Study On Mechanical Properties And Failure Characteristics Of Rock Mass With Weak Sandwich

Different from the general single-lithological rock mass,this rock mass has obvious anisotropy,composed of dominant rock mass and inferior rock mass superimposed interactionally,the interlayer combination is tight,and there are often various macroscopic fractures and other defects inside the inferior rock mass.The mechanical properties and deformation characteristics of composite rock mass are not only affected by the mechanical characteristics and failure characteristics of the interlayer structural surface and the constituent rock mass,but also by the internal fractures,inferior rock mass thickness and inclination angle of the rock mass.Composite rock mass with soft interlayer is a kind of composite rock mass,and the existence of soft interlayer hides great safety hazards to engineering construction,so it is necessary to study its mechanical properties and failure characteristics.The study was carried out by combining indoor experiments and numerical simulations.The main research contents and conclusions of the paper are as follows:(1)Using 42.5 ordinary Portland cement,river sand and water,three similar materials,two soft and hard rock materials with large differences in mechanical properties were determined by ratio test,and a single type of rock standard sample was made for uniaxial loading test and Brazilian splitting test to obtain the basic mechanical parameters of the two types of rock materials.(2)Composite rock mass specimens with different interlayer thicknesses and inclination angles were made for uniaxial loading test,and the acoustic emission data during the specimen test were recorded,the strength deformation characteristics,acoustic emission characteristics and failure mode of uniaxial compression were analyzed,and the mechanical properties and failure characteristics of the specimen were summarized by the influence of the interlayer thickness and inclination angle.(3)Based on the physical test to obtain the basic rock mechanical parameters,the PFC2 D program was used to establish a numerical model of the rock mass containing soft sandwich,and the uniaxial loading test of the rock mass containing soft sandwich was numerically simulated and analyzed,the mechanical properties and failure mode of the sample were compared with the indoor test,and the change law of the number of microcracks in the process of the sample test with the thickness and inclination angle of the interlayer was analyzed.(4)Based on the PFC2 D program,on the basis of the above tests and numerical simulations,a composite rock mass sample with precast fracture was established,and the macroscopic mechanical characteristics,micro-crack propagation evolution process and failure characteristics of precast fracture composite rock mass with different inclination fractures,different interlayer thickness composite rock mass with precast fracture,and different interlayer inclination composite rock mass with precast fracture were analyzed,and the influence of the existence of precast fractures on composite rock mass samples was discussed.