Abstract:Based on the stress-strain relation of Q3 loess triaxial compression tests with different stress paths,including conventional axial loading,lateral unloading,and constant mean principle stress with different water contents of 2.0%,8.5%,15.0%,and 18.0%,the initial tangent modulus were obtained. It was shown that the initial tangent modulus of structural loess decreases with increasing lateral consolidation pressure but decreases with increasing water content,and the damage of loess structure subjected to compression stress is more serious than its hardening due to compressing. Because the initial tangent modulus decreases gradually with the increase of compression stress and water content and reflects the structural damage increase of loess,this parameter can be used to define the damage variables by the composite theory. A structural damage ratio of Q3 loess was proposed by the change of initial tangent modulus between the initial tangent modulus of undamaged loess and completely damaged loess. With the consideration of the coupled action of compression and water content,the constitutive model is proposed in terms of the damage ratio,which is a new approach for evaluating the possible collapse settlement of loess foundations.