Decomposition of stress increment and the general stress-strain relation Of soils

In the light of matrix theory, the character of stress increment which cause the rotation of principal stress axes is analysed and the general stress increment is decomposed into two part: coaxial part and rotational part. Based on these, the complex three dimensions(3-D) problem involving the rotation of principal stress axes is simplified to the combination of the 3-D coaxial model and the theory about pure rotation of principal stress axes that is only around one principal stress axe. The computative method in detail of general 3-D problem is provided and other applications ate presented also.