This paper describes the formulation of a three�dimensional elastoplastic analysis for a pile�soil system and its application to an actual in�situ test. In the formulation, the subloading surface model is adopted for the elastoplastic constitutive relation. This model falls within the framework of unconventional plasticity, in which the plastic strain rate due to the stress rate inside the yield surface is taken into consideration. Thus it is capable of describing smooth transition from elastic

more »

... to plastic state, which is necessary to describe the softening behavior of a soil. In addition, the Mohr�Coulomb model is also adopted, in order to compare with a conventional model in which the interior of the yield surface is assumed to be elastic domain. These constitutive relations have been implemented in a three�dimensional elastoplastic analyses, based on which analyses of lateral loading test of a single pile�soil system were conducted. The results show a fairly good agreement between the analysis and the test for overall deformation behavior of the pile and the soil.