Clay, as the most common soil used for foundation fill, is widely used in various infrastructure projects. The physical and mechanical properties of clay are influenced by the pore solution environment. This study uses a GDS static/dynamic triaxial apparatus and nuclear magnetic resonance experiments to investigate the effects of cyclic loading on clay foundations. Moreover, the development of cumulative strain in clay is analyzed, and a fitting model for cumulative plastic strain is introduced by considering factors such as NaCl solution concentration, consolidation stress ratio, and cycle number. In particular, the effects of the NaCl solution concentration and consolidation stress ratio on the pore distribution of the test samples before and after cyclic loading are examined, and the relationship between microscopic pore size and macroscopic cumulative strain is obtained accordingly. Our results show that as the consolidation stress ratio grows, an increasing number of large pores in the soil samples are transformed into small pores. As the NaCl solution concentration becomes higher, the number of small pores gradually decreases, while the number of large pores remains unchanged. Cyclic loading causes the disappearance of the large pores in the samples, and the average pore size before cyclic loading is positively correlated with the axial cumulative strain after cyclic loading. The cumulative strain produced by the soil under cyclic loading is inversely proportional to the NaCl solution concentration and consolidation stress ratio.
