Study On Double-sided Bounding Surface Model Of Cement-treated Clay Under Cyclic Loading

Cement-treated clay is a kind of artificial structural soil that mainly relies on hydration reaction,pozzolanic reaction and carbonation reaction in the cement and a series of complex physical and chemical reactions between cement and clay mineralogy to improve the soft clay.With the wide application of cement-treated clay in road,railway,port,reclamation and other projects as well as the pollution of sludge solidification governance,this thesis starts from the constitutive model theory,according to the triaxial shear test results to study the stress-strain relationship of cement-treated clay under complex loading.Three important bounding surface parameters are estimated using curve fitting to data obtained from the undrained triaxial tests on cement-treated clay in the p-q space and the stress update implicit algorithm of the proposed bounding surface model is established.Then,the genetic algorithm is applied to realize the minimization of the objective function in the parameter fitting process.At last,the stress update explicit algorithm of the double-sided bounding surface model under cyclic loading is established.The work of this thesis is as follows:1.In the double-sided bounding surface model,the concept of modified mean effective stress is introduced to characterize the structure of cement-treated clay,which is the sum of the mean effective stress and cementation.The expression of the cementation shows that the degradation is related to the plastic shear strain,which can reflect the cumulative loss process of the structure of the cement-treated clay with the plastic shear strain.In order to realize the stress renewal calculation under cyclic loading,the stress update implicit algorithm is established for the double-sided bounding surface model.2.In order to fit the parameters of the proposed bounding surface model of the cement-treated clay,the genetic algorithm is introduced into the optimization calculation of the objective function to minimize the objective function.The corresponding program is developed to realize the nonlinear test data fitting.The numerical simulation results of undrained triaxial test of cement-treated clay show that the proposed constitutive model can describe the brittle failure and strain softening under high confining stress of cement-treated clay,as well as the stress path bends to the left to prediction failure envelope of cement-treated clay,which is above the critical state line of the untreated clay.With the losing of cementation,the stress path will eventually return to the critical state line.3.The stress update explicit algorithm of the double-sided bounding model of cement-treated clay under cyclic loading is studied.Considering the great influence of stress mapping factors to mapping process in the process of reloading and unloading,the explicit sub step calculation scheme and Pegasus search algorithm are applied to establish the stress updating display algorithm of the cement-treated clay double-sided bounding surface model.The characteristics of the undrained triaxial shear test of the cement-treated clay under cyclic loading are calculated and analyzed by the program compiled.