Multisurface chemoplasticity. I: Material model for shotcrete

Employing a thermodynamic framework, chemomechanical couplings for shotcret e are treated in this paper. A new material model based on multisurface che moplasticity is presented. It accounts for hydration kinetics and chemomech anical couplings related to the strength growth and the evolution of stiffn ess properties as well as for autogeneous shrinkage in early-age shotcrete. The underlying intrinsic material functions, which are independent of fiel d and boundary conditions, are determined from standard material tests. As for the numerical treatment of the constitutive equations of the material m odel, an extended form of the return mapping algorithm is proposed. The con stitutive equations are applied to a two-surface chemoplastic model, consis ting of a Drucker-Prager loading surface and a tension cut-off. In a compan ion paper, the proposed material model is employed for 2D structural analys es of tunnels driven according to the New Austrian Tunneling Method.