## 3 Results and Discussion  
The results of the Afterberg limits tests conducted in the soil samples having different percentages of the stabiliser addition are shown in Figure 5a. As expected, the addition of the stabilizers has substantial influence on the plasticity of the soil contributing to a reduction in the liquid limit and an increase in the plastic limit, albeit smaller for the latter. From the three stabilisers, the addition of hydrated lime induces the greatest reduction in liquid limit whereas Portland cement influences the increase in plastic limit to a greater extent. This is illustrated in Figure 5b where the variation in relation to the values obtained for the non-stabilised soil is shown, i.e., positive and negative variation indicates an increase  
Figure 4: EDS spectrum of the unstabilised soil. and decrease in the values, respectively. While both hydrated lime and Portland cement have comparable reduction in plasticity index (PI) the mechanism causing those changes is different. This is likely associated to changes in soil chemistry taking place when the stabilizer is added, i.e., while the onset of pozzolanic reactions (Equation (1)) is present for both stabilisers, the silicon source required to catalyse the reaction is different. In lime stabilization, the silicon mainly results from the breakdown of the clay minerals as hydrated lime has negligible silica content (Table 2). In contrast, in cement stabilization, silicon is available in the form of silicon dioxide (SiO\({}_{2}\)) approximately in the same proportion as calcium oxide (CaO) (Table 2). This also corroborated by the larger reduction of silicon levels observed through EDS testing of the samples treated with the hydrated lime. \[\text{Ca(OH)}_{2}+\text{H}_{4}\text{SiO}_{4}\rightarrow\text{CaH}_{2}\text{ SiO}_{4}\cdot 2\text{H}_{2}\text{O} \tag{1}\]  
The experimental trends reported herein are in line with experimental observations reported for other high plasticity soils in past studies focusing on the effect of lime and cement stabilization (e.g., [28]) on the Atterberg limits. A series of one-dimensional swelling tests were conducted for selected treatment levels of 2% and 4% by weight. The efficiency of the treatment was evaluated for different vertical  
Figure 5: Summary of the results of soil index testing (Attterberg limits) having different levels of added chemical stabilisers (**a**) test results and (**b**) percentage variation of water content in relation to the non-stabilised soil (HL—Hydrated lime, BFS/HL—70/30 blend of ground granulated blast furnace slag and hydrated lime and PC-Portland cement). stress levels in term of its influence in halting swelling, i.e., positive volumetric change. Figure 6 shows a summary of the results obtained. As expected upon inundation the non-stabilized specimen exhibit mainly swelling behaviour except for the largest vertical stress level adopted (i.e., 50 kPa) where compression (consolidation) dominated the soil behaviour. The role of the stabilizer addition in halting swelling (0-25 kPa vertical stress) or reducing compression (50 kPa vertical stress) are better illustrated in Figure 6b. It can be observed that all stabilisers considered, i.e., Portland cement, hydrated lime and a blend of ground granulated blast furnace slag and hydrated lime are effective in reducing swelling and compression. However, the one showing greatest performance for the same level of treatment is hydrated lime at 4% addition on a dry weight basis. Furthermore, while at 4% addition, Portland cement is the least effective pozzolanic stabiliser tested for reducing swelling is the best performer in terms of reducing compression. This could indicate that the chemical processes taking place between the cement and clay are ineffective at reducing the uptake of water into the interlayer space of the silicate clay basal spacing but the pozzolanic reaction products induce some cementation at the particle's contacts that contribute to a reduction of compression behaviour, also observed in the SEM micrographs (Figure 6).