# Predictive Modeling and Experimental Analysis of Cyclic Shear Behavior in Sand-Fly Ash Mixtures
## 4 Results and Discussion
This wide loop suggests that clean sand retains high strength with minimal permanent deformation (i.e., 92 kPa and \(-\)76 kPa) (Figure 7a). When fly ash is added, at a content of 2.5% (FA2.5), the loop shows slight narrowing, reflecting a minor decrease in strength and energy dissipation. This change suggests that the inclusion of fly ash initiates mixtures to reduce capacity to resist deformation under cyclic loading (Figure 7b). The hysteresis loop becomes noticeably narrower for FA5, signifying a further reduction in strength and a greater tendency for permanent deformation after each loading cycle. This shift suggests that with 5% fly ash, the mixture's ability to recover from cyclic stress is compromised, making it more vulnerable to cumulative strain (Figure 7c). The FA10 specimen, containing 10% fly ash, continues this trend with an even narrower loop, indicating a marked decrease in energy dissipation and strength (i.e., 89 kPa and \(-\)79 kPa). This mixture shows more pronounced deformation with each cycle, suggesting that a higher fly ash content further reduces the sand's resilience to cyclic loading (Figure 7d). At 15% fly ash (FA15), the hysteresis loop is significantly compressed, showing a decline in strength and energy dissipation capacity. This mixture exhibits high permanent deformation after each cycle, reflecting a loss of resilience and a growing susceptibility to shear-induced damage (Figure 7e). The spherical shape of fly ash particles allows them to roll easily over one another, reducing resistance during shearing within the specimens. Consequently, replacing angular sand particles with fly ash particles decreases the shear strength of sand-fly ash mixtures, emphasizing the significant role of particle angularity in shear strength [42]. In the FA20 specimen with 20% fly ash, the horizontal stress at the end of loading cycles corresponds to 100 kPa and \(-\)79 kPa for the final loading cycle, which demonstrate that the inclusion of additional fly ash causes an increasing effect (Figure 7f). Figure 6: First-quarter cyclic shear behavior of tested specimens. [PERSON] et al. [32] indicate that the changes in the inter-particle void and micro fabric more strongly influenced the cyclic resistance of the fly ash-sand mixtures. For fly ash-sand mixtures, the degree of relative compaction, the confining stress, and the mixture ratio all affect the stress-strain and volumetric behavior of an ash mixture under shearing [41]. The FA content is the only varying parameter explaining this gradual reduction in shear behavior. As fly ash content in the sand-fly ash mixture increases, the hysteresis loops progressively narrow, signaling a loss of strength, energy dissipation, and resilience under cyclic loading. The transitional fine content is used as an indicator to determine whether the specimens behave as sand-dominated or fine-dominated [46; 47; 48; 49]. Moreover, 15% FA into sand as an inclusion ratio was observed to cause transitional limit behavior in this study between sand and fly ash. The further increase in fly ash content in the mixtures imparts denser packing within the matrix [42]. The addition of the 20% fly ash material led to an increase in the cyclic shear strength of the tested sand-fly ash mixtures. Figure 7: _Cont._