| Constitutive models of unsaturated soil become more and more mature,and its ability to describe mechanical behaviors is greatly enhanced,which brings a large number of model parameters.The increase in the number of model parameters is bound to make it more and more difficult to determine values of parameters.Therefore,based on the optimization theory of genetic algorithm,combined with the experimental results and numerical calculation of unsaturated soil constitutive model,this paper realizes the optimization of model parameters,improves the prediction accuracy of the model,and promotes the application of unsaturated soil constitutive model in practical engineering.The main research contents of this paper are as follows:(1)The numerical implementation of the BBM unsaturated soil constitutive model and the optimization of model parameters were carried out.Firstly,cutting plane stress integration algorithm was proposed for BBM unsaturated soil constitutive model.In the elasticity prediction stage,the influence of suction on the volumetric strain was considered.In the plastic correction stage,the number of yield surfaces was determined by judging the positive and negative of yield surface functions.Secondly,the Solve-G function suitable for unsaturated soil constitutive model of double independent stress was proposed.The strain increments required for numerical simulations were obtained through the elastic constitutive relations,and the iterative correction of unbalanced forces was performed.The numerical calculation program of BBM unsaturated soil constitutive model was written in Fortran language.Thirdly,genetic algorithm was selected as the optimization algorithm.For the genetic algorithm,the real number coding method was selected,the simulated binary cross operator and the dynamic random mutation operator were introduced.Combined with the numerical calculation program of the model,the optimal solution of parameters was obtained by minimizing the difference between experimental results and predicted results of the model.Finally,the comparisons between the experimental results and the predicted results of four groups of consolidation,wetting and shear tests were carried out.The results shown that constitutive model combined with parameter optimization well predicted the deformation behavior of unsaturated soil.(2)The numerical implementation of a critical state-dependent constitutive model for unsaturated soils and the optimization of model parameters were carried out.Firstly,cutting plane stress integration algorithm of the critical state-dependent constitutive model for unsaturated soils was proposed.For the liquid phase,the effect of volumetric strain on degree of saturation was considered.For the solid phase,the influence of degree of saturation on the volume strain was considered.Secondly,the Solve-G function suitable for the hydro-mechanical coupled constitutive model of unsaturated soil was proposed.The strain and effective degree of saturation increments were obtained through the elastic constitutive relations.Thirdly,genetic algorithm was selected as the optimization algorithm.Combined with the numerical program of the model,the optimal solution of the parameters was obtained by minimizing the difference between the experimental results and the predicted results of the model.Finally,the comparisons between the experimental results and the predicted results of four groups of wetting and shear tests were carried out.The results shown that the constitutive model combined with parameter optimization well predicted the hydromechanical coupling behavior of unsaturated soil. |
