# Research on Bidirectional Reservation Method for Anti-Permeation Geomembrane Slack
## 3 Analysis and Comparison of Different Methods
### Cross-Notch-Type Centralized Laying Relaxation Amount Method Analysis
#### 3.1.3 Plastering Program  
From the above formula, it is clear that the number of geomembrane folds generated by untreated cross-recesses is significantly increased. The best method for eliminating folds while bidirectionally reserving the geomembrane is to move the excess geomembrane generated by the recesses from all sides toward the center. Since the excess geomembrane is generated by the presence of cross-intersections, a cross-groove intersection grinding solution is adopted to find the optimum cross-intersection over-angle to substantially eliminate the excess membrane area.  
A field corner-smoothing program (Program II) is conducted to allow the geomembrane to transition smoothly into the cross-recesses without creasing. According to the field test, the upper corners of the sidewalls of the cross-recesses and the four sharp corners at the intersection of the cross-recesses can be smoothed. Among these parts, the upper corners of the sidewalls are the easiest to handle, as they can be polished into rounded shapes. A difficulty of this study is the handling of the four sharp corners at the cross-intersection of the recess.  
After preliminary field tests, we find that grinding the sharp corners of the recesses at the cross-intersections to create a spherical structure, as shown in Figure 6a, can effectively consume the extra concentrated geomembrane at the cross-intersections in the bidirectional recess reservation. As shown in Figure 6b, the number of geomembrane folds at the cross-intersections is significantly reduced. However, the geomembrane folds generated under this solution are still large and cannot guarantee the preservation of the geomembrane impermeability characteristic.  
Figure 5: Calculation model of excess geomembrane in cross-notch bidirectional laying in Program I. (**a**) Geomembrane enters longitudinal groove, (**b**) geomembrane enters transverse groove, (**c**) bidirectional groove laying completed, (**d**) source of folds.  
After wiping the corners and laying the geomembranes several times to evaluate the effects of corner wiping, we found a spherical shape that could remove the concentrated geomembrane folds in the center of the groove cross. The results of the treatment are shown in Figure 6c,d. After measurement, the dimensions of the structure are as shown in Figure 6e,f, with a slope arc of 35\({}^{\circ}\) and a total length of 1.3 m for the diagonal two-arc slope connection, which is approximately 6 times longer than the length of the rectangular diagonal at the cross-intersection before treatment.  
Cross-recesses can meet the requirements of bidirectional geomembrane slack retention. After detailed corner wiping, the four sharp corners at the intersection of cross-recesses were treated as spherical footings with an arc of 35\({}^{\circ}\), and the diagonal length of the footings was expanded 6 times. The cross-recesses can allow the geomembrane slack to enter the recesses approximately without folds, ensuring the safe laying of geomembranes. Therefore, we believe that the optimal wiping angle for the cross-groove-shaped technique is 35\({}^{\circ}\). However, this method of reservation requires two cross-shaped grooves to be excavated at regular intervals, increasing civil construction costs to a certain extent. Moreover, to lay the geomembrane into cross-recesses without excess folding, the cross-intersections of the recesses need to be sharpened, increasing the difficulty of construction.