Description
An attenuator system is a type of flexible fence system aimed at decreasing the velocity of falling rocks rather than to capture them, hence to reduce the energy of them by controlling their trajectory during their movement. In this way, the reduction in energy allows the falling rock to be more easily captured by other passive control works situated downward (NZGS, 2016).
Figure 1 On the left: Sketch of attenuator system. On the right: Photo of attenuator systems by GEOVERT
(Rockfall: Design considerations for passive protection structures – 2016)
Disadvantages
- Not easy access, located on high slopes
- It needs a capturing structure downward
Design methods
Attenuators are usually constructed using flexible barrier systems that incorporate a draped net called “tail”. When rocks impact the structure, they continue to travel below the tail, and knocking on the ground, they lose energy with each impact. Attenuator are becoming more widely used as the understanding of their behaviour and performance improves. Currently no published design approaches for attenuators (NZGS, 2016)
In table 1 some design considerations.
Table 1 Design consideration for attenuator system
(NZGS, 2016)
Functional suitability criteria
Type of movement |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Fall | 9 | Will be updated soon |
| Topple | 8 | |
| Slide | 2 | |
| Spread | 1 | |
| Flow | 2 | |
Material type |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Earth | 3 | Will be updated soon |
| Debris | 4 | |
| Rock | 10 | |
Depth of movement |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Surficial (< 0.5 m) | 9 | Will be updated soon |
| Shallow (0.5 to 3 m) | 7 | |
| Medium (3 to 8 m) | 4 | |
| Deep (8 to 15 m) | 2 | |
| Very deep (> 15 m) | 1 | |
Rate of movement |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Moderate to fast | 8 | Will be updated soon |
| Slow | 8 | |
| Very slow | 6 | |
| Extremely slow | 2 | |
Ground water conditions |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Artesian | 8 | Will be updated soon |
| High | 8 | |
| Low | 8 | |
| Absent | 8 | |
Surface water |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Rain | 8 | Will be updated soon |
| Snowmelt | 8 | |
| Localized | 8 | |
| Stream | 3 | |
| Torrent | 2 | |
| River | 1 | |
Reliability and feasibility criteria
| Criteria | Rating | Notes |
|---|---|---|
| Reliability | 7 | Will be updated soon |
| Feasibility and Manageability | 5 | Will be updated soon |
Urgency and consequence suitability
| Criteria | Rating | Notes |
|---|---|---|
| Timeliness of implementation | 6 | Will be updated soon |
| Environmental suitability | 7 | will be updated |
| Economic suitability (cost) | 5 | Will be updated soon |
References
NZGS (2016), "Rockfall: Design considerations for passive protection structure" (https://www.building.govt.nz/assets/Uploads/building-code-compliance/b-stability/b1-structure/rockfall-design-consideration/rockfall-design-passive-protection-structures.pdf)
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