Characterization and Influence Analysis of Constraint Stiffness in Rock Indentation Test
摘要
Rock indentation test is an effective technical method for evaluating the mechanical properties of rocks. However, indentation tests currently face a variety of test conditions. They can be conducted on laboratory samples of different sizes, samples with constraint structures or in-situ rock masses. These various test conditions lead to differences in constraint stiffness, and whether constraint stiffness affects indentation tests has become a critical factor in determining the applicability of indentation results. To access the influence of constraint stiffness on indentation test, a characterization model for constraint stiffness was developed to quantify it under different test conditions. Combining laboratory tests and PFC-FLAC 3D coupled numerical model, the influence of constraint stiffness on the indentation index and fracture characteristics was investigated. The findings reveal that constraint stiffness significantly affects indentation characteristics of rocks with different lithologies. A high constraint stiffness leads to an increase in the obtained mean indentation index (MII), and the increase in MII is more significant for hard rocks with the increase in constraint stiffness ratio. Increased constraint stiffness further suppresses fracture propagation in rock samples during indentation. For indentation tests under different laboratory or in-situ conditions, the results can be harmonized through an indentation index convertion based on constraint stiffness.