Experimental Study On The Preparation And Mechanical Properties Of Soft And Hard Interbedding Transparent Rock-Like Masses

There are many engineering problems caused by soft and hard interbedding rock masses.Due to the difficulty of on-site sampling,physical model testing is more conducive to observation and research.In order to explore the internal failure mechanism of rock mass,common rock-like materials cannot meet the requirements,and often only the final morphology of the sample after failure can be observed.Transparent rock-like materials possess light transmission performance and economy,and are suitable for testing internal observation of rock masses.However,the physical and mechanical properties of currently developed synthetic transparent rock materials differ greatly from those of natural rocks.Therefore,based on existing research,epoxy resin(ER),curing agent(PEA),and saturated rosin alcohol solution(RSS)are used as bonding agents,and common glass sand(CG)and fused quartz sand(FQ)with similar refractive index are used as aggregates.Based on rock simulation technology and using self-designed molds and device foundations as carriers,a preparation method of soft and hard interbedding transparent rock mass was developed.Three kinds of layer thickness ratios(hard layer thickness:soft layer thickness=1:3,1:1,3:1)and six kinds of layer inclination angles(0°,15°,30°,45°,60°,75°)of soft and hard interbedding transparent rock specimens were successfully prepared.Finally,the influence law of layer thickness ratio and layer inclination angle factors on the mechanical properties of transparent rock mass was analyzed by uniaxial and triaxial compression mechanical tests.In addition,combined with digital images PIV and Matlab,the failure process and internal damage of the soft and hard interbedding transparent rock mass were studied.The main research contents and results are as follows:(1)After 30 transparent rock proportioning tests,two material proportionings suitable for simulating soft and hard rocks were finally found.The ratio of transparent soft rock material ER/PEA/RSS/CG is 27.3/22.7/1.0/179.2,and the ratio of transparent hard rock material ER/PEA/RSS/CG is 33.3/16.7/2.0/154.0.Comparative analysis of the model materials with natural mudstone and sandstone shows that it basically meets the similarity requirements,with a similarity ratio of 1.37.(2)Through uniaxial compression tests on soft and hard interbedding transparent rock samples,the effects of two factors,layer thickness ratio and layer inclination angle,on the stress-strain curve,uniaxial compressive strength,elastic modulus,and deformation modulus are analyzed:(1)Regarding the uniaxial stress-strain curve of the interbedding specimens,the residual stress plateau in the post peak section gradually decreases with the increase of the layer thickness ratio.Under the influence of layer inclination angle,at θ=0°～30°,the post peak section exhibits a plasticity platform,with no significant stress drop,and a generally gentle downward trend;At θ=45°～75°,the post peak section exhibits a residual stress plateau,with a significant stress drop and a generally vertical steep drop trend.(2)Regarding the uniaxial compressive strength of the interbedding specimens,with the increase of the layer thickness ratio,the peak strength of the soft and hard interbedding transparent rock mass gradually increases.With the increase of the layer inclination angle,the change rule of the uniaxial peak strength is not obvious.(3)Regarding the uniaxial mechanical parameters of the interbedding specimens,it is found that the changes in elastic modulus and deformation modulus are linearly and positively correlated with the layer thickness ratio factor,but not linearly with the layer inclination factor.With the increase of the the layer of inclination angle,the elastic modulus generally presents an "M" type trend.The minimum value is obtained at θ=45°and the maximum value is obtained at θ=60°.On the contrary,with the increase of the inclination angle of the layer,the overall change trend of the deformation modulus presents a "W" type.The minimum value is obtained at θ=15° and 45°,the maximum value is obtained at θ=30° and 60°.(3)Through uniaxial compression tests,under the influence of layer thickness ratio and layer inclination angle factors,the fracture evolution mode of soft and hard interbedding transparent rock mass was studied,and combined with digital image acquisition,the failure process of the sample was analyzed:(1)With the increase of the layer thickness ratio,the main fracture of interlayer vertical tension expands and extends,while the development of secondary fractures decreases,and the overall transition from plasticity failure to brittle failure occurs.Under the influence of layer inclination,the failure modes of interbedding specimens can be divided into three types.At θ=0°～30°,the main fracture is axial splitting failure,and the main fracture is vertical tension fracture.At θ=45°,the main fracture is interlayer shear slip failure,and the main fracture develops as interlayer shear fracture,accompanied by secondary fracture development.At θ=60° and 75°,the main fracture is interfacial shear slip failure,and the main fracture develops as shear fracture along the bedding plane,accompanied by horizontal tensile secondary fracture development.(2)Based on digital image acquisition,it is found that the damage area of the sample corresponds to the crack evolution mode.At θ=0°～30°,the vertical tensile crack gradually expands from the hard layer to the soft layer,causing splitting failure,and the corresponding damage area is between the vertical cracks.At θ=45°～75°,shear cracks(inter layer and bedding plane)dominate,and shear failure occurs.The corresponding damage area is between shear cracks.(4)Through triaxial compression tests on soft and hard interbedding transparent rock samples,under a certain confining pressure,the compressive strength of the transparent rock mass increases with the increase of the layer thickness ratio.Under the influence of layer inclination angle,at θ=0°～60°,the compressive strength of transparent rock mass generally shows a downward trend,at θ=60°～75°,the compressive strength begins to rise.The overall change trend is in a "U" shape,and compared to uniaxial compressive strength,the change trend of triaxial compressive strength is significantly more consistent with the Jeager criterion.With the increase of the layer of the inclination angle,the change trend of the internal friction angle and the cohesion force is opposite,and the two show a spiral interactive change rule.