Damage Properties and Rheological Model of Spatial-Rotation Fissured Red Sandstone Subjected to Freeze-Thaw and Loading

The occurrence of preset flaws can influence the mechanical, physical, and other related properties of rock samples. To study the failure characteristics and crack growth of rock samples containing spatial-rotation (SR) fissures subjected to freeze-thaw (FT) cycles and loading, laboratory tests of SR fissured red sandstone under various factors were conducted. The frost heave pressure, creep deformation, P-wave velocity and damage variable of SR fissured rocks were monitored and analysed. Failure processes and 3D fracture patterns of the specimen were studied in great detail using Digital Image Correlation (DIC) and Acoustic Emission (AE) technologies. Based on the experimental results, a damage constitutive model of the SR fissured rocks under the freeze-thaw and loading (FT-L) was explored. The results revealed that the frost heave pressure can be classified into five types: hibernation, growth, eruption-stabilization, fluctuation, and dissipation. In addition, with the increase of initial damage and temperature (absolute value), the corresponding wave and creep curves increase gradually. Under the coupling of FT cycle and load at each stage, the damage variable exhibited a U-shaped change trend, and gradually increases with the increase of load level. It is worth noting that, the fracture pattern of rock bridge can be classified into three fundamental types (progressive, undulating and opening fracture). A new nonlinear damage constitutive model containing the Nishihara model and a rheological element was established in which the coupling model can characterize the whole creep process of SR fissured red sandstone under the combined action of FT cycles and creep loading. Thus, the proposed model is a very good tool for the analysis of load coupling problems involved in the slope of cold area. The compression tests of spatial-rotation fissured sandstone under the freeze-thaw and loading were carried out.The progressive damage process of sandstone with a spatial-rotation fissure was given.The 3D fracture patterns containing rock bridge extension and fissure penetration were revealed.A damage rheological model that considers the temperature and load was established.