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
Rock fences are effective against
rock falls
Rock bolts are effective against
blocks of rock in danger of sliding
(translational slide)
Retaining walls are effective against
smaller landslides composed of sediment, soil, mud, small rocks
(rotational slide)
Drainage pipes are effective against
most landslides
- where water is important
Gabions are similar to
retaining walls
- protect small rock falls on not very steep slopes
What is scaling and what is it effective against?
prevention method
- knock loose material off slope
- effective against steep rock falls
Netting is effective against
small rock falls
