Influences of the Height to Diameter Ratio on the Failure Characteristics of Marble under Unloading Conditions

Failure characteristics of rocks under different loading and unloading conditions have been an important subject of laboratory tests. This study aims to investigate the influence of the height to diameter (H/D) ratio on the failure characteristics of marble specimens under unloading conditions. Conventional triaxial unloading (TU) tests were performed on marble specimens of 50 mm diameter with different H/D ratios from 0.5 to 3.0. Moreover, for comparison, uniaxial compression (UC) tests and conventional triaxial compression (TC) tests were conducted on marble specimens with different H/D ratios. The results indicate that the failure strengths of the specimens, including the UC strength, TC strength, and TU strength decrease with the increase in specimen height, and the decreasing trend can be fitted with a function that is deduced from Weibull's theory. The specimens with lower H/D ratios (0.5 and 1.0) underwent tensile failures in the TU tests, whereas the specimens with higher H/D ratios (2.0 and 3.0) showed shear failures in the TU tests. In addition, the analyses of strain energy evolutions indicate that the unloading failures of the specimens with lower H/D ratios are an ongoing process and the unloading failures of the specimens with higher H/D ratios present a sudden process.