Creep properties and constitutive model of diabase in deep water conveyance tunnels

Abstract

Aiming at the creep characteristics of the surrounding rock of the Haidong water conveyance tunnel of the Central Yunnan water diversion project and taking the diabase at the tunnel fault zone as the research object, compression creep tests were conducted under a range of confining pressures, revealing the axial and lateral creep characteristics of diabase. Based on the theory of fractional derivative, a nonconstant coefficient Abel dashpot considering damage was established, and the simplified equation form was used to facilitate parameter identification and calculation. By combining a nonlinear Kelvin model, a classical element model, and a simplified Abel dashpot that accounts for damage effects, a constitutive model was established to describe the diabase creep process. The constitutive relations for one-dimensional and three-dimensional creep were provided. The results show that the sample exhibits both a decay creep stage and a steady-state creep stage when the stress level is below the diabase's stress threshold; when the stress level surpasses the threshold, the sample goes through an accelerated creep stage with a quickly growing creep rate and ultimately fails. Diabase mostly experiences axial creep deformation at low-stress conditions, followed by more significant lateral creep deformation under high-stress conditions. Comparing the triaxial compression creep test curve with the theoretical curve revealed that the model more accurately characterized the nonlinear creep properties of diabase.