Study On Constitutive Model And Expansion Law Of Sandstone Structure

In the construction of large-scale geotechnical engineering projects,rock mass presents different mechanical behavior under different geological conditions,and with the development of infrastructure construction,complex geological conditions need to be often faced,and traditional and single rock theories are difficult to summarize.In order to describe the structural characteristics of rock mass and simulate the law of cracking damage of rock mass under loading,comprehensively consider the theory of elastoplastic mechanics and damage mechanics,and at the same time correct the effective stress principle caused by hydrostatic pressure and the shear resistance of the material itself,a modified constitutive model considering the damage effect is established based on the original Drucker-Prager yield criterion,and the secondary development is realized in the application of finite element software ABAQUS,and the full enumeration method is used to determine the model parameters.Validate model validity and apply it engineering.The results show that the written program can carry out the simulation study smoothly,and the determined model parameters can better describe the stress-strain relationship of sandstone materials.The main research contents of this thesis are:(1)The modified Drucker-Prager yield criterion considering the influence of hydrostatic pressure was established,the object-oriented programming method was adopted,the elastoplastic damage constitutive solution program was compiled,the Fortran program language was used to debug the UMAT subprogram interface on the ABAQUS software platform to achieve secondary development,based on the test data of sandstone materials,the image direct determination method and equation solution method were used to determine some parameters.The constitutive model parameter inversion program was prepared to determine the established model parameters in the remaining modified constitutive model,and the comparison test curve was in good agreement with the improved model calculation curve,indicating that the constitutive correction and parameter determination had certain validity.(2)Based on the improved constitutive model,a numerical model of sandstone components running through different prefabricated fractures was established,and only the fracture cracking under uniaxial compression was simulated,and it was concluded that the45°fracture inclination angle and double parallel fracture type had the greatest damage degree to the material.According to the similar theory,the fracture sandstone components at different angles were prepared,and the fracture growth law of sandstone was studied through uniaxial compression and true triaxial compression tests,and it was concluded that the peak strength of the material increased with the increase of the fracture inclination,and the maximum value was obtained when the fracture inclination angle was 75°,and the new fracture growth of fracture-like sandstone structures was mostly airfoil cracks,and the component failure mode was mostly compression shear failure.Under different medium principal stress states,with the increase of medium principal stress,the overall trend of stress-strain curve of the material tends to be consistent,the yield stage is more obvious,the peak strength increases,and the degree of material failure is strengthened.(3)Based on the modified Drucker-Prager yield criterion and the determined model parameters,the tunnel engineering excavation example related to this type of sandstone material is simulated on ABAQUS software,and the results show that after soil excavation,the settlement of the tunnel is small,in a safe state,and meets the excavation requirements;Furthermore,an XFEM extended finite element method fracture rock damage evolution analysis model based on BP neural network was established,and the comparison between the training results and experimental data showed that the prediction effect of the model was satisfactory,and the strain and stress prediction of this type of material could be completed.