Multisurface Chemoplasticity. I: Material Model for Shotcrete

Employing a thermodynamic framework, chemomechanical couplings for shotcrete are treated in this paper. A new material model based on multisurface chemoplasticity is presented. It accounts for hydration kinetics and chemomechanical couplings related to the strength growth and the evolution of stiffness properties as well as for autogeneous shrinkage in early-age shotcrete. The underlying intrinsic material functions, which are independent of field and boundary conditions, are determined from standard material tests. As for the numerical treatment of the constitutive equations of the material model, an extended form of the return mapping algorithm is proposed. The constitutive equations are applied to a two-surface chemoplastic model, consisting of a Drucker-Prager loading surface and a tension cut-off. In a companion paper, the proposed material model is employed for 2D structural analyses of tunnels driven according to the New Austrian Tunneling Method.