关键词: 应力应变, 柔度矩阵, 弹塑性, 主对角占优

Abstract: It is demanded that the flexibility matrix have positive main diagonal elements and be diagonal dominant in stress strain relationships of soil．Through the study of the principal stress-expressed flexibility matrix，it is proved that the determinant of the flexibility matrix would be positive if the flexibility matrix satisfies the both conditions．Therefore it could be a method to estimate a constitutive model of soil whether the determinant of the flexibility matrix is positive or not．Finally，the plastic flexibility matrix of traditional elastoplastic models is studied．It is found that the determ inant of the plastic flexibility matrix based on traditional elastoplastic theory is equal to zero，SO the plastic flexibility matrix based on traditional elastoplastic theory could not be diagonal dominant．Consequently a traditional elastoplastic model has its limitation in the description of the mechanical properties of soils．

Key words: stress stain, flexibility matrix, elastoplastie, diagonal dominant