Description
In areas of extreme debris fall hazard, where roads, railways and other types of structures are built, and stabilization of the slope would be very expensive, construction of a rock shed could be a solution. There exist two alternate configurations depending on the path of the falling debris. Where the debris have a steep trajectory, the shed has a flat roof (Figure 1) covered with a layer of energy absorbing material such as gravel. On the contrary, sheds can have sloping roofs (Figure 2) when they have only to deflect rolling debris without sustaining direct impact leading to a lighter construction and absence of protective layer on the roof. Shed structures are either open ended or completely envelope the rockfall area in a concrete or steel (or other material) structure (Duncan et al., 2004).
Figure 1 Rock shed with flat roof (Google maps)
Figure 2 Rock shed with sloping roofs that deflect rock falls over the railway
(Duncan et al, 2004)
Advantages
- Easy from the access point of view (along a street)
Disadvantages
- Periodical removal of debris material in case of flat roof
Design methods
The design of the gallery depends on the impact force on it and the corresponding penetration depth of the falling rock into the cushion material (Jacquemoud, 1999) when it is required. The impact force is calculated from the fall height, debris size and protective layer properties.
In Figure 3, a scheme with the principal components of the shed is shown.
Figure 3 Principal components of a shed
(Yoshida et al, 2007)
In the design and construction phases, the ductility requirements of the structure and the cushion layer laid on the structure should be considered; at the same time, it is necessary to find a lightweight, economical and better damping material, which reduces the impact forces on the structure, thereby improving the design
The design load is dependent upon the characteristics of the cushion material, input parameters from the rock, topography and the accepted risk involved in the event (Chikatamarla et al.,2004).
Figure 4 Sketch of a rockfall on a protection structure, in flat roof shed typology
(Chikatamarla et al., 2004)
Functional suitability criteria
Type of movement |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Fall | 10 | Will be updated soon |
| Topple | 8 | |
| Slide | 5 | |
| Spread | 2 | |
| Flow | 6 | |
Material type |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Earth | 4 | Will be updated soon |
| Debris | 8 | |
| Rock | 9 | |
Depth of movement |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Surficial (< 0.5 m) | 9 | Will be updated soon |
| Shallow (0.5 to 3 m) | 9 | |
| Medium (3 to 8 m) | 5 | |
| Deep (8 to 15 m) | 3 | |
| Very deep (> 15 m) | 1 | |
Rate of movement |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Moderate to fast | 9 | Will be updated soon |
| Slow | 7 | |
| Very slow | 5 | |
| Extremely slow | 2 | |
Ground water conditions |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Artesian | 7 | Will be updated soon |
| High | 7 | |
| Low | 7 | |
| Absent | 8 | |
Surface water |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Rain | 7 | Will be updated soon |
| Snowmelt | 7 | |
| Localized | 7 | |
| Stream | 3 | |
| Torrent | 3 | |
| River | 2 | |
Reliability and feasibility criteria
| Criteria | Rating | Notes |
|---|---|---|
| Reliability | 8 | Will be updated soon |
| Feasibility and Manageability | 8 | Will be updated soon |
Urgency and consequence suitability
| Criteria | Rating | Notes |
|---|---|---|
| Timeliness of implementation | 3 | Will be updated soon |
| Environmental suitability | 4 | will be updated |
| Economic suitability (cost) | 3 | Will be updated soon |
References
- Rock Slope Engineering, Civil and mining - 4th edition in 2004, Duncan C. Wyllie and Christopher W. Mah.
- The Landslide Handbook— A Guide to Understanding Landslides - Appendix C, Introduction to Landslide Stabilization and Mitigation - Lynn M. Highland, Peter Bobrowsky
- Rock fall sheds - Application of japanese design in North America – First North American landslide conference - H. Yoshida, T. Numura, D. C. Wyllie, A. J. Morris. 2007
- Swiss guideline for the design of protection galleries: background, safety concept and case histories - Joint Japan-Swiss Scientific Seminar on Impact Load by Rock Falls and Design of Protection Structures, Kanazawa, Japan -J. Jacquemoud. 1999
- Rockfall impact on protection galleries - R. Chikatamarla, J. Laue, S.M. Springman. 2004
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