Meso/Microscale Parameter Correlation Model of Sandstone Based on the Hoek-Brown Criterion and Parallel Bond Model

Sandstone is an important and common engineering rock, and understanding the meso/macroscale mechanical properties of sandstones under different confinements are crucial for engineering safety. It is still difficult to correlate the mesoscale bonding parameters and macroscale mechanical behavior. In this paper, the Hoek-Brown parallel bond correlation model (HB-PBCM) is proposed based on the mesoscale analysis of the parallel bond model (PBM). The mathematical analytical expression of HB-PBCM is derived from the sensitivity analysis of the PBM parameters to the Hoek-Brown criterion strength parameters. The model is able to reproduce both the PBM and HB parameters obtained from laboratory tests. The parameters were validated via numerical tests, where the final strength and failure patterns of sandstones are shown to be consistent with those via real experiments. Combined with the numerical and experimental results, we find that the macroscale brittle-ductile transition of sandstone is characterized by the alteration of the tensile-to-shear crack ratio, different mesoscale crack distributions, and mesoscale crack accumulation rates.