Environmental Engineering Reference
In-Depth Information
9.1.2
Hazard Recognition
General
Slope failures occur in many forms. There is a wide range in their predictability, rapidity
of occurrence and movement, and ground area affected, all of which relate directly to the
consequences of failure. Recognition permits the selection of some slope treatment which
will either
avoid, eliminate, or reduce the hazard.
Hazard recognition and successful treatment require thorough understanding of a num-
ber of factors including:
Types and forms of slope failures (classification)
●
Relationship between geologic conditions and the potential failure form
●
Significance of slope activity, or amount and rate of movement
●
Elements of slope stability
●
Characteristics of slope failure forms (see
Section 9.2)
●
Applicability of mathematical analysis (see
Section 9.3
)
●
Classification of Slope Failures
A classification of slope failures is given in Table 9.1. The most important classes are
falls,
slides, avalanches
, and
flows
.
TABLE 9.1
A Classification of Slope Failures
Type
Form
Definition
Falls
Free fall
Sudden dislodgment of single or multiple blocks of soil or rock which fall in
free descent
Topple
Overturning of a rock block about a pivot point located below its center of
gravity
Slides
Rotational
Relatively slow movement of an essentially coherent block (or blocks) of soil,
or slump
rock, or soil-rock mixtures along some well-defined arc-shaped failure surface
Planar or
Slow to rapid movement of an essentially coherent block (or blocks) of soil or
translational
rock along some well-defined planar failure surface.
Subclasses
Block glide
A single block moving along a planar surface.
Wedges
Block or blocks moving along intersecting planar surfaces
Lateral
A number of intact blocks moving as separate units with differing displacements
spreading
Debris slide
Soil-rock mixtures moving along a planar rock surface
Avalanches
Rock or
Rapid to very rapid movement of an incoherent mass of rock or soil-rock debris
debris
wherein the original structure of the formation is no longer discernible,
occurring along an ill-defined surface.
Flows
Debris
Soil or soil-rock debris moving as a viscous fluid or slurry, usually terminating
Sand
at distances far beyond the failure zone; resulting from excessive pore
Silt
pressures (subclassed according to material type)
Mud
Soil
Creep
Slow, imperceptible downslope movement of soil or soil-rock mixtures.
Solifluction
See
Shallow portions of the regolith moving downslope at moderate to slow rates in
Section 7.7.3
Arctic to sub-Arctic climates during periods of thaw over a surface usually
consisting of frozen ground
Complex
Involves combinations of the above, usually occurring as a change from one form
to another during failure with one form predominant
