Abstract：Double-yield surface models for soils are firstly reviewed；and the necessity and reasonability of the concept of double-yield surface are confirmed. Based on a series of tests carried out by an improved plane strain test apparatus on Toyoura and Seto sands，a new double-yield surface model is proposed. The functions for elastic property，plastic volumetric property and plastic shear property in this model are derived directly from the test results with less hypothesis. Young¢s modulus and Poission¢s ratio are derived separately as functions of mean principal stress sm. The spherical surface is adopted as volumetric yield loci and the plastic work is used as hardening parameter. For shear yield loci，a function of principal stresses is adopted，which is derived from the test results and similar to that of Matsuoka model，but the hardening parameter is revised to couple with the unique relationship between hardening surface and the parameter. To simulate the hardening-softening process of the yield loci，the hardening function is built by combining a hyperbolic function and an exponential function. Nonassociated flow rule is adopted for plastic shear property based on test results. To make it convenient to be applied to numerical analysis，the elastoplastic rigid matrix of the model is derived. Finally，by using the parameters derived from the test results，verification of the model is carried out by both interpreting laboratory test results and applying it to calculation of the deformation of a high soil-fill project，Both cases agree well with each other，indicating a potential application of this model.
