# Performance Evaluation of Laetitic Subgrade Soil Treated with Lime and Coir Fibre-Activated Carbon
## 3 Test Results and Discussion
### One-Dimensional Consolidation  
Figure 9 illustrates the \(\mathrm{e-\log P}\) curves and shows that adding 3% ACF and 12% lime has improved the swelling and compression factors. The compression index (C\({}_{\mathrm{C}}\)) has declined by 51% and 78% with the addition of 3% ACF and 12% L, respectively. The interaction of released clay silica and alumina with free additive ions linked the soil particles together in the pore water, improving compressibility. Similar behaviour was seen by [71] when conducting 1-D oedometer tests on soil stabilised lime; lime decreases the void ratio of treated soil. The cementitious gels fill the gaps and voids in the soil structure and significantly reduce the void ratio. Moreover, smaller particles in the AC can minimise the compressibility of parent soil by filling the voids [39].  
Figure 8: Deformability index (I\({}_{\mathrm{D}}\)) and elastic modulus (E\({}_{50}\)) of lateritic soil and treated soil.  
Figure 9: Compressibility curves (\(\mathrm{e-\log P}\)).  
Figure 10 indicates the void ratio versus consolidation coefficient (C\({}_{\text{v}}\)) for optimum contents and untreated soil. As can be seen, the stabilised specimens have lower void ratios and, hence, less permeability than untreated soil at the same effective vertical stress. This decline in the void ratio of the stabilised specimens is due to AC and lime, which significantly reduces air pockets' volume among soil particles throughout the compaction [72]. Adding 3% ACF reduces the porosity of the non-stabilised soil due to activated carbon is contained small particles with high surface area [73]. However, the C\({}_{\text{v}}\) reduces in lime-treated soil more than in AC specimens. The reduction in C\({}_{\text{v}}\) values results from the change in the soil structure due to the hydration and pozzolanic processes between soil particles, resulting in a dense and compact mixture. Hence, the lower the C\({}_{\text{v}}\) value within the soil, the less permeability was found [74].  
Figure 11 shows the influence of lime and AC on the permeability coefficient (k) of lateritic soil. The k values for both modified and unmodified soil samples were determined at all stress levels, and specimens were kept saturated in the oedometer cell. However, [PERSON] et al. [75] recommended calculating the impact of binder content on the permeability coefficient at the highest applied pressure (800 kN/m\({}^{2}\)). As expected, the permeability of original soil samples is comparatively high (5.40 \(\times\) 10\({}^{-8}\) m/s), whereas that in treated specimens decreases to 2.90 \(\times\) 10\({}^{-8}\) m/s and 6.76 \(\times\) 10\({}^{-9}\) m/s for 3% ACF and 12% lime, respectively. Hydraulic conductivity is a measure of how easily water can flow through interconnected soil voids. Using materials in highway construction depends on the degree of permeability that is effective in the drainage of the pavement system. In this study, AC fills the voids in the stabilised specimen, restricts water, and enhances bonding with the soil particles. Moreover, the free cations of AC interact with the adsorbed clay mineral cations, causing the diffused water layer covering clay particles to shrink. However, lime fills the voids and gaps with cementation gels during curing time and obstructs water flow [76].  
According to Figure 11, the hydraulic conductivity decreases by adding 3% ACF and 12% lime. Compared to untreated soil, the hydraulic conductivity declined about 85% and 26% in lime-treated soil and AC specimens. The hydraulic conductivity would decrease as the curing time in the lime-treated specimen was extended, and more cementitious compounds were produced to fill the voids. Higher lime content causes more cementiation bonding, making specimens stiffer and demanding more pressure to reach, yielding strength and starting particle displacement [77].  
Figure 10: Consolidation coefficient.