Study On The Best Aspect Ratio Of Standard Test Specimens For Rock Material During Deformation And Failure

Rock materials vary in dimension or size,and their physical and mechanical properties often typically exhibit significant differences.Studies have shown that the rock material has obvious size effect,and the diversification of aspect ratio has a significant influence on its deformation and failure process,fracture morphology,compressive strength,stress-strain response and energy response.The obtained rock strength and deformation characteristics,through indoor experiments on specific size rock samples,can not be directly applied in the actual geotechnical engineering design.Therefore,it is necessary to study the optimal aspect ratio of rock material deformation and failure process.Based on the constitutive relation of rock,which considering the initial damage evolution characteristics of rock materials,the optimal aspect ratio of rock samples during rock material deformation and failure is studied.The optimal aspect ratio of rock is derived from the theoretical point of view.The theoretical model about the size effect of compressive strength and energy dissipation per unit volume is proposed,which considering the initial damage evolution characteristics of rock materials.Through a series of uniaxial compression tests of granite samples with different aspect ratios,the rupture morphology,compressive strength and energy dissipation of rock material failure are studied and analyzed with the change of aspect ratio.At the same time,through the comparative analysis of experimental results and theoretical expressions,the accuracy of the obtained theoretical model is demonstrated,and the optimal aspect ratio of rock materials is discussed.The uniaxial compression simulation test of rock was carried out by the finite difference program FLAC3 D.The six groups of granite samples with aspect ratios of 1,2,2.5,3,3.5 and 4 were numerically tested.The relationship between the rupture morphology,the stress-strain response and the aspect ratio was analyzed,in the uniaxial compression deformation process of rock materials.And the numerical simulation results,the experimental research and theoretical research results were compared each other.On this basis,the influence of the aspect ratio on the energy evolution in the process of rock deformation and failure is studied.Based on the above research,it is considered that the best aspect ratio of rock material during deformation and fracture is 2.5.