Bearing and weakening mechanism of triaxial beam structure in roadway laminated roof

In order to solve the problem about attenuation of bearing capacity of roof structure which affects safety and stability of roadway,theoretical derivation,digital experiments and analog simulation method were undertaken to establish a physical and mechanical model of triaxial beam structure of roadway laminated roof.Based on the strength criterion of the Drucker-Prager type,an elastic-plastic analysis method of the triaxial board and bend structure of roadway laminated roof was proposed.The roadway roof of the No.17246 working face in Zhangji Coal Mine in Huainan was analyzed as the object.Based on bearing mechanism and limit equilibrium theory of triaxial beam structure,the ultimate bearing capacity of triaxial beam structure and its influence rule at the post-peak strain-softening stage and residual carrying stage under the special engineering geological condition was deduced with numerical computation software such as Matlab.The results showed that the roadway laminated roof had a long plate structure with lamellar distribution,interaction and partial weight bearing.Based on the characteristic that stress transfers layer by layer through a rock formation,the applied stresses on any rocks in the rock formation could be figured out.The value f was used to determine if shear and compression failure in the triaxial beam structure of roadway roof occur:while f < 0,it was at a shear and compression failure state; while f = 0,it was at the critical state of shear and compression failure; while f > 0,it was at an elastic bearing state and coal roadway roof still had a certain carrying capacity at the post-peak residual stage.The calculation results were obtained that the ultimate load bearing capacity of the roadway roof was about 5.1 MPa and the residual load bearing stress was about 2.9 MPa.Once the excavation of coal roadway begins,roof would undergo elastic bearing,elastic-plastic bearing and plastic bearing.When roof was at the post-peak residual bearing stage and roof structure was perturbated by external stress,a large deformation disaster would probably occur.As confining pressure increases,there are a rising tendency in the rock peak compression strength and the residual compressive strength.The study results revealed the essence of loading capacity weakening of roof structure.