Influence Mechanism Of Interlayer Bond Strength On Prefabricated Rock Beam Instability Research

Layered rock mass is a discontinuous structure composed of rock blocks and bedding planes,joints,fissures,etc.,and widely exists in sedimentary rock strata.Underground engineering built in layered rock mass is constantly emerging,especially the direct roof and old roof of rectangular roadway along the channel.Deformation and instability failure of the top plate such as deflection.In this paper,relying on the 15070 and 15090 roof layered surrounding rock support project of Gongyi Yaoling Coal Industry 15 mining area,taking the prefabricated fractured layered rock beam as the research object,through the indoor three-point bending test and numerical simulation,the layered rock beam is studied.Crack development,detour process and crack propagation mechanism such as induced crack propagation,interlayer bond failure,rock deflection,crack penetration,etc.are induced during bending.The main research work and results are as follows:(1)Ordinary Portland cement mortar is used to prepare sedimentary rock materials,and after multiple sets of adaptations,the mixing ratio of Portland cement(C): quartz sand(S): water(W)is 1:1:0.6.Mortar specimens,physical,mechanical parameters and uniaxial,triaxial compression force-displacement curves are similar to natural sedimentary rocks,and can be used as rock-like materials.Using the layered pouring method,the rock beam specimens with different bond strengths between layers can be obtained by controlling the pouring time interval of the upper,middle and lower layers.The vertical cracks in the middle layer of the specimen and the induced cracks in the lower layer can be prefabricated by inserting plastic sheets into the mold when pouring the specimen.(2)A three-point bending test was carried out to analyze the propagation law of cracks in layered fractured rock beams under the conditions of different bond strengths between layers and different fracture distances.It was found that the expansion of cracks in layered rock beams was due to deflection,penetration or coupling of both.(3)The ABAQUS numerical simulation was used to compare with the results of the physical model test to further explore the crack propagation mechanism of the layered rock beam with prefabricated fissures.Factors such as distance and bearing distance will affect the propagation law of cracks in layered rock beams.