Impact of structural anisotropy on compressive creep behaviors of composite rocks based on digital image correlation technology

Anisotropic creep behaviors of the composite rocks significantly affect the long-term stability of the deep tunnels in those rocks. To investigate the influences of structural anisotropy on creep behaviors of composite rocks, a series of uniaxial creep tests were conducted on composite rock-like specimens with different dip angles. The rock-like specimens were manufactured by three-dimensional printed (3DP) method to avoid high variability of natural rocks. The Burgers model was used to fit the creep curves of the composite rock, and the fitting results showed that the transient creep parameter E_k (elastic module of the Kelvin element) exhibited an increasing order-shaped anisotropy with increasing dip angle under low creep stress levels, while, the steady-state creep parameter η_m (viscosity coefficient of the Maxwell element) showed a U-shaped anisotropy under high creep stress level. The digital image correlation (DIC) technology was used to capture the distribution and evolution of the full-field creep strain of the composite rock, and the observations showed that the anisotropic creep behaviors of composite rock were related to the strain concentration along the soft layers, and enhanced by the time-dependent shear slip between the soft layers and the hard material under high creep stress.