GLOSSARIES - Geotechnical Earthquake Engineering - page 510

Normally Consolidated The condition that exists if a soil deposit has never been subjected to an
effective stress greater than the existing overburden pressure and if the deposit is completely consoli-
dated under the existing overburden pressure.
Overconsolidated The condition that exists if a soil deposit has been subjected to an effective
stress greater than the existing overburden pressure.
Piping The movement of soil particles as a result of unbalanced seepage forces produced by percolat-
ing water, leading to the development of ground surface boils or underground erosion voids and channels.
Plastic Equilibrium The state of stress of a soil mass that has been loaded and deformed to such
an extent that its ultimate shearing resistance is mobilized at one or more points.
Pore Water Pressure The water pressure that exists in the soil void spaces:
Excess Pore Water Pressure The increment of pore water pressures greater than hydrostatic
values, produced by consolidation stress in compressible materials or by shear strain.
Hydrostatic Pore Water Pressure Pore water pressure or groundwater pressures exerted
under conditions of no flow where the magnitudes of pore pressures increase linearly with depth below
the groundwater table.
Negative Pore Water Pressure Pore water pressure that is less than atmospheric. An exam-
ple is capillary rise, which can induce a negative pore water pressure in the soil. Another example is
the undrained shearing of dense or highly overconsolidated soils, where the soil wants to dilate during
shear, resulting in negative pore water pressures.
Porosity The ratio, usually expressed as a percentage, of the volume of voids divided by the total
volume of the soil or rock.
Preconsolidation Pressure The greatest vertical effective stress to which a soil, such as a clay
layer, has been subjected. Also known as the maximum past pressure.
Pressure (or Stress) The load divided by the area over which it acts.
Principal Planes Each of three mutually perpendicular planes through a point in the soil mass on
which the shearing stress is zero. For soil mechanics, compressive stresses are positive.

Intermediate Principal Plane The plane normal to the direction of the intermediate principal

stress.

Major Principal Plane The plane normal to the direction of the major principal stress (highest

stress in the soil).

Minor Principal Plane The plane normal to the direction of the minor principal stress (lowest

stress in the soil).
Principal Stresses The stresses that occur on the principal planes. Also see Mohr Circle.
Progressive Failure Formation and development of localized stresses which lead to fracturing of
the soil, which spreads and eventually forms a continuous rupture surface and a failure condition. Stiff
fissured clay slopes are especially susceptible to progressive failure.
Quick Clay A clay that has a sensitivity greater than 16. Upon remolding, such clays can exhibit a
fluid (or quick) condition.
Quick Condition (or Quicksand) A condition in which groundwater is flowing upward with a
sufficient hydraulic gradient to produce a zero effective stress condition in the sand deposit.
Relative Density Term applied to a sand deposit to indicate its relative density state, defined as the
ratio of (1) the difference between the void ratio in the loosest state and the in situ void ratio to (2) the
difference between the void ratios in the loosest and in the densest states.
Saturation (Degree of) The volume of water in the void space divided by the total volume of
voids. It is usually expressed as a percentage. A completely dry soil has a degree of saturation of 0 per-
cent, and a saturated soil has a degree of saturation of 100 percent.
Seepage The infiltration or percolation of water through soil and rock.