Environmental Engineering Reference
In-Depth Information
Grand Banks, Newfoundland
The earthquake of November 1929 (see
Section 11.3.4)
caused a section of the continental
shelf to break loose and subsequently mix with seawater. It moved offshore for a distance
of about 925 km and broke a dozen submarine cables. Geologists called this flow a “tur-
bidity current” (Richter, 1958).
9.3
Assessment of Slopes
9.3.1
General
Objectives
The assessment of an existing unstable or potentially unstable slope, or of a slope to be cut,
provides the basis for the selection of slope treatments. Treatment selection requires fore-
casting the form of failure, the volume of material involved, and the degree of the hazard
and risk. Assessment can be based on quantitative analysis in certain situations, but in
many cases must be based on qualitative evaluation of the slope characteristics and envi-
ronmental factors including weather and seismic activity.
Key Factors to be Assessed
History of local slope failure activity as the result of construction, weather con-
ditions, seismic activity (See
Section 11.3.4),
or other factors, in terms of failure
forms and magnitudes
●
Geologic conditions including related potential failure forms and their suitabil-
ity for mathematical analysis, material shear strength factors (constant, variable,
or subject to change or liquefaction,
Section 9.3.2)
,
and groundwater conditions
●
Slope geometry in terms of the influence of inclination, height, and shape on
potential seepage forces, runoff, and failure volume
●
Surface indications of instability such as creep, scars, seepage points, and tension
cracks
●
Degree of existing slope activity (see
Section 9.1.2)
●
Weather factors (rainfall and temperature) in terms of the relationship between
recent weather history and long-term conditions (less severe, average, and more
severe) in view of present slope activity, stability of existing cut slopes, ground-
water levels, and slope seepage
●
9.3.2
Stability Analysis: A Brief Review
General Principles
Basic Relationships
Stability analysis of slopes by mathematical procedures is applicable only to the evalua-
tion of failure by sliding along some definable surface. Avalanches, flows, falls, and pro-
gressive failure cannot be assessed mathematically in the present state of the art.
Slide failure
occurs when the shearing resistance available along some failure surface in
a slope is exceeded by shearing stresses imposed on the failure surface. Static analysis of
sliding requires knowledge of the location and shape of the potential failure surface, the
