracking of the lower beam,a single peak and an instability can be observed;when the lower beam has completely cracked and then the upper beam cracks or when cracks propagate alternately in the upper and lower beams,double peaks or several peaks can be observed;(3)the first peak load of the load-displacement curve depends on the interaction of the upper and lower beams;the second peak load depends mainly on the action of the upper beam.Secondly,effects of the single beam height on processes of deformation,bed separation and collapse of double-layer beams under uniform load-excavation are modeled.It is found that.for upper-hard-lower-soft with an decrease of the height of the lower beam,the height of bed separation increases;for upper-soft-lower-hard,bed separation appears.Finally,effects of the mining height on variations of abutment pressures and deformation,bed separation and collapse of horizontal strata are studied.It is found that with an increase of the mining height,the peak of the abutment pressure decreases and the distance from the peak of the abutment pressure to the working face increases;the first bed separation of the immediate roof is earlier,and the development height of bed separation is increased before the height of bed separation develops to the bottom of the medium sandstone.