# Interface Behavior Analysis of Different Geomembrane Liner Systems Based on PIV Techniques
## 3 Results and Discussion
### Additional Stress Analysis of Sand  
The additional stress is the incremental stress caused by the load in the foundation. It is the main cause of deformation due to the loss of stability of the foundation. The additional stress distribution of the smooth geomembrane model is shown in Figure 6. From Figure 6, it can be seen that the additional stress of the sand in the smooth geomembrane liner system gradually decreased from the top to the bottom, indicating that the upper load was transmitted downward. The attenuation of the upper load was consistent with the law that the additional stress in the sand decreases with the increase in the buried depth [10]. Figure 4: Effect of rib shapes on \(p\)–\(s\) curves. (**a**) Smooth and strip rib. (**b**) Smooth and block rib. (**c**) Strip and block rib. Figure 5: Influence of rib spacing on \(p\)–\(s\) curves. (**a**) \(h\) = 3 mm. (**b**) \(h\) = 4.5 mm. (**c**) \(h\) = 6 mm. The additional stress distribution of the ribbed geomembrane model is shown in Figure 7. From Figure 7, it can be seen that the additional stress of the sand in the ribbed geomembrane liner system decreased uniformly from top to bottom, indicating that the ribs affected the distribution of additional stress in the sand during the downward transfer of upper load. It can be seen that the additional stress of the model decreased from top to bottom, which accorded with the law of load transfer in the model. Compared with the smooth geomembrane condition, the additional stress of the ribbed geomembrane model was uniform. This was because the ribs produced a vertical component force under the upper load, which could offset the upper load to reduce the load. It made the internal stress distribution of the model change so that the upper load was partly transferred to the bottom. When the ribbed geomembrane liner system was subjected to the upper load, part of the upper load was offset by the vertical upward force generated by the ribs. This changed the additional stress distribution of the sand and avoided the overall instability or reduction of the bearing capacity of the model. Taking the rib height \(h=6\) mm as an example to analyze the effect of the rib spacing \(d\) on the additional stress distribution of the block ribbed geomembrane model (Figure 8), compared with rib spacings of \(d=50\) mm and \(80\) mm, the additional stress of the sand at measuring points 1 and 2 was significantly lower when \(d=60\) mm. The additional stress of the sand at measuring point 3 and the additional stress of the sand with rib spacing \(d=60\) mm were significantly higher than those of other conditions. This showed that when the rib spacing \(d=60\) mm, the ribs blocked the downward movement of sand, reduced the tensile stress on the geomembrane when sand slipped, and improved the overall stability model. When the rib spacing \(d=80\) mm, the additional stress of measuring point 3 and measuring point 2 at the final load were almost the same. This showed that when the rib spacing exceeded a specific value, the overall stability of the model may be destroyed. It was also indicated that there was an optimal value for the rib spacing of the ribbed geomembrane. Figure 6: Additional stress distributions of the smooth geomembrane model. Due to the similar effects of different rib heights on the additional stress of the sand, 80 mm rib spacing conditions were used as an example to analyze the additional stress distribution of rib height on the ribbed geomembrane model. As shown in Figure 9, it can be seen from the figure that when the rib height \(h=3\) mm, the values at measuring points 1 to 3 varied reached maximums. The additional stress of the sand at different measurement points decreased with the increase in the landfill depth. When the rib height \(h=4.5\) mm, from measuring points 1 to 3, there was additional stress of the sand with the increase in the landfill depth. The overall change trends were relatively stable, which showed that the blocks played an active role in bearing the blockage of sand movement.