# Research on Bidirectional Reservation Method for Anti-Permeation Geomembrane Slack
## 3 Analysis and Comparison of Different Methods
### Comparison of Different Methods
#### 3.4.2 Comparison between Different Bidirectional Relaxation Allowance Methods  
As shown in Figure 6, when the geomembrane is laid with the bidirectional concentrated cross-groove reservation method, the geomembrane produces relatively small folds when the four corners of the cross-notch intersection are polished to 35\({}^{\circ}\), which does not affect the safety of geomembrane impermeability. Moreover, when the geomembrane is subjected to tensile stress due to changes in environmental factors, the amount of geomembrane reservation hidden in the grooves is lifted to offset the tensile stress. When the tensile stress disappears, the lifted part of the geomembrane is pressed into the grooves under overlying pressure, forming a cycle of sustainable use. However, this method requires a large amount of excavation, increasing construction costs to a certain extent. In contrast, the bidirectional cross-Z-shaped reservation method shown in Figure 6 reduces civil construction work by laying the folded geomembrane directly on the foundation surface without the need for excavation. However, as seen in Figure 7, the Z-shaped intersection is a 6-layer geomembrane that is folded into a cross shape, and geomembrane folds are more serious and should not be solved. Moreover, this bidirectional cross-folding method requires a 180-degree bend of the first folded layer when folding for the second time. However, the  
Figure 8: Test results of “Z” and groove combination type two-way laying. (**a**) One-way groove, (**b**) laying test film. existing neoprene rods on the market cannot meet the 180-degree bend requirement. Once the geomembrane is subjected to tensile stress and the folded layer is separated, the folded layer cannot be restored to its original state when the tensile stress disappears, and it cannot address the subsequent reappearance of the tensile stress. Relative to the first two cases, the geomembrane shown in Figure 8 can meet the requirement of bidirectional reservation of geomembrane slack, as the number of folds produced becomes almost negligible by laying the geomembrane in a concentrated manner with the combined \(Z\)- and groove-shaped method. However, once the cross-Z-shaped folded part is separated, it cannot be restored to its original state after the tensile stress disappears, and the bidirectional slack reservation becomes unidirectional. A comparative analysis of different geomembrane slack reservation methods in both directions is summarized as follows. This technical note does not quantitatively analyze the specific effects of different relaxation amount reservation methods for geomembranes. This technical note only presents a methodology for bidirectional retention of geomembrane relaxation and verifies the feasibility of the proposed new construction method for geomembranes through outdoor testing. Advantages
* Bidirectional cross-groove-shaped method: as shown in Figure 9a, the groove-shaped slack can be restored to its original state after the stress disappears and used continuously. * Bidirectional cross-Z-shaped method: as shown in Figure 9b, the \(Z\)-shaped slack is laid directly on the ground. No trenching is needed, saving civil construction work. * Combined groove- and \(Z\)-shaped method: ] as shown in Figure 9c, compared with the bidirectional cross-groove-shaped method that requires two grooves to be excavated, the combined groove- and \(Z\)-shaped method requires only one groove to be excavated, which saves civil engineering work. k As shown in Figure 9d, the method of combining groove- and \(Z\)-shaped methods has only one notch, there is no sharp corner at the intersection of the two notches. This eliminates the need for edge angle detailing. Disadvantages
* Bidirectional cross-groove-shaped method: ] as shown in Figure 10a, the edge angles of the notches cause the geomembrane to cease, which is undesirable. However, the edge angle of the groove is cumbersome to deal with.