Laboratory study and constitutive modeling of time-dependent properties of a naturally filled discontinuity

Abstract

Time-dependent properties of naturally filled discontinuities play a critical role in ensuring the long-term stability of tunnels. This study developed a novel sampling method to prepare samples of naturally filled discontinuities, which were then subjected to shear creep tests under varying normal stresses. The time-dependent properties, including creep deformation, instantaneous deformation, steady-state creep rate, and long-term strength, were carefully analyzed. The results showed an exponential increase in cumulative creep deformation and steady-state creep rate with the augmentation of shear stress. Notably, under lower normal stress (0.2 MPa), the local compaction and rotation of stone particles within the fillers of the discontinuity samples lead to a reduction in creep deformation. Drawing on the experimental results, a new rheological element based on the Kachanov–Rabotnov creep damage theory was proposed. By incorporating this nonlinear element in series with the classical Burgers model, a constitutive creep model was established to describe the three creep stages of naturally filled discontinuities. The presented experimental data, and the developed creep model, can serve as valuable references for ensuring the long-term stability and safety of tunnels traversing through discontinuities.