Abstract:

A series of undrained cyclic triaxial tests were conducted on calcareous sand from the South China Sea, Fujian silica sand, and Nanjing fine sand. The liquefaction flow characteristics and evolution mechanism of soil state of saturated sand under different influencing factors were studied based on the proposed tension and compression apparent viscosity η_ct  . The main conclusions are summarized as follows: (1) Considering that the hysteresis loop of shear stress-strain rate of saturated sand during cyclic loading is asymmetric during the extension and compression stages, a definition of η_ct / η_o that accounts for the disparity in fluidity during these two stages is proposed to assess the liquefaction flow characteristics of sand. (2) The relationship between normalized apparent viscosity ratio (η_ct / η_o , where η_o is the η_ct -value of the first cycle) and the excess pore ratio (r_u) is found to be independent of relative density (D_r), loading frequency (f), cyclic stress ratio (CSR) and consolidation confining pressure ( σ'_c). It is initially identified that the unique development mode between η_ct / η_o and double-amplitude shear strain (γ_DA) remains unaffected by variations in sand type, the initial soil state, and loading conditions. (3) Both flowability difference parameter λ and the tension and compression apparent viscosity gradient Δη_ct / η_ct  initially increase and subsequently decrease as r_u increases, and the r_u corresponding to the peak value of these two are essentially identical, and can be regarded as the initial liquefaction point of soil. A method is proposed for distinguishing the physical states of sandy soil during liquefaction into solid, solid-liquid, and fluid stages.

Key words: tension and compression apparent viscosity, liquefaction flow characteristic, soil state, pore pressure ratio, double amplitude shear strain