# A Novel Technosol Formulation for Sustainable Landfill Top Covers Using Non-Hazardous Wastes
## 3 Results and Discussion
### Geotechnical Properties
WFS and the mixture 90 WFS/10 WAS showed negligible swelling behavior, evidenced by their zero free swelling values. While smectite is present in WFS, the low proportion of this expandable mineral compared to quartz minimizes its influence on the overall material behavior. Consequently, both WFS and the blend 90 WFS/10 WAS maintain stability, experiencing minimal pressure or volumetric fluctuations with moisture exposure. Among the formulations showing the most favorable compaction conditions, the mixtures 90 WFS/10 WAS and 80 WFS/20 WAS underwent CBR testing to assess their strength properties (Figure 6a). The blend 90 WFS/10 WAS had the highest CBR index (23.2), demonstrating outstanding resistance to deformation under load. This feature holds significant importance in the design of landfill covers, as materials with high CBR values can reliably support loads without excessive settlement. Moreover, the CBR swelling value for the blend 90 WFS/10 WAS was relatively low (0.58%), indicating minimal susceptibility to expansion upon soaking. The mixture 80 WFS/20 WAS displayed a moderately higher CBR swelling value (0.76%), suggesting a slightly increased potential for expansion upon soaking compared to the blend 90 WFS/10 WAS. Therefore, selecting the formulation 90 WFS/10 WAS could contribute to the development of a resilient and sustainable landfill cover capable of withstanding external forces and minimizing deformations. Figure 6: Plots of geotechnical results of the tested mixtures: (**a**) California bearing ratio (CBR) index against density; (**b**) water permeability coefficient plotted as a function of time; and (**c**) linear relationship between shear stress and normal stress data derived from a direct shear test on the blend 90 WFS/10 WAS. The hydraulic conductivity of landfill top cover materials is a critical factor influencing their drainage and overall hydrological performance. WFS has been recognized as a reliable hydraulic barrier material through laboratory and field studies [42; 43]. The blends 90 WFS/10 WAS (k = 1.48 \(\times\) 10\({}^{-6}\) cm s\({}^{-1}\)) and 80 WFS/20 WAS (k = 1.00 \(\times\) 10\({}^{-6}\) cm s\({}^{-1}\)) exhibited relatively low permeability coefficients (Figure 6b), allowing for controlled fluid flow and minimizing the risk of excessive water infiltration that can lead to the bathtub effect. The slightly higher permeability coefficient of the blend 90 WFS/10 WAS offers an additional benefit. It could further enhance drainage efficiency and reduce the likelihood of ponding on the landfill cover surface. Shear strength parameters are important for understanding the Technosol's response to shear stresses and assessing its suitability as a sustainable material to maintain the stability of the landfill top cover, especially in sloped sections. Direct shear testing on the mixture 90 WFS/10 WAS, compacted at its optimal moisture content, revealed a cohesion value of 40 kPa and a friction angle (\(\phi\)) of 30\({}^{\circ}\) (Figure 6c). These parameters indicate a moderate degree of shear resistance, which is generally desirable for landfill cap stability. The cohesiveness of this Technosol can minimize erosion from wind or water runoff, thereby enhancing the impermeability of the cover system. The findings emphasize the significant influence of Technosol compositions on their geotechnical properties. Based on the results described above and summarized in Table 2, it is evident that the formulations 90 WFS/10 WAS and 80 WFS/20 WAS demonstrated superior qualities in terms of strength, deformability, and permeability. The high plasticity, swelling potential, and poor compaction characteristics observed in WAS present significant construction challenges. In contrast, mixtures with higher WFS proportions offer improved compaction and stability. The CBR index and permeability coefficient further elucidate the noteworthy differences in strength and permeability among the mixtures.