Landslides 4

Question 1

relate the type of landslide damage expected from its velocity

Answer 1

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

Question 2

identify signs of an unstable slope

Answer 2

• weak soil
• vegetation (pistol butt trees)
• previous slides
• slope
• climate
• tension cracks
• harbours also risky

Question 3

Landslide disaster scale is called

Answer 3

Landslide Velocity Class
from 1 to 7
- start to worry above a 5

Question 4

Pistol butt trees

Answer 4

curve at the bottom
indicates unstable slope

Question 5

Mitigation starts with

Answer 5

investigation and monitoring
-> expensive! Sometimes it’s cheaper to repair damage than remove the cause

Question 6

Investigation strategies

Answer 6

• Geostatistics
• Geological mapping
• Hazard mapping
• Modelling (using computers to see where it goes)

Question 7

Geostatistics

Answer 7

• frequency and magnitude
• look at historical records to develop stats

Question 8

Geological mapping

Answer 8

• map materials and properties on site

Question 9

Hazard mapping

Answer 9

• used to plan best route for new roads

Question 10

Mitigation strategies (which one is best?)

Answer 10

1. Avoidance -> BEST
2. Prevention
3. Protection

Question 11

Mitigation: Avoidance scenarios

Answer 11

too expensive in almost all cases

Scenarios:
- buying all property in a town
- moving a completed highway
- convincing ppl to leave a family home

Question 12

Mitigation: Prevention methods

Answer 12

do smt to make sure landslides don’t occur (when ppl are there)

1. removal of material
2. stabilizing slopes
3. drainage
4. vegetation

Question 13

Tensioning a rock anchor helps stabilize a slope by ____

Answer 13

increasing shear strength

increase stress perpendicular to plane of weakness = increase normal force/friction

Question 14

Prevention: stabilizing slopes

Answer 14

Undercut slope = apply resisting force at bottom
- retaining walls or gabions
- rock bolts/anchors (increases normal force)

Question 15

Prevention: removal of material

Answer 15

• simple
• too expensive for many situations BUT cheaper than avoidance

-> ex/ knocking rocks down, dynamites

Question 16

Mitigation: Protection

Answer 16

• minimize hazard
• control/armour where landslides go

Question 17

examples of protection methods

Answer 17

• rock barrier
• rock net
• rockfall shed
• rock fences (catch & dissipate energy)
• debris flow retention structures (remove debris from water)

Question 18

Which is cheaper, removal of material or avoidance?

Answer 18

removal of material

Question 19

Debris retention structure is effective against

Answer 19

debris flows

Question 20

Example: mitigation strategies for rotational slide

Answer 20

• retaining wall
• drains

Question 21

Example: mitigation strategies for rock fall + translational slide

Answer 21

• rock net
• rock fence
• rock bolts
• drains

Question 22

Landslides are ___% of all Canadian hazard deaths

Answer 22

24%
$1.5 billion :O

Question 23

about how many deaths worldwide per year?

Answer 23

~5000

Question 24

Removal of material is effective against

Answer 24

most landslides
- but usually the slope is too big

Question 25

Rock fences are effective against

Answer 25

rock falls

Question 26

Rock bolts are effective against

Answer 26

blocks of rock in danger of sliding
(translational slide)

Question 27

Retaining walls are effective against

Answer 27

smaller landslides composed of sediment, soil, mud, small rocks
(rotational slide)

Question 28

Drainage pipes are effective against

Answer 28

most landslides
- where water is important

Question 29

Gabions are similar to

Answer 29

retaining walls
- protect small rock falls on not very steep slopes

Question 30

What is scaling and what is it effective against?

Answer 30

prevention method
- knock loose material off slope
- effective against steep rock falls

Question 31

Netting is effective against

Answer 31

small rock falls