Research On The Evolution Mechanism Of Consolidation-Creep Behaviors Of Saturated Soft Clay Based On True Triaxial Tests

The deformation of saturated soft clay is a considerable factor affecting the long-term stability of the foundation of projects,such as highway and railway,constructed in soft soil area,which is the result of the joint action of consolidation and creep deformation.The strength of the saturated soft clay changes dynamically with the dissipation of pore pressure and the creep of soil skeleton in the process of soil consolidation.It is of great theoretical significance and engineering application value to study the consolidation creep evolution mechanism of saturated soft clay to ensure the long-term stability of soft clay foundations.Yingkou soft clay is taken as the research object and several research methods,such as true triaxial test,microscopic mechanism analysis,theoretical analysis and numerical simulation,are adopted in this paper to study the consolidation-creep evolution mechanism.In the aspect of tests,the true triaxial shear test and drainage consolidation-creep coupling true triaxial test under different confining pressures and different medium principal stress coefficients are carried out.The variation laws of deviator stress,shear strain and body strain in the true triaxial principal stress space are obtained and the strength criterion of soft clay in the principal stress space and the p-q meridian plane is established.In the aspect of micro mechanism,NMR and SEM were used to observe the microscopic evolution process of soil pore and skeleton under the consolidation-creep coupling.In the aspect of theoretical analysis,the change law of structural parameters is studied and the consolidation-creep deformation law and its coupling mechanism of saturated soft clay are analyzed based on the comprehensive structural potential theory.At the same time,a new acceleration element model is introduced,and the nonlinear flow element and constitutive relation of the consolidation-creep of saturated soft clay are proposed.The consolidation-creep coupling model of saturated soft clay considering the effect of principal stress is established,and the reliability of the model is verified based on the experimental data.In the aspect of numerical simulation,the finite element calculation method of the consolidation-creep coupling model is derived based on the finite element formula of the Biot consolidation equation,according to which the numerical simulation program is compiled.Then the evolution laws of stress field,displacement,pore water pressure and plastic strain of an actual soft clay highway foundation are analyzed.The main research results are as follows:(1)The variation rules of partial stress,shear strain and volume strain of undisturbed soft clay and remolded soil are obtained based on the true triaxial test,and the linear relationship between the strength of soft clay and consolidation confining pressure,as well as the medium principal stress coefficient is established,which shows that the consolidation confining pressure and medium principal stress coefficient are positively related to the strength of soil.The strength criterion of saturated soft clay under true triaxial condition is established,and the mathematical relationship between the stress ratio structural parameters and medium principal stress coefficient,as well as the consolidation confining pressure,is obtained.(2)The change of the creep deformation with the stress of saturated soft clay is linear under the low-stress condition and gradually becomes nonlinear when the stress condition increases.The strain rate of saturated soft clay increases with time,and the creep strain increases with the increase of the medium principal stress coefficient.(3)The evolution process of pore fluid medium in the consolidation-creep process is observed based on NMR technology and the evolution process of soil microstructure is observed by the SEM test.The influence of true triaxial condition on soil structure is revealed on the microscopic level.(4)A new accelerated element model is introduced to establish the consolidation creep coupled constitutive model based on the Xi Yuan element model,which is highly correlated with the experimental data.(5)The settlement rate of soft clay foundation increases first and then decreases gradually,reaching the maximum at and near the center point,and decreasing gradually with the distance from the center point.The horizontal displacement of the foundation increases in steps with time.The consolidation-creep coupling model proposed in this paper can better describe the deformation law of soft clay under true triaxial condition.This paper has 80 figures,19 tables,170 references.