Testing studies of transition zone material of sandstone for Shuangjiangkou high embankment dam are performed with large-scale triaxial apparatus. Through test of constant ?3 stress path on transition zone materials with different sample sizes and different maximum sizes of grain

the influences of D

dmax on stress-strain-strength characteristics are analyzed to study the scale effect that exists in laboratory tests. The results indicate that the failure principal stress

internal friction angle and initial tangent elastic modulus increase as the sample size decreases for a kind of sample with same grading. And the increasing trend of failure principal stress and internal friction angle is obvious under low confining pressure

while the increasing range decreases with the raising of confining pressure. For the same size sample

the failure principal stress and internal friction angle increase with the increasing of maximum sizes of grain and the increasing trend is also significant under low confining pressure.