Cyclic deformation of granular materials in principal stress space- experiments and prediction

The permanent deformation of unbound granular materials (UGMs) is a key factor affecting the long-term performance of flexible pavements. This study investigates the influence of intermediate principal stress on the deformation behaviour of pavement materials under undrained conditions. The findings indicate that the variations of intermediate principal stress amplitude remarkably influence the strain accumulation patterns. Additionally, the results reveal that both resilient strain and modulus vary with changes in the intermediate principal stress. The distance to the failure line was defined as Δ by normalizing the applied stress ratio. Larger Δ consistently coincided with larger terminal slopes, indicating a shift from shakedown to sustained accumulation as the applied stress ratio approached the failure slope. To capture this stress-dependent behaviour, a mechanistic-empirical prediction model was proposed to capture the stress-dependent behaviour of UGMs. This model incorporates the effects of stress history and the intermediate principal stress, making it more adaptable to the realistic pavement loading conditions. • The study examines how intermediate principal stress affects cyclic deformation of granular materials. • Higher b cyc reduces axial strain accumulation. • Resilient strain and resilient modulus change notably with variations in b cyc . • A larger normalized distance to the failure line (Δ) leads to more sustained permanent strain. • The proposed model incorporates intermediate principal stress to accurately predict permanent deformation.