# Performance Evaluation of Laetitic Subgrade Soil Treated with Lime and Coir Fibre-Activated Carbon
## 3 Test Results and Discussion
### Unconfined Compression Strength  
Typical failure patterns of untreated and treated soil specimens with AC and lime are shown in Figure 4. The untreated sample has a bulging shape in the failure plane, while treated specimens were sheared in an inclined plane. The findings of [45] are consistent with the failure plane pattern observations of this study.  
The compressive strength of AC and lime specimens is illustrated in Figures 5 and 6. First, the soil was examined for 1%, 2%, and 3% AC content. Then, the soil was examined for 1%, 2%, and 3% AC, and just 0.5% fibre due to using more than 5% decreases the compacted density, reducing soil strength [60]. Moreover, the soil was stabilised with 3%, 6%, 9%, and 12% lime under two and four weeks of curing.  
The soil compressive strength was raised with rising AC and ACF content. For instance, the un stabilised UCS value of 200.87 kPa enhanced to 243.65 kPa, 306.31 kPa, and 545.40 kPa for 1%, 2%, and 3% AC. Moreover, the 0.5% coir fibre combination further improved the UCS of AC-treated soil, as shown in Figure 5. Likewise, [PERSON] et al. [61] found that adding powder-activated carbon enhances soil's UCS value; some previous  
Figure 4: Failure patterns of UCS test: (**a**) lateritic soil, (**b**) AC-treated soil, and (**c**) lime-treated soil.  
Figure 3: Variation in pH value after adding the various percentage of AC and lime.  
research demonstrated that coir fibre enhanced clay soil's bearing capacity, stiffness, and strength [62].  
The UCS values in lime-stabilised soil improved as the lime percentage and cure time increased [63]. With increasing lime content, the pH value of soil is increased, and it facilitates the dissolving of siliceous and aluminous chemicals from the lattice of clay minerals during lime stabilisation processes. Calcium aluminium hydrate and calcium silicate hydrate gels are formed due to calcium ions combined with compounds released from the lattice of clay minerals [50]. The UCS value for four-week specimens improved by 18.94% rather than two-week samples. Even though the overall UCS values in Figure 6 indicate that lime content and curing time improve compressive strength, the effectiveness of 12 per cent lime is remarkable. A minimum UCS of 800 kPa is acceptable for constructing medium and low-volume roads, according to the Malaysia Public Works Department (MPWD) requirement. The percentages lower than 12 per cent could not enhance the soil strength adequately due to a pH value lower than 12.4 [57]. The result obtained in this study is comparable to previous findings, in which lime in clay soil improved UCS value and was resistant to compression [64].  
Figure 5: The compressive strength value of AC- and ACF-treated soil.  
Figure 6: The compressive strength value for different lime contents.  
Figure 7 illustrates that all treated specimens have more strength than untreated soil specimens. It indicates that adding fibre to AC soils enhances soil strength significantly due to fibre promoting interlocking between soil particles and additives [26]. The UCS value in 3% ACF increased by more than 800 kPa, which is the minimum requirement of (MPWD) specifications, while this amount is obtained for 12% of lime after four weeks. [PERSON] et al. [65] observed similar results by including lime and coir fibres in the marian clay soil. They reported enhancement in geotechnical properties such as shear strength parameters, flexibility, and UCS values. [PERSON] et al. (2019) discovered that incorporating wheat straw fibres and lime into soil increased strain-softening behaviour, secant modulus, and shear strength [30; 65]. Adding fibre as reinforcement improves sample ductility and stability [28]. Therefore, according to MPWD, 3% ACF and 12% L were adequate to obtain a minimal UCS value, as shown in Figure 7.