With the large-scale triaxial apparatus

triaxial tests of gravel soil for a 300m high embankment dam were carried out; the highest confining pressure is to 5 MPa. The experimental results show that the stress-strain curve of gravel soil is a hyperbolic one; and that shear strength envelope of gravel soil is nonlinear. According to physical meaning of Duncan-Chang model

initial modulus Ei should be obtained in the area of minimum value of axial strain εa; and ultimate principal stress difference (σ1－σ3 )ult from a bigger range of εa; so propose that Ei is obtained in the area of εa=0%-3% and (σ1－σ3 )ult in the area of εa=5%-15%. The proposed method is more reasonable than the traditional method because the actual strain of high earth dam is about 1%

. As the confining pressure of the triaxial test is in a large range

confining pressure is divided into three parts

such as 0.2-1.0 MPa

1.5-3 .0 MPa

3.5-5.0 MPa; and the tangent modulus in each range of confining pressures are gained respectively. It is proved to be reliable by the comparison between test data and computing data.