Abstract: Dynamic triaxial tests were conducted to clarify the dynamic deformation characteristics of silty clay in flood irrigation areas under cyclic loading, using single-sample stepwise and multiple samples of constant amplitude. The effects of confining pressure, bias consolidation ratio, drainage conditions, dynamic load frequency, and cyclic stress ratio on the development law of cumulative plastic strain and residual dynamic pore pressure, the evolution characteristics of the hysteresis curve, and the change law of softening index of silty clay were studied. The results show that the development of cumulative plastic strain and residual dynamic pore pressure of soil under dynamic load is consistent. According to the stability theory, the dynamic behavior of samples under different test conditions can be divided into three typical cases: plastic stability, plastic creep and incremental failure. Under the basic conditions of this test, the boundary cyclic stress ratios of the three dynamic states of plastic stability, plastic creep, and incremental failure are around 0.30 and 0.40, respectively. The hysteresis characteristics of undrained specimens in the plastic stable state are obvious, and the hysteresis curve shows an S shape. With the progression of loading, soil experiences stiffness degradation. The cumulative plastic deformation of undrained specimens is smaller than that of drained specimens, and the softening index of soil under drained and undrained conditions remains stable at around 1.15 and 0.91, respectively, under lower cyclic stress ratios. Through grey relational analysis, it is found that the cyclic stress ratio has the greatest influence on the cumulative plastic strain and pore pressure ratio. The confining pressure exerts the greatest influence on the softening index. The parameters of the cumulative plastic strain model suitable for silty clay in flood irrigation areas have been determined, and the prediction effect is good.

Key words: dynamic triaxial test, silty clay, cyclic stress ratio, cumulative plastic strain, softening index