Stress-dependent lateral stress behaviour of rigid sand-soft tyre chip particulate mixtures

This study explores the coefficient of lateral stress at rest (K0) of sand-tyre chip mixtures, addressing a knowledge gap in the behaviour of rigid-soft particulate mixtures. A modified oedometer cell was used to investigate the effects of applied vertical stress and overconsolidation ratio (OCR) on K0. Experiments were conducted on mixtures with varying size ratios (SR = 0.57, 1.43, and 2.50) and tyre chip contents (TC = 0%, 10%, 20%, 40%, 60%, and 100%). Results revealed a non-linear relationship between K0 and TC. For mixtures with OCR ≤ 4, K0 initially increased by ≈50% from TC = 0% to 10%, then decreased by ≈30% up to TC = 40%, and eventually converged to that of pure tyre chips. The inclusion of tyre chips led to stress-dependent K0 responses, particularly at high TC (TC ≥ 40%), and reduced the influence of stress history on K0 due to their high elastic recoverability. To capture the complex K0 behaviour of rigid-soft mixtures, a modified K0-estimating equation incorporating stress-dependency and a new OCR-adjustment parameter was proposed. These findings can contribute to more accurate design guidelines for utilising recycled materials, promoting sustainable construction practices and advancing the understanding of rigid-soft mixtures.