## 2 Materials and Testing Program  
### Soil  
The soil selected for this study was procured through Road and Maritime Services in conjunction with the Newell Highway Corridor Strategy (NHCS). The samples were taken from the road widening activities and road rehabilitation project located at North Gurley (south of Moree). The main soil properties are given in Table 1. It can be classified as a very high plasticity clay or CV (Unified Soil Classification System). The particle size distribution of the soil is shown in Figure 3 and represents 2% gravel, 35% sand, 60% silt and 2% clay. The fine fraction of the particle size distribution was obtained using laser diffraction technique (Malvern mastersize 3000), which represents the distribution of particles in relation to particle diameter vs. percentage of total particle volume. A technique considering the specific gravity and particles as spheres was adopted to convert from a volume to a mass-based PSD, which introduced some inaccuracies, associated with the approximation of particle shape adopted. While the clay content shown in Figure 3 may be considered unusually small for a soil exhibiting moisture sensitiveness according to well-established expansive soil classifications [20], ref. [21] report that the hydrometer method systematically overestimates the clay fraction respect to the laser diffraction method. Hence, the soil used on this study was classified mainly from a behavioural standpoint. The activity of the soil calculated based on the ratio of the plasticity index and mass percentage of particles smaller than 0.002 mm, was found to be 25.4 which can be classified as very high activity (>1.25) and indicates the soil tested is expansive. Furthermore, the weight plasticity index is 4300 which indicates that this soil has a very high potential for volume change [22]. A summary of the soil index properties is given in Table 1.  
The soil samples were first dried (105 \({}^{\circ}\)C for 24 h) and then the clusters of clay were disaggregated using a mechanical crusher. The soil was then sieved and any particles greater than 2 mm were removed, as to reduce the impact of oversize particles on the swell and shearing of soil specimens, as specified in ASTM D4546. Deionised water and required amount of chemical admixture was added and thoroughly mixed to bring the soil to the required moisture content determined based on its compaction characteristics.  
The soil specimens having the specified water content and chemical admixture were compacted in oedometer rings and shear box mould to the required dry unit weight to meet compaction requirements, e.g., 95% maximum dry unit weight (\(\gamma_{\text{d}}\) = 14.1 kN/m\({}^{3}\)) and 75% of moisture content (w = 20%). However, for the soil specimens used in the swelling tests, a relative compaction of 100% was chosen instead of the minimum of 95%. This is due to the increased swelling experienced at higher compaction levels [23], meaning the critical swelling state will be at a higher level of compaction.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Property** & **Value** \\ \hline Liquid limit (LL) & 73\% \\ Plastic Limit (PL) & 31\% \\ Plasticity Index (PI) & 42\% \\ Mass percentage of particles smaller than 0.002 mm & 2\% \\ Weighted PI = PI \(\times\) \% passing 425 \(\upmu\)m & 4300 \\ Optimum moisture content (OMC) & 27\% \\ Maximum dry unit weight (MDUW) & 14.9 kN/m\({}^{3}\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Summary of the soil properties tested.  
These values were selected to mimic subgrade conditions observed in the field when constructing roads in New South Wales (Australia). The mass of each specimen was recorded, before the samples were sealed with a thin plastic film and kept for 24 h inconstant temperature and humidity conditions for allowing moisture equilibration. Additional material was also prepared for checking moisture content of the soil for verification.