Sand Response To Multi-way Dynamic Loading

The simulation of seismic effects in indoor test frequently adopts the "simplified procedure for evaluating soil liquefaction potential " advanced by Seed. This simplified procedure only considers the shear stress of seimic effects which is simulated in the 45°face of soil sample by one-way dynamic triaxial test. The result based on it has been widely used in project. However by analyzing the seismic stress, there is some difference in stress between the simulation with one-way dynamic triaxial test and the real seismic condition, and the two-way dynamic triaxial test can factually simulates the seismic stress.On the basis of former studies, the effects of seismic stress history on the small strain shear modulus G_max of Fujian sands and Qiantangjiang silts with different relative density under one-way and two-way dynamic is inverstigated. The test results presented indicate that both G_max will produce additive attenuation under cyclic dynamic loading, and the relative density take no effect on Fujian sands but obvious effect on Qiantangjiang silts. The strain has direct relation with the additive attenuation of G_max. Multi-way dynamic loading will not influence the the additive attenuation of G_max.Secondly, this paper emphasely contrast and analyze the cyclic behavior of Fujian sands under the simulation of seismic loading with one-way and two-way dyniamic triaxial test. The results indicate that under low destroy cyclic number(N_f <30), there are no obvious difference between them in the cyclic behaviour such as pore pressue,strain,cyclic intensity,effect stress load and backbone line. However under the high cyclic number(N_f / >30), their cyclic behaviour shows obvious difference. In the seismic condition(N_f<30), it is reasonable that one-way dynamic triaxial test substitutes the two-way dynamic triaxial test.Finally, to research the reason of the difference between one-way and two-way dynamic loading, undrained cyclic spheric loading triaxial tests were on conducted on saturated Fujian sands. The result shows that when the cyclic number is lower than 3000, the cyclic behavior of sands has no changes; and when it is higher than tens of thousand, the residual pore pressure has an obvious cumulation. On this basis, this paper gives out a deduction that the difference between one-way and two-way is by the reason of the intercross effect of cyclic spheric stress and cyclic deviator stress.