Investigation of Permanent Deformation Behaviour of Subbase Layer Mixed with Non-Plastic Stone Dust of the Pavement

The investigation centred on the performance of the well-graded, unbounded subbase layer in the pavement, incorporating varying amounts of stone dust (SD) by weight (1, 2, 3, 5, 7, 10, 15, 20, 25%). It assessed the mix's strength through the California bearing ratio (CBR) test and analysed permanent deformation (PD) behaviour under both multi-stage and single-stage loading conditions using repeated wheel load tests (RWLT) on mixes placed over the subgrade with a 6% CBR value. As SD content increased, the mix's dry density and optimum water content increased, while the void ratio decreased due to SD filling voids in coarse particle–matrix. The addition of SD had a negligible impact on the CBR value. However, PD behaviour decreased by incorporating SD into the control mix. In terms of PD under dry conditions, the mix with 10% added SD (SD-10) demonstrated the least sensitivity to load increases and repetitions during multi-stage loading, exhibiting a low rate of PD. Similarly, under single-stage dry mix loading, SD-10 showed the lowest PD at a design load of 560 kPa compared to other mixes. Specifically, the PD of the subbase under dry conditions for the mix SD-10 decreased from 2.27 to 1.91 cm under multi-stage loading and from 2.23 to 1.54 cm under single-stage loading compared to the control mix (SD-C), highlighting enhanced deformation resistance with the addition of non-plastic SD particles to the subbase layer. Introducing water into the mixes increases the PD behaviour. For the control mix (SD-C), PD increased from 2.18 cm in the dry state to 2.83 and 3.03 cm after single-stage loading at 36,000 cycles with water content at OMC and OMC + 1.5%, respectively. Despite the high fine particle content, the mix SD-10 exhibited the lowest PD, indicating improved performance with the strategic addition of SD to the mix.