Environmental Engineering Reference
In-Depth Information
Major factors of classification include:
Movement form
: Fall, slide, slide flow (avalanche), flow
●
Failure surface form
: Arc-shaped, planar, irregular, ill-defined
●
Mass coherency
: Coherent, with the original structure essentially intact although
dislocated, or incoherent, with the original structure totally destroyed
●
Constitution
: Single or multiple blocks, or a heterogeneous mass without blocks,
or a slurry
●
Failure cause
: Tensile strength or shear strength exceeded along a failure surface,
or hydraulic excavation, or excessive seepage forces
●
Other factors to consider include:
Mass displacement
: Amount of displacement from the failure zone, which can
vary from slight to small, to very large. Blocks can move together with similar
displacements, or separately with varying displacements.
●
Material type
: Rock blocks or slabs, soil-rock mixtures (debris), sands, silts, blocks
of overconsolidated clays, or mud (weak cohesive soils).
●
Rate of movement during failure
: Varies from extremely slow and barely percepti-
ble to extremely rapid as given in Table 9.2.
●
TABLE 9.2
Velocity of Movement for Slope Failure Forms
a
Velocity
(m/s)
Movement
Rate
Classification
10
2
Extermely rapid
10
3 m/sec
Avalanches and flows
1
Very rapid
10
−
1
10
−
2
0.3 m/min
10
−
3
Rapid
10
−
4
1.5 m/day
Slides
10
−
5
Moderate
10
−
6
1.5 m/month
Slow
10
−
7
1.5 m/year
10
−
8
Very slow
Creep
0.3 m/5 year
10
−
9
Extremely slow
a
After Varnes, D. J.,
Landslides and Engineering Practice
, Eckel, E. B., Ed., Highway Research
Board Special Report No. 29, Washington, DC, 1958. Reprinted with permission of the
Transportation Research Board.
