Slope failure and slope mechanics

Question 1

Where are landslides capable of occurring?

Answer 1

Any environment with relief

Question 2

Why is there a potential for landslides to increase in the future?

Answer 2

Climate change making the environment hotter and wetter

Question 3

What is the number of global fatal landslides?

Answer 3

4862 between 04-16
95% single slope
75% Asia

Question 4

Why does Asia have such a large number of fatal landslides?

Answer 4

Due to the himalays being an area of high relief and tectonic activity

Question 5

What are the local impacts of slope failure?

Answer 5

Transport links (road, rail)
Infrastructure (oil and gas pipelines, fibre optics, other services)
Commercial and residential property
Environmental impacts (e.g. water quality impacts in lakes and rivers)
Secondary hazards (e.g. flooding , dam creation and outburst floods)

Question 6

What type of landslide will be associated with catastrophic failure?

Answer 6

Rock and debris avalanches

Question 7

What are the characteristics of catastrophic slope failures?

Answer 7

Very rapid with high breakage
Large runout

Question 8

WHat inforamtion about catastrophic slides can be acquired from Lake gunn?

Answer 8

By looking at the age can see if many others occurred in same interval and thus if by the same event
Ubiqutous in the landscape so chnace could happen again from a similar event

Question 9

What are the characteristics of shallo debris flows?

Answer 9

Small
Quick
Channelised
Pick up surface regolith on steep slopes
Fan out when channel ends creating flat even area

Question 10

What must be considered before building on debris flow fans?

Answer 10

The level of activity of the fan

Question 11

How does Hungr et al 2014 classify landslides?

Answer 11

Type of movement and material (doesnt consider velocity)

Question 12

How do peat slides occur?

Answer 12

Water pumped by hydrualic pressure lifts the peat on a fluid layer which then breaks into a slurry with a large runout

Question 13

What are the internal causes of slope instability?

Answer 13

Materials
Weathering
Pore water pressure

Question 14

How can the slope material cause instability?

Answer 14

Soil strength loss in contact with water or strain softening
Fine grain soil strength loss or grain from weathering
Discontinuities

Question 15

What is strain softening?

Answer 15

gradual weakening of material as strain increases

Question 16

What are soil discontinuities characterised by?

Answer 16

Low shear strength (bedding planes)

Question 17

How does weathering cause slope instability?

Answer 17

Physical and chemical weathering of soils causing loss of strength (apparent cohesion and friction)
Slope ripening + soil weakening processes

Question 18

What is apparent cohesion?

Answer 18

Chesion - soil strength under varyin saturation (sucktion - wetter or dryer = failure)

Question 19

What are slope ripening processes?

Answer 19

loss of vegetation, shrink
and swell, desiccation and surface cracking

Question 20

What is the effect of removing toe support?

Answer 20

Imbalance in forces
Oversteepening
Loss of shear resistance by toe removal

Question 21

What are the external causes of slope instability?

Answer 21

Removal of slope support
Increased loading
Transient effects

Question 22

How can pore water pressure make a slope unstable?

Answer 22

Elevated pore-water pressures causing a reduction in effective shear stress

Question 23

What ways can slope support be removed?

Answer 23

Undercutting by water (waves and stream incision)
Washing out of soil (groundwater flows)
Human intervention (e.g. Cutting, excavations, tunnelling and mining )

Question 24

How can the load on a slope be increased?

Answer 24

Natural accumulations of water, snow, talus
Human intervention (e.g. fill, tips, buildings)

Question 25

What transient effects can cause slope instabilty?

Answer 25

Earthquakes and tremors
Shocks and vibrations

Question 26

Where ight undrainrd loading occur?

Answer 26

In clays where water can not escape quickly leading to increased PWP

Question 27

How do earthquakes produce landlsides?

Answer 27

Liquefaction (strength to 0)
Dynamic stresses increase pwp

Question 28

What are the stages of creep?

Answer 28

Stage 1 - moderate increase in displacemnt over time
Stage 2 - shallow increase in displacement
Stage 3 - Failure creep, rapid increase

Question 29

What is used to test landslide mechaisms in the lab?

Answer 29

Dynamic Back-Pressured Shear box

Question 30

What does rate of pwp change impact?

Answer 30

Displacement rate

Question 31

Why is fill used and what was the past problems?

Answer 31

Fill used to flatten off areas for construction problem was usually just material lumped so loose unconsolidated and thus prone to failure (Po Shan ROad Hong Kong 1972)

Question 32

What is liquefaction?

Answer 32

Rapid loss of large proportion of the shear resistance
due to the generation high pore water pressures

Question 33

What will happen instead of liquefaction in drained soils?

Answer 33

Compaction

Question 34

What is the effect of slides in loess deposist?

Answer 34

They will be elongate and wider then they are long lower slope angle

Question 35

What are loess deposist?

Answer 35

Silt rich windblown

Question 36

What is dynamic liquefaction?

Answer 36

the loss of strength and stiffness in a saturated granular material due to an increase in pore pressure that’s caused by vibrations or motion

Question 37

What are the stages of dynamic liquefaction?

Answer 37

Initial shear stress overcomes failure envelope
Rapid excess pore water generation
Dynamic liquefaction and shear surface collpase and drainage
Strenth recovery to dynamic failure envelope