Experimental Study On Monotonic Shear Behavior And Numerical Verification Of Constitutive Model Of Dense Sands

The construction of ocean engineering is one of the hot spots with the development of society at present. The stress state in seabed soil is complex in the construction process of marine structures. The stress state in seabed soil including magnitude and direction of principle stress will be changed by wave loading and wind loading. Therefore, the effect of variation of the magnitude and direction of principal stress on stability of the foundation should be considered in practical engineering.To study the effects of orientation of the principal stress on the shear behavior of saturated dense sand, a series of monotonic shear tests controlled by the stress were conducted under different initial consolidation stress and different principal stress direction on the soil static and dynamic universal triaxial and torsional shear apparatus in Dalian University of Technology.The test results showed that the principal stress orientation had a significant influence on the effective stress paths and stress-strain relationship of saturated dense sand. Pore water pressure at phase transition point of sand showed an increasing tendency with the increasing of principal stress direction, while the generalized shear stress and peak of the effective deviatoric stress ratio decreased. The stress-strain relationship of saturated dense sand showed strain-hardening phenomenon during the whole shearing process. The tendency of strain-hardening becomed weaker with the increasing of principal stress direction, however, situation of strain-softening of loose sand didn’t occur on dense sand. Generalized shear stress and pore water pressure at phase transition point of sand increased with the increasing of initial consolidated stress. In the condition of the same principal stress direction and different initial consolidated stress, the final steady state of effective stress path of the sand tended to be the same straight line, and the slope of the straight line decreased with the increasing of principal stress direction.A constitutive model which could reflect the effects of variation of orientation of principal stress on the monotonic shear behavior of saturated dense sand was developed on the basis of the improvement of modified Cambridge model and the association between peak of stress ratio and the principal stress orientation through the stress ratio-strain curve obtained from the test. Then user’s subroutine of the improved constitutive equation was established through secondary development of ABAQUS. A model of one element was developed on the basis of ABAQUS software, and the model was also used with the same loading paths as the experiment of this paper to study the effects of the principal stress direction on the monotonic shear behavior of saturated dense sand.By comparing the results of experiment and numerical simulation, it could be concluded that the improved constitutive model may reflect partial effects of orientation of the principal stress on the monotonic shear behavior of saturated dense sand. The tendency of strain-hardening and the generalized shear stress in failure plane became weaker and smaller with the increasing of principal stress direction. The shear-contraction property of sand at prophase stage is amplified, while the shear-dilatancy after the phase transition is not reflected. The improved constitutive model could reflect the effect of the principal stress orientation on the effective deviatoric stress ratio-generalized shear strain better. The results of numerical simulation are basically consistent with the test results.