# Experimental Characterization of the Engineering Properties of Landfill Compost-Biocover
## 2 Materials and Methods
### Methods Employed
#### 2.2.4 Hydraulic Conductivity Tests  
Hydraulic conductivity tests were performed following the procedure described in ASTM D 5084-10 standard [36]. A flexible wall constant head method was employed to determine the hydraulic conductivity of compost materials. First, the compost sample was mixed thoroughly in a mixing pan with a specified quantity of water following the compaction curve. After that, the sample was transferred to a small metallic compaction mold with a 5 cm diameter and 11.5 cm depth, and a small metallic tamper was used to compact the specimen. The specimen was compacted in three equal layers with 30 blows for each layer, adjusted by the trial and error method before starting the test with original samples. The compaction was performed to reach the same dry unit weight and water content as determined in the standard compaction effort (ASTM D 698-07) [34]. The compacted sample was taken out of the mold and trimmed with a sharp knife to remove the anomalies and make it per permeameter specifications. The trimming was also necessary to eliminate the blockage of pores, which occurred due to blows of the tamper at the top surface. Sometimes, the sample was broken into pieces, especially at low water content, and the test had to be repeated. The prepared sample was carefully transferred into a triaxial cell without damaging its edges. The sample was fixed in the test cell with extreme care to eliminate any chances of air inside the cell. The cell was filled with water and connected to a triplex device through the lateral, upper, and lower ports. [PERSON] and [PERSON] [25] reported that the seepage force produces effective stress of 15-20 kPa in a landfill cover. They suggested using a hydraulic gradient of 10 or higher to examine the hydraulic conductivity of landfill cover materials. Thus, a hydraulic gradient of 20 was maintained in this study during the test, adjusting the upper and lower burette of permeater channels. Saturation was achieved by bridging the influent and effluent lines and applying backpressure. Saturation was considered complete after verifying influent intake against effluent water volume supply until they became equal. Furthermore, post-test determination of the degree of saturation for some samples was undertaken to confirm the complete saturation of the samples tested. The head difference was generated in a specimen by adjusting the upper and lower burettes of the channels. After saturation was completed, the upper and lower burettes were bridged to the same pressure for a few minutes to equalize the pressure inside the specimen. A hydraulic gradient was applied to the sample placed in a triaxial cell to determine its permeability. The water level in the upper and lower burettes was recorded at increased time intervals. Finally, an average was taken to obtain accurate results. The same process was repeated for all samples. Figure 3 shows the equilibrium condition for the saturation of the specimen. Equation (1) was employed to determine the hydraulic conductivity of the studied material as in ASTM D 5084-10 standard [36]. \[\mathrm{k}=\mathrm{V(t_{1},t_{2})\cdot L/(P_{B}\cdot A\cdot t)} \tag{1}\]  
In Equation (1), \(\mathrm{k}=\mathrm{hydraulic}\) conductivity (cm/s), \(\mathrm{V(t_{1},t_{2})}=\mathrm{volume}\) of flow from \(\mathrm{t_{1}}\) to \(\mathrm{t_{2}}\) (cm\({}^{3}\)), \(\mathrm{L}=\mathrm{length}\) of sample (cm), \(P_{B}=\mathrm{bias}\) pressure, \(\mathrm{psi}\times\mathrm{70.37}\) cm/psi (cm of \(\mathrm{H_{2}O}\)), \(\mathrm{A}=\mathrm{area}\) of sample (cm\({}^{2}\)), \(\mathrm{t}=\mathrm{time}\) from \(\mathrm{t_{1}}\) to \(\mathrm{t_{2}}\). Replicate samples were prepared at each water content level to ensure the repeatability of test data. Due to the sensitive nature of the specimen, the tests were noticed to be time-consuming. At high water content, the particles of compost materials started to dissolve in water and came out of the sample.