Landslides Flashcards
what is mass wasting?
movement of earth material down slope under influence of gravity, occurs in different materials (unconsolidated aka sediment/soil or consolidated aka rocks); causes damage to lives/property
landslides are most common where? when?
-hilly or mountainous regions
-rainy periods
why mass movement occur?
shear force (friction) is overcome due to angle that materials is on
mass movements are classified based on 3 things
1) nature of materials
2) nature of movement
3) speed of movement (1mm/year to 5m/sec)
what is the common system used to classify rocks?
cruden and varnes classification (classified based on type of movement and type of material); bedrock (cohesive) vs soil (unconsolidated)
falls (def.)
rapid free fall, rolling, bouncing (m/min to m/sec)
topples (def.)
rapid rotation of mass around a point
slides (def.)
movement along one or more surfaces (rotational aka slumps or curved failure plane vs translational aka planar failure plane)
lateral spread (def.)
lateral movement of ground, usually with subsidence (sinking of ground)
flows (def.)
viscous fluid movement, range from slow to fast
complex (def.)
combination of two or more types
what can weaken slopes?
coal mining
dumping garbage (adding weight)
construction at crest (adds weight)
storm sewers that add water onto slope
how do rock avalanches happen? what are they?
large material flows rather than slides; typically triggered by earthquake; can travel hundreds of km/hr
-happens when steep system + disturbance trap air, water and gas = created slush that flows like liquid
what is soil creep?
slowest unconsolidated mass movement (1-10 mm/yr); volumetrically the largest
-very slow deformation of surface debris aka regolith, upper layers move down slope faster than underneath layers
what cause soil creep?
freeze-thaw cycle & dry-wet cycle with loose soil & bedrock
hallmarks of soil creep
bent rock layers, bent tree trunks
what is solifluction?
Solifluction occurs in cold climates when water in the
surface layers of the soil alternately freezes and
thaws. When the surface thaws, the soil becomes
waterlogged, yet the water cannot seep downwards.
As a result, the soil becomes so saturated that it
oozes downhill, carrying broken rocks and debris
with them.
Preventative Measures for mass movements
1) slope angle reduction, decrease weight (reduce shear stress)
2) building retention structures
3) leaving stabilizing vegetation
4)decreasing water/pore pressure in soil
5) vertical piles/support walls/rock bolts
6) building outside danger zone
one way to reduce pore pressure
improved drainage
