Description
Vegetated slope gratings are made of wooden frame constructed where the slope have failed and backfilled and revegetated to provide an additional support. Not necessarily the framework needs to be made of woods, but also concrete, metal or plastic elements placed on the slope forming parallel or crossed poles can be alternatively used in this technique (Pradhan et al., 2019). In some cases, the construction of gratings may be done by using live cuttings, such as cottonwood posts, by obtaining an additional reinforcement through the development of root network from the cuttings (Schiechtl and Stern, 1996). This measure can be used in areas where erosion occurred, and it needs to be protected from additional erosion. It can be also combined with live crib walls at the toe of the slope for an additional slope support (Florineth et al., 2001).
Advantages:
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Suitable also for very steep slopes (up to 1:1) without the need for slope flattening;
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It requires a very little importation of select backfill and cribfill;
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When filled with earth it covers and protects underlying exposed bedrock from slaking and disintegration;
Disadvantages:
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Slope gratings should be revegetated as soon as possible to achieve a permanent solution;
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A good soil foundation is essential for supporting from the bottom;
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Demanding labour;
Figure 1. Construction of a vegetated slope grating (right picture) based on a vegetated cribwall (left picture) in Karlinbach in 2001 (Florineth et al., 2001).
Design methods
The construction of the frame is made from the bottom. The spacing between horizontal and vertical posts (timber or other material) should not exceed 2 m, creating a square grid not larger than approximately 2 m by 2 m (Figure 2). The squares are then filled with permeable gravel or earth material. Alternatively seeds or living branches together with soil can be placed on the square in order to have a very dense vegetated covering after the establishment period is passed (Schiechtl, 1985). The foundation of the grating is essential for a good support of the structure. Sometimes is useful to implement a live crib wall (Florineth et al., 2001) at the toe of the slope for supporting the vegetated slope grating or otherwise simple poles or timber should be leaned against the slope and connected to each other by horizontally laid cut timber.
Period of installation: when using living cuttings and plants, the construction can only be undertaken during the dormant season. When seeding is used, the best time is the growing season.
Materials: round or square timbers or prefabricated concrete elements are needed fro the gratings, living brances, seeds or cuttings rooted are needed for the covering
Functional suitability criteria
Type of movement |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Fall | 2 | Used to protect an already failed slope from additional erosion. Suited to rotational or pseudo-rotational slides. |
| Topple | 2 | |
| Slide | 9 | |
| Spread | 3 | |
| Flow | 3 | |
Material type |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Earth | 9 | Mainly applicable to landslides involving earth and debris. Applicability in rock limited by typical slope geometry and failure mode. Use of adequate vegetal species is recommended. |
| Debris | 8 | |
| Rock | 4 | |
Depth of movement |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Surficial (< 0.5 m) | 8 | Typically applicable to surficial to intermedite depth landslides. |
| Shallow (0.5 to 3 m) | 8 | |
| Medium (3 to 8 m) | 2 | |
| Deep (8 to 15 m) | 0 | |
| Very deep (> 15 m) | 0 | |
Rate of movement |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Moderate to fast | 1 | Should be carried out preferably on very slow landslides; with due care it can be carried out in slow landslides |
| Slow | 5 | |
| Very slow | 8 | |
| Extremely slow | 6 | |
Ground water conditions |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Artesian | 5 | Applicable in all groundwater conditions. |
| High | 8 | |
| Low | 7 | |
| Absent | 4 | |
Surface water |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Rain | 9 | Mostly applicable for rainwater runoff it is suited also to other surface water conditions. |
| Snowmelt | 9 | |
| Localized | 8 | |
| Stream | 6 | |
| Torrent | 3 | |
| River | 7 | |
Reliability and feasibility criteria
| Criteria | Rating | Notes |
|---|---|---|
| Reliability | 6 | Reliable technique adopted in the case where a landslide already occurred and shallow deposits need to be stabilized. |
| Feasibility and Manageability | 6 | High labour demanding for the installation of the structure along the slope |
Urgency and consequence suitability
| Criteria | Rating | Notes |
|---|---|---|
| Timeliness of implementation | 8 | Relatively short implementation when the material to be used is available on site. |
| Environmental suitability | 10 | When cement or plastic are used for the grating structure, the environmental suitability can be lower. |
| Economic suitability (cost) | 7 | Local material can be provided and the high cost can be only addressed to the labour cost |
References
Florineth, F., Rauch, H. P., & Staffler, H. (2002). Stabilization of landslides with bio-engineering measures in South Tyrol/Italy and Thankot/Nepal. In International Congress INTERPRAEVENT 2002 in the Pacific Rim-Matsumoto/Japan Congress Publication (Vol. 2, pp. 827-837).
Pradhan, S. P., Vishal, V., & Singh, T. N. (Eds.). (2019). Landslides: Theory, Practice and Modelling (Vol. 50). Springer.
Schiechtl, H. M. (1985). FAO Watershed Management Field Manual: Vegetative and Soil Treatment Measures (No. 1-5). Food & Agriculture Org..
Schiechtl, H.M. and R. Stern. 1996. Ground Bioengineering Techniques for Slope Protection and Erosion Control. Trans. By L. Jaklitsch. Blackwell Scientific. Oxford, U.K. 146 pp
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