# A Comprehensive Review on Clay Soil Stabilization Using Rice Husk Ash and Lime Sludge
## 3 Laboratory Tests
### California Bearing Ratio (CBR)  
California Bearing Ratio is a laboratory test to evaluate the strength and load-bearing capacity of soils commonly used in geotechnical engineering, particularly in road construction. The compaction process uses a specific compaction effort to achieve the desired density and moisture content representative of the in-situ conditions. Proper compaction at the OMC ensures that the soil is compacted to its optimum condition for bearing capacity and strength, which is crucial for the design and construction of roads, embankments, and other civil engineering structures. The curing period, another significant governing parameter in the CBR test, directly impacts the CBR value obtained. CBR values increase with increasing curing periods, resulting in more accurate representations of the soil performance under the applied loads [119]. The CBR values, as shown in Figure 11, were determined by analyzing the results obtained from different references [109; 120; 121].  
The results of the analysis of the drawn graph from the CBR tests are provided below. Figure 11 illustrates the results of various studies related to the impact of RHA plus LS on  
Figure 11: Effect of RHA and LS in CBR [109; 120; 121].  
the CBR parameters of soil samples. The results indicate that 4% of LS plus RHA content increases the CBR value compared to 8%. It is clear that there is a decrease in the CBR value after increasing the percentage of RHA content above 15%. However, by incorporating both RHA and LS content, the CBR value was increased overall. Higher amounts of LS aim to improve soil properties by increasing CBR, enhancing soil strength and load-bearing capacity, and reducing plasticity, but excessive use of LS can potentially lead to adverse effects if not properly managed.  
The UCS and CBR are both indicators of the strength and load-bearing capacity of soils, but they measure different properties and are deployed for various purposes. CBR is usually more focused on pavement or roadway purposes, while UCS is generally more precise and relevant for clay soils, giving a more fundamental measure of compressive strength for structural purposes such as foundations or slope stability. Hence, the choice depends on the type of project.  
Furthermore, the resilient modulus (M\({}_{\rm r}\)) is a critical parameter in road and pavement applications, as it directly reflects the elastic behavior of soil under repeated loading, which is more representative of the stresses experienced in actual pavement conditions. The CBR test indicates the soil's strength under a static load, making it less suitable compared to Mr for evaluating materials for dynamic conditions like roads. Summarized results from various studies are provided in Table 3.  
The resilient modulus of stabilized clay soils is significantly higher than non-stabilized clay due to the improved soil structure and enhanced bonding mechanisms. In non-stabilized clay, M\({}_{\rm r}\) values are typically low because of the soil's high plasticity, poor particle interlocking, and susceptibility to deformation under repeated loads. Stabilization using materials like RHA and LS initiates pozzolanic reactions, forming CSH, which binds soil particles together and reduces plasticity, leading to a denser, more cohesive matrix with greater resistance to deformation under cyclic loads. Studies have shown that stabilized clay can achieve M\({}_{\rm r}\) values two to five times higher than non-stabilized clay, with values increasing further over time as the curing process continues. This improvement makes stabilized clay more suitable for subgrade applications in road construction.