# Dynamic Shear Degradation of Geosynthetic-Soil Interface in Waste Landfill Sites
## 6 Conclusions  
The shear behaviors of waste landfill systems under dynamic (earthquake) loading are significantly influenced by the response of the interfaces that are composed of geosynthetics and soil. A few conclusions were obtained from the present study, as follows:  
1. The new disturbance function parameters, \(A\) and \(Z\), were estimated using a linear regression technique. Parameter \(A\) increased with the increase of the submersion period under the same chemical and normal stress conditions. On the contrary, parameter \(A\) decreased with the increase of the normal stress under the same chemical and submersion conditions. Parameter \(Z\) increased with the increase of the submersion period and the normal stress under the same chemical conditions. 2. Based on the test results and the new disturbance function parameters, the new disturbance function curves that correspond to the chemical conditions were evaluated. For the short-term submersion (30 days), the acid condition causes more vulnerability. For the long-term submersion, the difference in the disturbance function value at a certain deviatoric plastic strain trajectory, \(\xi_{D}\), was more distinct than that of the value after short-term submersion. In all of cases, acidic conditions caused the most vulnerability for the geosynthetic-soil interface for short-term submersion, and the basic conditions caused the most vulnerable for long-term submersion. 3. The variation between the disturbance curves for each submersion period was significant, and the largest variation was under the basic conditions in which 0.3 MPa of normal stress was applied. The variation between the disturbance curves under each normal stress condition was also remarkable, and the largest variation was for the acidic conditions for the 850-day submersion period. 4. The performance of the numerical back-prediction of the cyclic shear stress-strain relationship is based on the numerical interpolation procedures that are suggested in the present study. Based on the experiment data, the DSC parameters were utilized to reproduce the cyclic shear stress according to the loading cycle. The back-prediction result was also verified by a comparison between the predicted data and the measured data, and sound agreements were demonstrated. Furthermore, the compatibility and accuracy of the DSC parameters, \(A\) and \(Z\) were ensured. 5. The proposed methodology can be used in seismic design procedures of a waste landfill. First of all, only a few seismic simple shear tests need to be performed for representative disturbance functions and parameters to be obtained. Then, those parameters can be verified by numerical back-prediction in order to reduce a large number of laboratory tests. If a considerable number of laboratory tests are performed, the guideline of critical shear strain under dynamic conditions shall be suggested in a further study. Figure 15: Verification of the predicted results (360 days submersion, 0.45 MPa): (**a**) basic; (**b**) acid. In the future, it is expected that the numerical back-prediction of the geosynthetic-soil interface will serve as the basis of a fully numerical analysis. The numerical back-prediction is capable of considering the shear stress degradation with a sufficient accuracy to reducing a large number of laboratory tests. Based on the representative parameters which are verified by numerical back-prediction, the estimated shear strain can be used as a criterion under seismic conditions. Test are performed with limited number of factors (such as normal stress, material, chemical aggressors, etc. ), therefore, it is still difficult to suggest typical back-bone curves. Relevant research will be performed in a further study. The present paper was developed in 2014 by Hanseo University as an in-school research support project. [PERSON] and [PERSON] conceived of the theme, and idea, and organized the framework. [PERSON] checked numerical back-prediction. [PERSON] performed the M-PIA tests required for the paper; and [PERSON] wrote the paper.