IV. Mass Movement
4.1.Classification of Mass Movement
(1)US Highway Research Committee Classification
(2) Classification based on movement rates
4.2.Mechanisms Responsible for Mass Movement
4.3.Mass Movement as Hazards
1.Expensive soils
2.Creep and Solifluction
3.Flows
4.Landslides
Causes of landslides
External causes
External processes that increase the odds of a slope failure include:
(1)steepening the slope;
(2)removing support from low on a slope; as by stream or ocean-wave erosion;
(3)adding mass high on a slope, as in sediment depositon.
(4)Human triggering landslides, such as removing material from the base of the slope to widen or clear a road; fill dirt on hill slopes to make more view lots.
Internal causes
Internal causes of slope failure include:
(1)inherently weak materials
(2)water weakens earth materials: it does so by its:
(a)weight-increase driving masses of slope materials;
(b)water absorbed by clay minerals so that the shear strength of soil reduces;
(c)decreasing the cohesion of rocks;
(d)subsurface erosion, initiation piping or tunnels;
(e)increase pore-water pressure of materials.
(3)decrease in cohesion, e.g., chemical and physical weathering.
(4)adverse geologic structure, e.g. ancient slide surface, ancient faults, etc.
Triggers of slope failure
(1)Heavy rains,
(2)Earthquake,
(3)Human construction,
5.Snow Avalanches
6.Subsidence