# Effect of Various Proportions of Rice Husk Powder on Swelling Soil from New Cairo City, Egypt
## 3 Results and Discussion
### Geotechnical Characteristics Evaluation after Using RHP  
#### 3.2.1 Effect of RHP on Afterberg Limits  
Smaller ratios of RHP are more efficient in thinning out the PI, but with an increase in the proportion of RHP, the result becomes less efficient. The results of the Afterberg limits of swelling soil with different percentages of RHP are shown in Table 4.  
The variety of LL, PL, and PI with different percentages of RHP are presented in Figure 6. As seen in this figure, the LL decreases as the percentage of RHP increases. Moreover, PL increases with the increase in additives. The LL was reduced from 92% of the parent soil to 89.5%, 87%, and 85% partial replacement of soil with RHP, 5%, 10%, and 15%, respectively. This can be seen as the result of soil particle bonding and dispersal of the clay fraction by RHP, which acts as a binding agent to stick soil particles together. In addition, this may be due to the substitution of soil swelling with RHP, which has a small water attraction capability. The highest LL variation was achieved at 15% of the RHP. For example, 15% of RHP decreased LL versus LL in the control sample. Consequently, 15% \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**S.No.**} & **RHP** & \multirow{2}{*}{**Liquid Limit (\%)**} & \multirow{2}{*}{**Plastic Limit (\%)**} & \multirow{2}{*}{**Plasticity Index (\%)**} \\  & **(\%)** & & & \\ \hline
1 & 0 & 92 & 36 & 56 \\
2 & 5 & 89.5 & 53.8 & 35.7 \\
3 & 10 & 87 & 61 & 32 \\
4 & 15 & 85 & 80.5 & 4.5 \\
5 & 20 & 100 & 53 & 37 \\
6 & 25 & 103 & 60 & 40 \\ Mean value & & 92.75 & 57.4 & 34.2 \\ Standard & & 6.60 & 13.19 & 15.30 \\ deviation & & 44 & 174 & 235 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Effect of stabilizer on Atterberg limits of the studied samples. Figure 5: X-ray diffraction of the studied clay minerals. is considered the optimal percentage of RHP for this study. This is obvious from Figure 6 that up to 5% RHP, the LL reduction is significant enough to become straight. This finding indicates that, above 5%, the LL reduction increases slightly. Therefore, the lowest value and the maximum LL reduction were obtained at 15% RHP. In addition, this figure shows the change in the PL with additive materials. It is clear from the curves that RHP has a substantial effect on the PL of the expansive soil. The PL of the stabilized soil has increased from 36% for parent soil to 53.8%, 61%, and 80.5% for the partial replacement of the soil by 5%, 10%, and 15% RHP, respectively. This increase in the PL means that the soil treated with RHP requires more water to transform it into a semi-solid plastic state. The same behavior was reported by [PERSON] et al. [20]. It is indicated from Figure 6 (PI) that all processed samples showed a decrease in any additive content. The PI has decreased from 56% (extremely high plasticity) to 4.5% (low plasticity), with an RHP increase from 0% to 15%. The increase in PL and a decrease in PI are primarily caused by the flocculation of clay particles and the increasing number of coarse particles in the mixture. The reaction compounds decrease the repulsion forces between clay particles transmitting the flocculated structure with some cementing or bonding, which should have been responsible for the decrease of the free swell and PI. In addition, the reduction in swelling is attributed to the reduction in the thickness of the diffuse double layer (DDL), which results in the flocculation of clay particles. In terms of the order, the reduction in DDL thickness makes the soil skeleton shrink. It causes a decrease in repellent forces, thereby contributing to the flocculation of clay particles, which later became granular or formed hydrogen bonds [38]. The bond is sufficiently strong that van der Waals forces, so there is no interlayer swelling in the presence of water [39]. Only the increased proportion of RHP between 20% and 25% increases the plasticity index.