Abstract: In the aim of providing reference for the design and construction of expansive soil fill in subgrade, the calculation method for the bulging deformation of expansive soil was analyzed. First of all, one-dimensional linear expansive ratio test on weak expansive soil of different initial dry density under varying overburden pressure was conducted, and the law of moisture equilibrium of expansive soil fill in subgrade was expounded. With reference to the results of one-dimensional linear expansive ratio obtained by other scholars, the concepts of relative overburden pressure and relative deformation were put forward. Test results unveiled that the relative linear expansive deformation was in a power exponential relation with relative overburden pressure. In addition, the wet expansive deformation model was established and a practical calculation method for bulging deformation of expansive soil fill in subgrade was proposed to solve the coupling problem of three factors for the linear expansive ratio of expansive soil.

Key words: expansive soil, subgrade, bulging deformation, relative deformation, linear expansive ratio