Multifractal analysis and critical slowing down study on the strain field of siltstone under uniaxial compression

Non-destructive testing technology can accurately detect the precursors of rock failure, and it is a crucial means to ensure the safety of major projects. Uniaxial compression was carried out on siltstone, and the non-destructive testing technology of digital image correlation method was used as the monitoring means. By integrating deformation energy density and multifractal theory, the precise capture and fine quantitative characterisation of the strain field on the rock surface were achieved. On this basis, based on the critical slowing theory, the precursive signals of the multifractal parameters of the main strain field were analysed. Results indicate that: The changes in the deformation energy density on the rock surface and the multifractal parameters Δα and Δf(α) of the principal strain field are closely related to the rock fracture process. The variation of multifractal parameters shows a critical deceleration phenomenon, and the variance is more explicit than the precursory information of the autocorrelation coefficient. The influence of window length and lag step size on critical slowing parameters can be ignored. This research framework fills the gap in the use of DIC technology for the early warning of the non-uniformity of rock strain fields.