Landslides

Question 1

what is mass wasting?

Answer 1

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

Question 2

landslides are most common where? when?

Answer 2

-hilly or mountainous regions
-rainy periods

Question 3

why mass movement occur?

Answer 3

shear force (friction) is overcome due to angle that materials is on

Question 4

mass movements are classified based on 3 things

Answer 4

1) nature of materials
2) nature of movement
3) speed of movement (1mm/year to 5m/sec)

Question 5

what is the common system used to classify rocks?

Answer 5

cruden and varnes classification (classified based on type of movement and type of material); bedrock (cohesive) vs soil (unconsolidated)

Question 6

falls (def.)

Answer 6

rapid free fall, rolling, bouncing (m/min to m/sec)

Question 7

topples (def.)

Answer 7

rapid rotation of mass around a point

Question 8

slides (def.)

Answer 8

movement along one or more surfaces (rotational aka slumps or curved failure plane vs translational aka planar failure plane)

Question 9

lateral spread (def.)

Answer 9

lateral movement of ground, usually with subsidence (sinking of ground)

Question 10

flows (def.)

Answer 10

viscous fluid movement, range from slow to fast

Question 11

complex (def.)

Answer 11

combination of two or more types

Question 12

what can weaken slopes?

Answer 12

coal mining
dumping garbage (adding weight)
construction at crest (adds weight)
storm sewers that add water onto slope

Question 13

how do rock avalanches happen? what are they?

Answer 13

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

Question 14

what is soil creep?

Answer 14

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

Question 15

what cause soil creep?

Answer 15

freeze-thaw cycle & dry-wet cycle with loose soil & bedrock

Question 16

hallmarks of soil creep

Answer 16

bent rock layers, bent tree trunks

Question 17

what is solifluction?

Answer 17

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.

Question 18

Preventative Measures for mass movements

Answer 18

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

Question 19

one way to reduce pore pressure

Answer 19

improved drainage