The reference[1] suggested the failure stress condition on the maximum cyclic shear surface for saturated sands in 1980s.According to his study

sand will fail when by the criterion that the pore water pressure is equal to the confining pressure.Based on Zhang Ke-xu′s formula and the dynamic triaxial test data of flyash

the failure stress condition on the maximum cyclic shear surface is established in this paper for flyash by using the method of regression analysis to fit curves and derive correlation parameters.In addition

the regression effect of the parameters is tested by the method of F test and the results indicated that the regression effect of the parameters is highly significant.The failure stress condition set up in this paper has shown that the relationship between the initial shear stress ratio and the reciprocal of cyclic shear ratio is not linear but quadratic.This result does not agree with Zhang Ke-xu′s formula which shows that the relationship between the two facts mentioned above is linear.So it can be concluded that Zhang（Ke-xu′s） failure stress condition on the maximum cyclic shear surface is not suitable for flyash.However

further work nust be done to make sure whether the formula set up in the paper is applide to other types of soils.