Strengthening effect of cyclic load on siltstone and its macro-micro fracture mechanism

The purpose of this research is to study the strengthening effect of cyclic load on the weakly cemented rock and reveal its microscopic mechanism. In this study, a series of cyclic-to-monotonic loading tests with different cycle numbers were conducted on siltstone. Results show that the strengthening and weakening effects of siltstone under cyclic loading depend on the upper limit of cyclic load. The microfracture mode that was changed by cyclic load is the essential reason for the strengthening effect, according to the study of acoustic emission b-value, sources, and microscopic fracture morphology. Under the cyclic load test, the skeleton area of siltstone can bear the axial load increased. However, the burst of acoustic emission signals is delayed, and the crack scale is small due to the strengthening effect. The difficulty of geotechnical engineering disaster prediction and prevention has increased significantly, and attention should be paid to similar geotechnical engineering. The strengthening and weakening effects under cyclic loading were compared. The strengthening effect on mechanical properties of siltstone was analyzed. The micro fracture mechanism of strengthening effect was revealed.