Parameter Inversion Of Micro Constitutive Model For Concrete Materials Based On Macro Experimental Data

The discrete element method is one of the most extensive and effective methods applied in rock and concrete mechanics among the numerical method of discontinuous mechanics.Determining the microparameters through macroscopic mechanical tests is the key problem restricting the further application of the discrete element method.In order to simulate the occlusal effect of concrete aggregate,a random CLUMP particle generation method that does not change the model porosity and does not add or delete particles is proposed.The method is used to establish a uniaxial compression test and a splitting tensile test model for PFD^3D and the simulation is conducted.With reasonable simplification,5 microparameters which can control the macro response of materials are selected for parameter inversion.Four degree polynomial without cross terms is used to construct the response surface which establishes the mapping relationship between microparameters and macro response.An objective function is defined as the minimum of mean square deviation of the calculated and observed values of macro response and the inversion values of microparameters are obtained by solving a unconstrained optimization problem.The results obtained by PFC^3D simulation using the inversion values are compared with the experimental results,and the minimum mean value of the relative error of the macro response at each load step is 5.58%which proves the validity of the microparameters inversion and the rationality of using CLUMP particles.Based on the microparameters obtained from inversion,PFC^3D modeling and simulation of segmental joint of Nanjing Yangtze tunnel are carried out.The simulation and experimental results are consistent on the overall trend.The stress state of the concrete segmental joint is given by measurement sphere in PFC^3D.Result shows that the upper part of the segment is compressed,and the bolt part is pulled,which consistent with common cognition.The feasibility of using PFC^3D to simulate concrete segmental joints is demonstrated.