## 1 Introduction
[4] performed uniaxial compression tests to understand the mechanical behavior of holed sandstone using the DIC method. Compared to the intact specimens, those artificially holed ones show almost half of the expected mechanical performance depending on hole shapes. DIC technology is able to visualize strain and displacement fields to consistently profile failure patterns. The digital image correlation method was used by [PERSON] and [PERSON] [20] to successfully assess the mode I fracture parameters including process-zone magnitude and critical opening displacement for Berea sandstone with a three-point bending test. The tensile fracture features covering opening displacement and crack size were identified, showing that over all the tests, process-zone retains a stable length and critical opening. [PERSON] et al. [21] examined the micro behavior of mode I crack of sandstone due to varied loading speeds using acoustic emission and digital image correlation. All the previous studies are helpful in facilitating the understanding and characterization of mechanical behavior and performance of sandstone components within various application contexts. Nevertheless, in the existing literature several disadvantages are associated with DIC applications. First, based on a literature search, few studies have been carried out yet to particularly concentrate on the dynamic failure process to obtain full-field strain values of sandstone which can provide more direct, specific, and deeper information on a sandstone failure course. Moreover, to the best of our knowledge, no studies have been performed to systematically examine the specific thresholds of failure strain of sandstone materials. Finally, most studies used the DIC technique for sandstone behavior investigation without knowing the reliability and accuracy of the obtained results. The present research expects to fill out this research gap. Compared to the existing literature, this study provides a more specialized and detailed investigation into the full-field strain of sandstone under different loading scenarios by examining multiple representative field regions using DIC. Different from previous studies, this research especially explores the specific failure thresholds of sandstone materials. Advantageous over the literature, this study combines three different methods including optical DIC, theoretical analysis, and finite element simulation for the cross-check of result accuracy. By conducting uniaxial compression experiments on sandstone, this paper proposes to use the state-of-the-art digital image correlation method to gain the full-field strain of sandstone model subject to the process of uniaxial compression. In particular, deep investigations are carried out on four typical points selected from the four areas and moments of the full-field failure. These four points are considered to be the typical representatives characterizing the specimen failures course. A total of 12 specimens with identical dimensions are tested. Dynamic strain-time curves are derived, corresponding to the four chosen points in the course of the compression test in order to detect the range values of failure thresholds for sandstone samples. Based on the obtained thresholds, failure patterns can then be forecasted for sandstone, and further, the pertinent structure components and systems. The DIC processing results are cross-checked by the Hill-Tsai failure criterion and finite element method (FEM), which have been widely used for analyzing failure mechanisms from two distinct perspectives.