Experimental Study On Effect Of Rotation Of Principal Stress Orientation On Saturated Sand

Mechanical behavior of soil is closely associated with the loading patterns. Test results have shown that larger plastic volumetric strain as well as higher growth rate of pore water pressure would be generated in multi-directional shearing than in a single-directional one. Lower resistance of sand to liquefaction was also observed under the rotation of principal stress orientation. Principal stress rotation is the typical stress path when seismic or wave load is applied on the soil. But the study in this aspect is less, and almost all the existing research data is about circular path. It has been hardly studied for more general condition of oval path. Moreover, initial stress condition has significant influence on the dynamic behavior of sand. As a basic and important issue in the evaluation of the stability of seabed and ocean engineering structures, the complex initial anisotropic stress state as well as the complex variation pattern of cyclic stress must be taken into consideration in studying the deformation and strength properties of sands. For this sake, plenty of shear tests under oval paths were designed and performed on Fujian Standard Sand using the soil static and dynamic universal triaxial and torsional shear apparatus. The present research is supported by the National Natural Science Foundation Key Project of Study on Engineering Properties of Marine Soil and Deformation Mechanism of the Foundation (No. 50639010) and the National Natural Science Foundation Project of Study on Constitutive Model of Soil under the Complex Stress Condition and its Application in Seabed Dynamics (No. 50179006). Experimental study on rotation of principal stress orientation was focused on. The main content of the current research are as follows:1. Plenty of bidirectional shear tests under oval paths were designed and performed to research the deformation and strength characteristics of saturated sand. The research can remedy the deficiency of previous study on circular path only. The results show that, when compared to the results of circular paths tests, the dynamic intensity of sand gained in oval paths tests changes in a wide range, and the deformation properties are more complicated.2. The effect of magnitude ratio of normal stress difference and shear stress on dynamic resistance of saturated sand has been researched by special designed contrast tests. The results show that, when the bounding area of oval paths is kept constant, a critical value of the stress magnitude ratio could be found, under which the highest resistance of specimen is observed. The more the stress ratio deviates from the critical value, the lower intensity of sand is behaved. Initial orientation of the major principal stress, consolidated deviator stress ratio, and initial coefficient of intermediate principal stress all have effects on the critical value. The corresponding critical value range is given in chapter 3.3. Dynamic strength characteristics of saturated sand under complex initial stress condition have been researched. The results show that, the dynamic strength of sand is strongly depended on initial orientation of the major principal stress and consolidated deviator stress ratio, but less associated with initial coefficient of intermediate principal stress. The reference variation range of resistance of sand changing with the influence factors is given.4. Dynamic strain response of saturated sand under complex initial stress condition has been researched. Factors influence the development of dynamic strain are analyzed such as initial orientation of the major principal stress, consolidated deviator stress ratio, initial coefficient of intermediate principal stress and amplitude of cyclic stresses. A unified development model of dynamic strain for different consolidated deviator stress ratio has been put forward.5. The development characteristic of dynamic pore water pressure is investigated by analyzing the time-history curve of pore water pressure and considering various influence factors. The results show that, consolidated deviator stress ratio has the most significant effect on normalized pore water pressure developed with number of cycles. And the normalized pore water pressure developed with generalized shear strain is independent of various initial stress condition. Then the development model of residual pore water pressure with cyclic numbers and generalized shear strain are both established.