Mechanical behavior of Benxi Formation limestone under triaxial compression: a new post-peak constitutive model and experimental validation

In order to understand the mechanical behavior of limestone and to formulate a new post-peak constitutive model, triaxial tests on the intact Benxi Formation limestone from Gequan mine, Hebei Province, China, were conducted using the Electro-hydraulic Servo-controlled Rock Mechanics Testing System (MTS815). Test results showed that the deformation behavior of the limestone specimens at the post-peak stage was that the axial stress dropped rapidly and the axial strain remained constant for some time before it continued to grow, but lateral strain kept increasing. To explain the deformation behavior and failure mechanism of the intact specimens, mineral composition and microstructure were analyzed using both a polarizing optical microscope and scanning electron microscopy. A tension-shear failure strength criterion was established based on the observed failure modes of the intact specimens. Furthermore, a new post-peak constitutive model was proposed according to the deformation behavior of the intact specimens at the post-peak stage. The proposed post-peak constitutive model was further developed by considering both failure strength criterion and confining pressure. In order to validate the proposed model, experimental data and theoretical results predicted by the proposed model were compared. Comparison of results showed that the new model can capture the post-peak deformation behavior of the limestone well. Additionally, repeated loading tests under triaxial compression were performed to investigate the influence of loading times on the mechanical behavior of the fractured limestone specimens. Test results showed that both the maximum load and plastic deformation of the fractured specimens decreased with increasing loading times.