When a material is subjected to cyclic loading, there are changes in the material's geomechanical behaviour that need to be characterized for a safe design. For unbounded granular materials, the shakedown theory is used to explain the soil's behaviour under cyclic loading. However, it is not clear yet if such theory is extendable to unreinforced and fibre-reinforced stabilized soils. To this end, a series of unconfined compression cycling loading tests were performed, to study the effect of the number of cycles and initial deviatoric stress level on the behaviour of an unreinforced and reinforced stabilized soil. The results were analysed in terms of shakedown theory, elastic and plastic deformation energy and damping ratio. It was observed that shakedown theory seems to represent the behaviour of the stabilized unreinforced and fibre-reinforced soils under cyclic loading, with threshold between the plastic shakedown and the plastic creep shakedown behaviour at around an absolute axial strain 1 x 10-3. The effect of increasing binder content (from 12 to 39%), comparable to reducing the initial deviatoric stress level (from 85 to 15%), promoted a reduction in plastic deformation (from 2.09 to 0.19% without fibres, and 2.21 to 0.24% with fibres) and damping ratio (from 25.17 to 10.01% without fibres, and 29.18 to 15.95% with fibres) due to the lower degradation of the solid matrix. It also promoted an increase in the difference between elastic and plastic energy (from - 1.04 to 13.92 kJ/m(3) without fibres, and - 1.68 to 10.19 kJ/m(3) for the first cycle).

The application of chemical stabilizers and fibres for the stabilization of weak soil subgrades can mitigate the cost and CO2 emissions associated with pavement construction. The present study evaluates the feasibility of improving clay and sand subgrades using a calcium-based stabilizer (CBS)-commercial name: RBI Grade 81-and synthetic fibre-polyester fibre for building economic and sustainable pavements. Two soils, i.e. silty clay of low plasticity and silty sand, were stabilized and reinforced with independent and combined proportions of the CBS and polyester fibre. The test program included plasticity, compaction, advanced cyclic triaxial (ACT), and California bearing ratio (CBR) tests. The experimental and theoretical resilient moduli were determined using ACT and CBR tests, respectively. Subsequently, scanning electron microscopy and X-ray diffraction tests were then conducted to assess the microstructural and mineralogical changes in the soils due to the stabilization and reinforcement. Flexible pavements were designed with experimental and theoretical resilient modulus (MR). A good correlation was developed between the CBR and experimental MR. The results of the study demonstrate a significant overestimation of MR by the theoretical method. It was seen that with up to 186% higher CBR, 228% higher experimental MR, 96% higher theoretical MR, 230% higher traffic benefit ratio, 22% savings in construction cost, and 24% reduction in greenhouse gas emissions, the stabilized soils exhibited superior performance. The study thus demonstrates that the CBS combined with polyester fibre can be used for economical and sustainable pavement construction.