slumping and sliding Flashcards
What factors affect the stability of slopes?
slope angle
- steeper slope: less stable
- stability depends on nature of materials
- gravity> friction= slope will fail
angle repose- maxium angle at which material is stable. the angle is measured to see the max angle
coarse grains: steep angle
fine grains: low angle
coarse grain= increases angle or repose
finer= lower angle of repose
water content
- high pore water pressure reduced resistance to failure- cohesion
- adds weight to slope
- lubricates bedding planes
- small amount of water acts as cohesion force. too much water and cohesion force is gone. this triggers it to fall
vegetation
- helps stabilize slopes
earthquakes
- often trigger failure
slope modification
- building, mining, deforestation
How can slopes be stabilized?
drain water
- add drainage pipes. if water is stopped, it adds weight and can make it fall. drainage pipes allow for water to reduce weight
- lower water table of reservoirs
reduce slopes
- make road cuts in stable positions
-use rock bolts to secure surface laters. this does what a tree/roots would do
what is mass movement
- the downslope movement of rocks or soil material under the influence of graviy
- can cause significant loss of life and property
- ex. saguenay river, quebec
- ex. frank slide, alberta. buried the town of frank
- ex. st jude, quebec, landslide killed a family of 4
- ex. aberfan, wales; coal spoil heap failed
types of mass movement
slumps, falls, and slides:
- material moves downslope as a coherent unit
- moves as one whole unit
-types: slump, fall, rockfall (debris slide),
flows
- material deforms
- types: debris flow, mudflows/mudslides, solifluction and creep, debris avalance, quickclays,
debris flow
- downslope movement of unconsolidated material
- move at rates of meteres to kilometers/hour
- often trigered by heavy rain, spring thaw
- often an assortment of sediment size
mudflows/mudslides
- debris flows with high water content
- can travel up to 10km/hr
- common in volcanic and arid areas
solifluction and creep
- movement of few mm to cm/year
- common in periglacial areas
debris avalanche
- very destructive flows
- move at speeds of over 400km/hour
- often triggered by earthquakes
- ex. yungay, peru 1970, killed 17,000
- common in high mountain environments
quickclays
- silts and clays deposited in glaciomarine setting
- salty porewater is leached out by groundwater
- clay becomes weak and easily fails
- common in coastal areas covered by sea during past glacial episodes
- ex. ottawa region- champlain sea
- ex. rissa nowway; ask, norway. rissa landslide in dec 2020 killed 7 and 3 missing
-ex. quickclays in eastern canada: 1993 lemieux quick clay slide. 3 million m3 sand silt and clay; blocke river. triggered by heavy rainfal high water table
slump
- downslope and outward rotational movemnt of rock or soil
- moves as a unit or a “block”
- often associated with earthquakes and heavy rains
fall
- free fall of single block or large mass from cliff or steep slope
- goes down with gravity
rockfalls (debris slide)
- sudden downslope movement of detached masses of bedrocks (other ones were just sediment in general this is specifically bedrock)
- often occurs on dipping surfaes
- builds talus
- ex. frank slide. alberta
mudflows in rio de janeiro
- favela (shantytowns) have increased in size and number in rio over the last couple of decades
- these are built on unconsolidated material from the erosion of surrounding igenous and metamorphic bedrock
- they are not connected to good proper infrastructire
- the lack of proper infranstructure (ie drainages and proper roads) has caused for the material to become unstable and prone to mudflows
niagra escarptment
- active erosion maintains steep slope
- problems: failures along roadways in hamilton
- hamilton does not have a bylaw against building near escaprtment edge (not like peru which has)
- freeze and thaw cycles. how are joints affected by freeze and thaw cycles
