Theoretical and Numerical Investigation of Rock Flexural Strength Determined by the Four-Point Bending Test

It is of great significance to study the flexural properties and behaviour of rock in rock mechanics and engineering applications, such as tunneling, mining and underground space development. However, there are few studies related to the flexural properties of rock considering different elastic parameters in tension and in compression. This study focuses on rock flexural strength subjected to bending loading. A series of four-point bending tests (FPBTs) on prismatic beams of granite were carried out. The flexural strength of rock was theoretically determined under different assumptions based on the elastic and elastic‒plastic theory considering different elastic properties of rock in tension and in compression. Then, a comparison was made between the indirect tensile strength measured by the Brazilian test and the flexural strength acquired from the FPBT. The effects of specimen shape and heterogeneity on the flexural behaviour of rock were analysed by FEM-based numerical simulation. The results show that the calculated flexural strengths considering the elastoplastic and bimodulus properties of rock are lower than those without considering the properties and are closer to the Brazilian tensile strength of rock. The flexural strengths of rock increase with increasing ratios of height to thickness. Heterogeneity plays a crucial role in the flexural properties of rock. The more homogeneous the rock is, the higher its flexural strength. The findings in this paper facilitate a better understanding of the flexural properties of rock.