Abstract: Basing on the Gens-Alonso model describing the constitutive behavior of unsaturated soils presented in reference [1], the softening mechanism of contaminant concentration on preconsolidation pressure presented in reference[2] and the softening mechanism of contaminant concentration on the cohesion, a constitutive model to describe the chemo-hydro-mechanical coupling behavior of unsaturated soil is developed. The governing equation of the coupling problem consisting with the equilibrium equations combined with the chemo-hydro-mechanical constitutive relations, the governing equations for flow of fluids and contaminant transport, are solved numerically using finite elements. The numerical analyses are carried out to simulate the chemo- hydro-mechanical coupling progress of unsaturated soil around tunnel. Three cases mechanical response, chemo-mechanical elastic response, chemo-mechanical elastoplastic response etc. are compared. The increases in the stress state and the strains in the region close to the tunnel and the shrinkage of the tunnel surface are observed due to the presence of chemistry. The numerical results show the feasibility of the present method to simulate the composite coupling behavior of unsaturated soil.

Key words: plasticity, chemical softening, unsaturated soil, constitutive model