Landslides 4 Flashcards
relate the type of landslide damage expected from its velocity
7 (5m/s) - buildings destroyed, many lives lost
6 (3m/min) - some lives lost
5 (2m/hr) - evacuation possible, structures destroyed
4 (13m/month) - temporary structures can be maintained
3 (2m/yr) - construction can be taken during the movement
2 (16 mm/yr) - some permanent structures undamaged
1 - imperceptible
identify signs of an unstable slope
- weak soil
- vegetation (pistol butt trees)
- previous slides
- slope
- climate
- tension cracks
- harbours also risky
Landslide disaster scale is called
Landslide Velocity Class
from 1 to 7
- start to worry above a 5
Pistol butt trees
curve at the bottom
indicates unstable slope
Mitigation starts with
investigation and monitoring
-> expensive! Sometimes it’s cheaper to repair damage than remove the cause
Investigation strategies
- Geostatistics
- Geological mapping
- Hazard mapping
- Modelling (using computers to see where it goes)
Geostatistics
- frequency and magnitude
- look at historical records to develop stats
Geological mapping
- map materials and properties on site
Hazard mapping
- used to plan best route for new roads
Mitigation strategies (which one is best?)
- Avoidance -> BEST
- Prevention
- Protection
Mitigation: Avoidance scenarios
too expensive in almost all cases
Scenarios:
- buying all property in a town
- moving a completed highway
- convincing ppl to leave a family home
Mitigation: Prevention methods
do smt to make sure landslides don’t occur (when ppl are there)
- removal of material
- stabilizing slopes
- drainage
- vegetation
Tensioning a rock anchor helps stabilize a slope by ____
increasing shear strength
increase stress perpendicular to plane of weakness = increase normal force/friction
Prevention: stabilizing slopes
Undercut slope = apply resisting force at bottom
- retaining walls or gabions
- rock bolts/anchors (increases normal force)
Prevention: removal of material
- simple
- too expensive for many situations BUT cheaper than avoidance
-> ex/ knocking rocks down, dynamites
Mitigation: Protection
- minimize hazard
- control/armour where landslides go
examples of protection methods
- rock barrier
- rock net
- rockfall shed
- rock fences (catch & dissipate energy)
- debris flow retention structures (remove debris from water)
Which is cheaper, removal of material or avoidance?
removal of material
Debris retention structure is effective against
debris flows
Example: mitigation strategies for rotational slide
- retaining wall
- drains
Example: mitigation strategies for rock fall + translational slide
- rock net
- rock fence
- rock bolts
- drains
Landslides are ___% of all Canadian hazard deaths
24%
$1.5 billion :O
about how many deaths worldwide per year?
~5000
Removal of material is effective against
most landslides
- but usually the slope is too big
