Slope Stability Analysis and Soil Mechanics

Vocabulary practice flashcards covering key terms, definitions, failure modes, field tests, instrumentation, and seepage principles in slope stability analysis.

Bulking

The volume increase or expansion that occurs when soil is excavated from its natural bank condition into a loose state.

Shrinkage Factor

The net change in soil volume from its original in situ bank condition to its final compacted state.

Natural Slope

A slope that forms part of the natural terrain or topography without human modification.

Cut Slope

A slope created by excavation that exposes natural ground that was previously buried.

Fill Slope

A slope created by placing and compacting earth or rock fill material.

Berm (Bench or Terrace)

A narrow level area created in cut and fill slopes to accommodate surface drainage facilities.

Landslide

The downslope movement of soil, rock, and organic materials under the effects of gravity, as well as the landform that results from such movement.

Landslide Features

The characteristic structural elements of a rotational landslide, including the crown, main scarp, head, surface of rupture, main body, foot, and toe.

Fall

A slope movement beginning with detachment of soil or rock along a surface with little or no shear displacement, where material subsequently descends by falling, bouncing, or rolling.

Topple

The forward rotation out of a slope of a mass of soil or rock around a point or axis located below the center of gravity of the displaced mass.

Slide

A downslope movement of a soil or rock mass occurring on surfaces of rupture or on relatively thin zones of intense shear strain.

Rotational Landslide

A landslide on which the surface of rupture is curved upward (spoon-shaped) and the slide movement is rotational about an axis parallel to the slope contour.

Translational Landslide

A landslide in which the mass moves out, or down and outward, along a relatively planar surface with little rotational movement or backward tilting.

Slump

A rotational slide that features several parallel curved planes of movement.

Lateral Spread

Slope instability occurring on very gentle slopes or flat terrain where a stronger upper layer of rock or soil undergoes extension and moves above an underlying softer, weaker layer.

Flow

A downward movement of soil mass similar to a viscous fluid, in which surfaces of shear are short-lived, closely spaced, and usually not preserved.

Debris Flow

A rapid mass movement in which loose soil, rock, and sometimes organic matter combine with water to form a slurry that flows downslope.

Lahar

A type of volcanic debris flow originating on the slopes of volcanoes that mobilizes loose accumulations of tephra and related debris.

Debris Avalanche

A large, extremely rapid, open-slope flow formed when an unstable slope collapses and the resulting fragmented debris is rapidly transported away.

Slow Earthflow (Creep)

The imperceptibly slow, steady downward movement of slope-forming soil or rock caused by internal shear stress below that required for sudden failure.

Translational Failure

Slope failure that occurs along a weak zone of soil parallel to the slope surface, common in coarse-grained soils and infinite slopes.

Rotational Failure

A mode of slope failure common in homogeneous fine-grained soils characterized by rotation about an imaginary axis parallel to the slope face.

Wedge Failure (Block Failure)

Slope failure occurring when forces shatter a soil mass along joints, cracks, and fissures, causing the fractured material to slide down an angled failure plane in blocks.

Compound Failure

A combination of rotational and translational sliding failure in which the slip surface curves at both ends but has a flat central portion.

Flow Slide

A failure mode in which internal and external factors cause soil to behave like a viscous fluid and flow down modest slopes across poorly defined failure surfaces.

Dynamic Liquefaction

The condition during an earthquake where pore water pressures in saturated coarse-grained soils reach the total mean stress, causing the soil to lose shear strength and behave as a viscous fluid.

Vane Shear Test

An in situ field test used to determine both peak and residual undrained shear strength of clays by inserting a four-bladed device into a borehole and rotating it.

Vibrating Wire Piezometer

A pressure-sensitive submersible measurement sensor installed in a borehole to detect pore water pressure and groundwater levels.

In-Place Inclinometer

A sensor installed in a cased borehole to detect new movement, acceleration, and direction of slope displacement.

Tiltmeter

An instrument used to track and measure changes in slope inclination and vertical rotation on site.

Settlement Plate

A monitoring apparatus used to verify if ground settlement is occurring and measure its rate and magnitude.

Phreatic Surface

The upper line or surface of groundwater seepage within a slope, critical for determining pore water pressures during stability calculations.

Flow Line

A line along which a water particle travels from upstream to downstream within a permeable soil medium.

Equipotential Line

A line along which the potential head at all points within a permeable soil mass is equal.

Flow Net

A two-dimensional graphical mesh formed by intersecting flow lines and equipotential lines, used to calculate seepage rates and pore pressures.

Earth Dam Slopes

The structural slope components of an embankment dam, including the upstream slope adjacent to the reservoir, the downstream slope, and the top roadway.

Varnes Classification of Slope Movements

A system classifying mass movement types (falls, topples, slides, lateral spreads, flows, complex) across bedrock, coarse engineering soils, and fine engineering soils.

Geology, surface drainage, groundwater, soil shear strength

Considerations in Analysis

Bank

An area where excavation will occur.

Crest and Toe of Slope

The points where the slope intersects flatter ground.

Slope Face

The ground surface between top and toe of slope.

Slope Height

Difference in elevation between the top of slope and toe of slope.

Slope ratio

Describes the steepness of the slope and is always expressed as horizontal to vertical.

Unrestrained Slope

an exposed surface that stands at an angle with the horizontal.

Drained Condition

Water is able to flow into or out of a mass of soil as quickly as the soil is loaded Changes in load do not induce changes in pore pressure

Undrained Condition

No flow of water into or out of a mass of soil in response to load changes Variations in load produce changes in pore pressure.

Dutch Cone Test

Used for soil exploration. The cone’s resistance to penetration is determined, as is the sleeve’s frictional resistance.

Piezocone Penetration test

Introduced in the mid-1970s. Measures cone resistance, sleeve friction, and pore pressure.

Rapid Drawdown

The lateral force generated by the water is removed in this scenario, and the excess pore water pressure has little time to dissipate.

Decrease in Shear Strength

Increased pore pressure, cracking, swelling, development of slickenslide, decomposition, creep, leaching, strain softening, weathering, cyclic loading.

Increase in Shear Stress required for Equilibrium

Loads at the top of the slope, water pressure in cracks at the top of slope, Increase in soil weight, Excavation at the bottom, Drop in water level, Earthquake shaking.

Undrained Condition

Rate of Loading is faster than Rate of Drainage.

Drained Condition

Rate of Drainage is faster than Rate of Loading