Glossary GLOSSARY *
Basal plane: The deepest landslide failure surface.
Bedding plane: Generally continuous surfaces in a sedimentary rocks
separating depositional layering.
Bench: A relatively level step or terrace constructed into competent
material during a grading operation for the purpose of securing
fill.
Buttress fill: A mass of compacted fill typically constructed at, and
contiguous with, the toe of a slope or landslide for the purpose
of supporting the slope and preventing landslide movement.
Cation: A positively charged elemental'ion.
Creep: Continuous or intermittent, generally slow, movement induced
by gravitational force or environmental changes resulting in
progressive down-slope translation of the overlying deposits.
Curvilinear: Represented by a curved line;.in this report it refers to the
relationship between soil shear strength and overburden
pressure.
•
Dilated slope: A slope, typically at or near the toe of a landslide, that has
experienced bulging and/or dilational cracking due
displacement and high lateral pressures imposed by the
landslide.
Dip: The maximum deviation from horizontal, or plunge, of a
feature such as a bedding plane or geologic contact.
Driving forces: Forces that act to induce downslope movement of a landslide
or earth mass, such as gravity and hydrostatic forces.
Effective The effective vertical pressure imposed on the soil at a
overburden particular depth as a result of the weight of the overlying
pressure: material. If water pressures are induced by soil deformation
or due to the presence of a groundwater table, those pressures
are subtracted from the total overburden to yield the effective
overburden pressure.
411
* An attempt has been made in preparation of this glossary to cover terms specifically related to PBL with
geotechnical connotation as they are used in the Executive Summary.
GLOSSARY
• (Continued)
Factor of Safety: A number representing a simplified measurement on the
stability of slope. This number is defined as a ratio between
the forces resisting landslide movement (resisting forces) and
those inducing landslide movement (driving forces). The
number approximately defines how close a slope is to
experiencing failure. By defmition, sliding is about to occur
at a factor of safety of 1.0 . By defmition, rupture does not
occur at factors of safety in excess of 1.0, however creep
deformation may occur.
Gravity revetment: A protective embankment constructed along the shore line for
the purpose of protecting land from wave erosion and
providing resistance by gravity and support to adjacent inland
slopes. The surface of a revetment are typically protected with
rocks, riprap, or other material to resist wave forces.
Landward portion The upper or uphill portion of a landslide usually characterized
of the landslide: by a graben or extensional zone.
• Ion: An electrically charged atom(s) or molecule produced by the
gain or loss of electrons from its neutral configuration.
Lime: Calcium oxide; a defmition often used loosely for calcium
hydroxide.
Linearly The condition where a change in one variable induces a direct
proportional: and straight line correlation to a second variable.
Overburden The total vertical pressure at a particular depth resulting from
pressure: the weight of the overlying material.
Parametric An analysis involving the systematic variation of input
analysis: parameters to a particular model in order to identify the
sensitivity and response of that model to the input.
Passive resistance: The resistance to deformation which is developed as a soil
being pushed.
Permeability: The ability of an earth mass to transmit fluids such as water.
Pilot program: An initial, generally small scale, field test designed to confirm
the validity of laboratory data and to explore the feasibility of
full scale application of a process.
. Residual strength: A minimum, steady-state soil shear strength which is attained
after the soil has experienced a relatively large amount of shear
displacement. Residual shear strength is typically achieved
along a continuous, smooth, highly polished failure surface.
GLOSSARY
(Continued)
Riprap: Generally angular and boulder-sized pieces of broken rock
used to protect soil embankments from wave action and
erosion.
Shear: To induce failure within a soil mass by inducing displacement
along a surface.
Shear Movement across a relatively well defined failure surface as a
displacement: result of shearing.
Sheared sample: A sample of an earth material that has been subjected to shear
displacement to the extent that its strength to resist the
shearing action has been fully overcome.
Shear(ing) strength: The ability of a soil to resist shear movements; the limiting
shear stress that a soil can withstand without failing by
rupture.
Slide plane: A surface along which shearing or landslide movement is
• occurring or has occurred.
Soluble: Capable of being dissolved in liquid.
Strength envelope: An envelope or line which defines the shear strength of a soil
as a function of overburden pressure. Rupture occurs when
the shear stress within a soil element reaches the level of the
failure envelope.
Stress: Force per unit area.
Subdrain: An underground drain, typically consisting of a perforated pipe
surrounded by gravel, designed to intercept, collect and
convey groundwater to a channel or other collection point on
the ground surface.
Viscous: A fluid or semi-fluid phenomenon of which the resistance to
flow is dependent upon flow velocity. As the term is used in
this report, it describes the slide material of which the
resistance to shear stress is dependant upon the rate of
deformation.
0