Numerical Analysis Of Sandstone Energy Evolution Based On Modified Mohr-coulomb Criterion

The instability and destruction caused by the excavation of large rock mass engineering,both at home and abroad,such as some slope excavation,tunnel excavation instability phenomenon,such as to the safety of construction personnel and caused huge losses and hidden dangers,such as the development and even immeasurable.Although many scholars have proposed a lot of constitutive models for rock materials so far,there are still few rock calculation models considering loops and unloading under high confining pressure,as well as some numerical methods,nowadays can not well simulate and analyze some problems such as rock engineering stability.Therefore,it is necessary for higher confining pressure loop and elastoplastic numerical simulation of the rock mass unloading conditions were studied.In thesis,sandstone is taken as the research object,coulomb yield criterion based on Mohr elastic-plastic constitutive model,and analyzes the evolution of energy within the sandstone,gives the basic properties of sandstone and modified Mohr-coulomb constitutive procedures,analysis of test data,the relationship can explore the plasticity and confining pressure,and the test results and simulation,data analysis and discussion describe sandstone evolution process of the internal energy.Rock elastic-plastic phase occurs before the injury,Mohr-coulomb criterion is commonly used as a theory,in judging whether the rock material yield,the calculation analysis will appear slow convergence,the shortcomings of complicated calculation process and a series of inevitable,all of this reflects the need we to traditional Mohr-coulomb criterion puts forward improvement measures,to take some method to compensate for the insufficiency,a By fitting the inflection point on the yield surface,the fitted hyperbola approximates the yield function.The method of modification involves geotechnical numerical analysis.In order to solve the problem by geotechnical numerical analysis.Firstly,to improve the Mohr-Coulomb is very necessary,the first partial derivative of yield function and the first partial derivative and second partial derivative of potential function are calculated.Finally,it can be applied to the plastic modification of rock elastic-plastic constitutive model.To correct the Mohr-coulomb elastic-plastic constitutive theory as the foundation,through the modified Mohr-coulomb criterion UMAT subroutine written and used in the software,respectively the mechanics of sandstone under different confining pressure and the energy analysis,the write the UMAT subroutine of calculated results with classic Mohr-coulomb criterion of ABAQUS,co MParing the calculated results Verify that the UMAT subroutine is error-free and accurate.The UMAT subroutine was used to analyze triaxial cyclic,The loading tests under different confining pressures and the changes and influences of the calculated results of stress and strain are studied respectively.On this basis,according to the conservation of energy,and energy to write programs,and combined with the test data,are summarized based on the modified Mohr-coulomb criterion of rock elastic-plastic constitutive model algorithm and energy evolution,which provides a new idea for it.The results show that the yield stress calculated by the UMAT subroutine is slightly smaller than that calculated by the Moore-Coulomb constitutive model of ABAQUS.This is because in the correction process,Change the yield surface position of Mohr-Coulomb criterion,conduct internal fitting correction,that is,the fitted curve is inside the original curve,so the stress calculated by the UMAT subroutine is smaller than the actual one.When m=0.3,the model enters the plastic state earlier through the UMAT program than without the program,and the yield stress at this time is not much different from the results calculated by the Mohr-Coulomb constitutive model in ABAQUS.By adjusting the value of M,the compression properties of sandstone can be reflected.In this state,the calculation results of UMAT subroutine are closer to the reality.Through five different confining pressure under triaxial cyclic loading simulation test,it can be found that the change of energy in sandstone has three stages,namely,accumulation of energy,release of energy and dissipation of energy.At the same confining pressure,the compressive property of sandstone is enhanced when elastic deformation occurs.When plastic deformation occurs,the plastic energy inside the sandstone begins to increase,and the elastic energy decreases but the variation is small.Under the condition of different confining pressure,sandstone plasticity can increases with the increase of confining pressure.Co MPared with the results,it is found that with the increase of confining pressure,peak strength is also growing,numerical simulation of maximum peak intensity is smaller than the test process,However,the curve trend is consistent with the test results,verify the correct application of maneuverability.Based on the theory of Mohr-Coulomb yield criterion,the elastic-plastic constitutive model for numerical simulation of sandstone,good results have been achieved.The accuracy and reliability of the algorithm are verified by uniaxial and triaxial cyclic loading tests in laboratory.