# Application of a Geotextile in the Treatment of Post-Subsidence in Karst Areas
## 4 Results and Discussion
### Effects of Anchorage Length of Geotextile
#### 4.1.3 Soil Displacement  
Figure 10 shows the vertical displacement contours of soil for different anchorage ratios of \(L/B\) at the final state of subsidence. The displacement legend is shown at the right side of each displacement contour. The greatest soil displacement exists at the bottom of subsidence area for each image. With the increase of the fill height, the displacement develops towards the stable area and surface displacement occurs. A darker color is shown if the geotextile (See Figure 10a) is not used, meaning the occurrence of greater soil displacement at the bottom of subsidence  
Figure 10: Vertical displacement contours of soil for different buried depths of the geotextile for different anchorage ratios \(L/B\) at the final state of subsidence: (**a**) \(L=0B\); (**b**) \(L=0.25B\); (**c**) \(L=0.35B\); (**d**) \(L=0.5B\); (**e**) \(L=0.75B\); (**f**) \(L=1.0B\). area and greater settlement on the surface as compared to the conditions when using the geotextile. The application of a geotextile can control the vertical displacement of soil and effectively decrease the upward development of subsidence. With a sufficient anchorage length, the vertical displacement contours for the vertical displacement of the soil with the anchorage length of geotextile for \(L=0.5B\), \(L=0.75B\) and \(L=1.0B\) (See Figure 10d-f) are similar, while, for anchorage lengths of \(L=0.25B\), \(L=0.35B\), and \(L=0.5B\) (See Figure 10b-d), the soil displacement at the bottom of the subsidence area decreases with the increase of the anchorage length. It is indicated that a sufficient anchorage length of at least greater than \(0.5B\) can better control the soil displacement due to the tensioned membrane effect of geotextile and ensure stability of the treated structure. Figure 11 illustrates the surface settlement for different anchorage ratios \(L/B\) at the final state of subsidence. Each curve has a peak value of surface settlement at the center of the subsidence area. The surface settlement decreases as the horizontal distance from the center of the subsidence area increases. When the horizontal distance from the center is about 5.5 m, indicating the location inside the stable area, the surface settlement is close to zero. The surface settlement decreases with the increase of the anchorage ratio, meaning that increasing the anchorage length is more beneficial for the treatment of subsidence. The surface settlement results for anchorage lengths of \(L=1.0B\) and \(L=0.75B\) are similar, indicating a similar effect on subsidence treatment. In order to quantify the decrement on surface settlement with the increase of the anchorage length of the geotextile, decrement ratio \(\alpha\) was proposed as per Equation (3). The \(\alpha\) in Equation (3) represents the decrement of surface settlement under different anchorage ratios \(L/B\) (using a geotextile) as compared to \(L/B=0\) (without using a geotextile). \[\alpha\ =\ \frac{X-x}{x}\times 100\% \tag{3}\]  
where \(\alpha\) is the decrement ratio of surface settlement under different anchorage ratios \(L/B\) (using geotextile) as compared to \(L/B=0\) (without using geotextile) as a percentage, \(X\) is the surface settlement under different anchorage ratios \(L/B\) (using a geotextile) in mm, and \(x\) is the surface settlement under the anchorage ratio \(L/B=0\) (without using a geotextile) in mm. Figure 12 shows the decrement ratio of surface settlement under different anchorage ratios \(L/B\) as calculated by Equation (3). It shows that the decrement ratio of surface settlement increases with the improvement of the anchorage ratio of the geotextile, indicating that a greater anchorage length is more beneficial to reducing surface settlement.