Effect of structural anisotropy on compressive creep behavior of composite rock based on digital image correlation

Abstract In this study, a series of uniaxial creep tests were conducted on three-dimensional printed (3DP) composite rock specimens to investigate the effects of structural anisotropy on the time-dependent behavior of the rock. Digital image correlation (DIC) was used to monitor the evolution of the full-field strain during creep tests. The Burgers model was used to analyze the anisotropic creep behavior of the composite rock. When the specimen was subjected to a low creep stress (σcr ≤ 0.55σc (failure stress of the specimen)), the creep strain was mainly induced by transient creep, and the transient creep parameter Ek exhibited increasing order-shaped anisotropy. When the specimen was subjected to a high creep stress (σcr ≥ 0.70 σc), the creep strain of the specimen was dependent on steady creep, and the steady creep parameter ηm showed U-shaped anisotropy similar to the compression strength anisotropy of the specimen. DIC observations showed that the strain concentration along the soft layer was an important factor that resulted in anisotropic creep, and the time-dependent shearing slip between the soft layer and hard material enhanced the creep anisotropy under a high creep stress. The failure modes of the specimens showed that creep failure developed first in the soft layer, and the creep process had an insignificant influence on the failure modes of the composite rock.