Variation of Poisson’s ratio of hard rocks during compression and an innovative determination method based on axial loading–unloading test

The Poisson’s ratio of hard rock exhibits a marked stress dependence, which is contrary to its mechanical definition as an elastic constant. Thus, it is of great importance to determine the Poisson’s ratio through a reasonable method. To investigate the Poisson effect of multiple types of hard rocks (sandstone, basalt, granite, and marble), the uniaxial loading–unloading tests are carried out. The test results indicate that whether the tangent Poisson’s ratio or the average Poisson’s ratio, all gradually increases with the stress level. And the stress dependence of the average Poisson’s ratio under the unloading path is reduced, which is significant in the low and medium stress intervals. Appropriately increasing the number of loading–unloading cycles can also improve the stability of the average Poisson’s ratio to some extent. Based on this, a new method for testing the average Poisson’s ratio is proposed, which can effectively exclude the effect of irreversible displacement of rocks and improve the stability of the average Poisson’s ratio. The test procedure is simple and has good application prospects.