Macro And Micro Damage Characteristics Of Shanghai Soft Clay Under Different Stress Paths

With the rapid development of urbanization process in China,the engineering construction of large and medium-sized cities in soft soil area is becoming much more.There are many engineering disasters happened because of the lack of awareness of mechanical properties about soft soil under the different stress paths during the construction and designment.So,it is important to study on the mechanical properties and damage of the soft soil.The anisotropic consolidated and undrained triaxial tests of Shanghai soft clay under four kinds of stress paths are carried out by using the GDS triaxial apparatus,and the micro scanning tests of Shanghai soft clay are carried out under the different paths by Field Emission Scanning Electron Microscope.The strength and deformation behaviors as well as the macro and micro damage characteristics are studied,the stress paths' infuences on macro and micro parameters are analyzed,and the damage development under the different stress paths are investigated.The research shows that the stress-strain curves of Shanghai soft clay mainly are manifested by the hardening and softening characteristics under the different consolidation pressures and the different stress paths.The stress at failure point increases with the increasement of the consolidation pressure.The strength under the unloading path is less than that of the loading path.The pore pressure evolution is related to the loading and unloading paths.The pore pressure under the unloading conditions is less than that under the loading conditions.The stress path has the strong effects on the strength of soil.The strength parameters of the triaxial tension are lower than that of the triaxial compression.The micro parameters of soft clay are influenced by the different stress paths,different stress levels,different scanning positions and the different magnifications.The flatness of particles and pores increase with the increasement of the stress ratio at first,and decrease when the stress ratio reaches the peak point.The flatnesses of two ends of specimens are larger than that of the medial layers.The form factor of particles and pores decreases with the increasement of the stress ratio.And the two parameters under the unloading stress path are lower than that under the loading stress path.The void ratio and the fractal dimensions of two ends of specimens are lower than that of the medial layers.The void ratio and the fractal dimension increase with the increasement of the stress ratio.The two parameters under the unloading stress path are larger than that under the loading stress path.The void ratio and the fractal dimension of particles are exponential to the stress ratio,while the pore fractal dimension of has the liner regression relationship with the stress ratio.The macro and micro damage variables are presented,which are linear to the stress ratio.Soft clay damage variable under loading path is less than that under unloading path.The results in macroscopic and microscopic views on damage evolution are the same for soft clay.