Abstract: A constitutive model of hardening soil and small-strain-hardening soil was established to simulate the loading–unloading characteristics accurately. Mathematical equations for the constitutive models of the hardening and small-strain-hardening soils were de-rived using the yield function, plastic potential function, and flow law. Dynamic-link data were compiled using the VC++ language, and the loading and invoked interfaces were modelled using FLAC3D 3.0. Test results for classical cases of small-strain model development were compared to verify the rationality of the hardening soil model with small-strain stiff-ness. The constitutive model was used to simulate the deep foundation excavation of the Oasis Center in Shanghai, and the actual measurement results were compared with those of the small-strain-hardening soil, hardening soil, and Mohr–Coulomb ideal elastic–plastic models. The analysed data of the hardening and small-strain-hardening soil models were in good agreement with the measurements. This study provides a reliable constitutive model of deformation control for large-scale geotechnical projects.

Key words: small strain, hardening soil, constitutive model, FLAC3D, foundation exca-vation