Coupled effect of unloading rate and water content on mortar under differential cyclic loading

Repeated excavation and fluctuations in water levels subject mortar to varying stress rates and moisture conditions; however, the coupling effects of these factors remain insufficiently studied. This research examines the combined influence of unloading rate and water content on the mechanical behavior of water-bearing mortar (WM) under multi-level differential cyclic loading (MDCL). Experiments were conducted on specimens with three representative water contents (0.00%, 6.99%, and 13.98%) under multiple unloading rates. The results indicate that both factors affect mechanical properties and interact synergistically. Critical thresholds were identified at a water content of 6.99% and an unloading rate of 2.0 kN/s, marking distinct transitions in energy response. A strong linear relationship was observed between cumulative strain increment and the number of MDCL cycles, which may facilitate failure prediction. Both loading and unloading moduli were highly sensitive to moisture content and unloading rate, with MDCL enhancing the overall stiffness of the material. These findings contribute to a deeper understanding of the coupled effects of water content and unloading rates on mortar under MDCL, offering valuable insights for assessing the stability and deformation of WM structures in engineering applications.