# Dynamic Shear Degradation of Geosynthetic-Soil Interface in Waste Landfill Sites
## 4 Laboratory Test
### Evaluation of Disturbance Function and Parameters
The antioxidant and other ingredients, such as carbon black, showed evident chemical resistance in the HDPE geonet, as shown in Figure 8. On the contrary, severe surface exfoliation of soil particles was widely observed under acidic conditions and pitting on the soil surface was observed under basic conditions. Therefore, it is concluded that the different damage patterns of soil particles mostly entailed the variation of the disturbance function curves and, accordingly, different \(A\) and \(Z\) parameters were estimated. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Submersion Period (Days)** & **Normal Stress (MPa)** & **Chemical Condition** & **Parameters** & **Avg.** \\ \hline \hline \multirow{8}{*}{30} & & \multirow{4}{*}{Acid} & \(A\) & 1.9269 \\  & & & \(Z\) & 0.4536 \\ \cline{3-5}  & & & \(A\) & 1.7287 \\  & & & \(Z\) & 0.4859 \\ \cline{3-5}  & & & \(A\) & 1.9723 \\  & & & \(Z\) & 0.4768 \\ \cline{3-5}  & & & Acid & \(A\) & 1.8193 \\  & & & \(Z\) & 0.5260 \\ \cline{3-5}  & & & \(A\) & 1.5810 \\  & & & \(Z\) & 0.4972 \\ \cline{3-5}  & & & \(A\) & 1.7989 \\  & & & \(Z\) & 0.5179 \\ \hline \hline \multirow{8}{*}{850} & & \multirow{4}{*}{Acid} & \(A\) & 2.9476 \\  & & & \(Z\) & 0.4852 \\ \cline{3-5}  & & & \(A\) & 2.7061 \\ \cline{3-5}  & & & \(Z\) & 0.5286 \\ \cline{3-5}  & & & \(A\) & 3.2338 \\ \cline{3-5}  & & & \(Z\) & 0.4329 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: \(A\) and \(Z\) parameters. Cyclic simple shear tests on soil alone were performed after prolonged exposure to acidic and basic leachate solutions in order to verify the effect of chemical aggressors on soil. The results were compared with the test results for the geosynthetic-soil interface in Figure 9. Without the interface, basic conditions approached the FA state at the smallest shear strain level, which is the identical trend as the results for the geosynthetic-soil interface. As a result, the disturbance increased more rapidly in the sample without the interface. Figure 10 displays the new disturbance function curves according to the suggested \(A\) and \(Z\) parameters. Based on the newly suggested disturbance function curves, the disturbance variation could be obtained quantitatively. Generally, the disturbance intensified after long-term submersion conditions in all of the cases, however, the difference in the disturbance decreased in the cases of higher normal stress conditions, because the confining effect may resist the abrupt progress of the damage in the geosynthetic-soil interface. The variation of the disturbance curve under each submersion period is significant, and the largest variation was observed under the basic conditions for which 0.3 MPa of the normal stress was applied. Figure 11a shows the maximum decrease of the disturbance under a stress of 0.3 MPa, and Table 4 summarizes the maximum decreases of the disturbance for the results for the 30-day and 850-day submersion periods. In Figure 11b, a log scale for strain axis is applied to exhibit the change in disturbance value at low strain level (<2%), therefore, a log scale chart can be useful in the case that the change of disturbance has mainly occurred at low strain levels. Figure 8: Microscopic observation results (100\(\times\)): (**a**) 850 days submersion, acidic; (**b**) 850 days submersion, basic. Figure 9: Disturbance function curves for soil alone versus with interface after 850 days submersion, 0.3 MPa: (**a**) natural scale; (**b**) log scale.