# A Novel Technosol Formulation for Sustainable Landfill Top Covers Using Non-Hazardous Wastes
## 2 Materials and Methods
### Geotechnical Testing Methods  
Similar to road construction, landfill covers rely on compacted soil layers as a foundation. However, landfill final cover systems are complex engineering structures that demand a more comprehensive testing approach and adherence to specific safety and stability standards. Geotechnical properties required in landfill construction quality plans [22] were determined using standardized laboratory testing methods outlined in American Society for Testing and Materials (ASTM) and International Organization for Standardization (ISO) protocols to ensure reliable and consistent results [23].  
Grain-size distribution analysis for the coarse-grained material (\(\phi\) > 0.075 mm) was conducted using the sieving method outlined in the ASTM D6913 standard [24]. Additionally, the particle size distribution of the fine fraction was determined using the Mastersizer 3000 laser diffraction particle size analyzer. Liquid and plastic limits were measured on the particle fraction smaller than 0.4 mm, following the ASTM D4318 standard [25], providing representative results of the soil's plasticity behavior. The samples were classified according to the Unified Soil Classification System [26], based on grain size analysis and Afterberg limits.  
Compaction properties were assessed using the standard Proctor test, a widely recognized and standardized procedure for determining the maximum dry unit weight (\(\gamma_{\text{dmax}}\)) and optimum moisture content of soils. Compaction curves were determined in accordance with the ASTM D698 standard [27]. Relative density of particles was determined for the particle fraction smaller than 4.75 mm, following the guidelines outlined by the ASTM D854 standard [28]. Void ratio (e) was subsequently derived from the relative density of the particles (G) and the maximum dry unit weight (\(\gamma_{\text{dmax}}\)), as follows:  
\[\text{e}=\text{G}/\gamma_{\text{dmax}}-1\]  
Swelling potential, a critical factor for long-term stability, was evaluated using oedometer tests in accordance with the specifications of the ASTM D4546 standard [29]. This evaluation included both a free swelling test and a swelling pressure test, performed on carefully molded specimens compacted using the standard Proctor method. The California bearing ratio (CBR) test, based on the ASTM D1883 standard [30], assessed the strength and load-bearing capacity of the compacted soil. This test directly measures a strength index for samples compacted at the optimal moisture content identified through the standard Proctor test.  
To determine the hydraulic conductivity of the sample, a permeability test was conducted in accordance with the ISO 17892-11 standard [31], using a triaxial cell with back-pressure saturation. The test involved a laterally confined cylindrical sample subjected to controlled variations in hydraulic load, with water flow measured under both constant and variable loading conditions.  
Finally, the chosen blend, exhibiting the most favorable combination of strength and permeability properties was subjected to a consolidated drained direct shear test following the ASTM D3080 standard [32], at a strain rate of 0.048 to 0.092 mm/min.