Liquefaction And Dynamic Stress-strain Research For Saturated Sand Based On Disturbed State Concept

Identification of liquefaction in saturated sands under Dynamic or cyclic loading is vital for analysis and design of structures and foundations.Empirical criteria based on index properties have provided useful methods for such analyses and design. However.it is recognized that fundamental micro-structural considerations are required for enhanced understanding and general procedure for liquefaction analysis. Disturbed state approaches are considered to be the fundamental and mechanistic method,which reflects the material deformation and failure through the micro-structural changes of physical and mechanical processes.In this paper,the research status of liquefaction in saturated sands has been reviewed,and the mechanism,influencing factors and traditional empirical identification methods of liquefaction have been summarized.In order to reflect the disturbance of soil micro-structure,a identification approach for liquefaction based on Disturbed State Concept is proposed though establishing a disturbed state function characterized by internal disturbance of soils.The disturbance of saturated sands subjected to un-drained cyclic triaxial loading is investigated at different cyclic numbers,cyclic stress ratios,initial mean effective stress,relative density.particle characteristics.It is observed that when the cyclic stress ratio is small,the disturbed state function increase slowly with the progressive cyclic numbers,and can reach critical value D_c or not at a higher number of cycles. When the cyclic stress ratio is larger,it can reach the critical value at small cycles. The influence of the initial mean effective stress on the disturbed state function is not significant under the same cyclic stress ratio.The larger the relative density,and particle size of soil,the greater the cyclic numbers for disturbed state function to reach the critical value D_c.and the stronger the liquefaction resistance is.The relation between disturbed state function and cvclic numbers,plastic axial strains as well as pore water pressure is established on the basis of tests.Based on the test results,a modified Hardin-Drnevich model based on Disturbed State Concept is proposed.The model which incorporates the variation rule of dynamic secant shear modulus of unloading and reloading curve as well as the influence of disturbed damage in the cyclic process can reflect the non-anti-symmetric law of the unloading and reloading curve.The dynamic stress-strain relationship describes well the non-anti-symmetry of the unloading and reloading curve,and is highly accurate under small-strain conditions.