GLOSSARIES - Geotechnical Earthquake Engineering - page 505

Liquidity Index Index used to distinguish quick clays (liquidity index usually greater than 1.0)
from highly desiccated clays (negative liquidity index).
Liquid Limit See Atterberg Limits.
Log-of-Time Method Using data from the laboratory consolidation test, a plot of the vertical
deformation versus time on a semilog graph. The log-of-time method is used to determine the coeffi-
cient of consolidation. Also see Square-Root-of-Time Method.
Moisture Content (or Water Content) The ratio of the mass of water in the soil divided by the
dry mass of the soil, usually expressed as a percentage. Moisture content and water content are syn-
onymous.
Montmorillonite See Clay Minerals.
Nonplastic Soil A granular soil that cannot be rolled or molded at any water content. A nonplas-
tic soil has a plasticity index equal to zero, or the plastic limit is greater than the liquid limit. A non-
plastic soil is known as a cohesionless soil.
Optimum Moisture Content The moisture content, determined from a laboratory compaction
test, at which the maximum dry density of a soil is obtained using a specific compaction energy. Also
see Compaction.
Organic Soil Soil that partly or predominately consists of organic matter.
Overconsolidation Ratio (OCR)

The ratio of the preconsolidation vertical effective stress to the

current vertical effective stress.
Oversize Particles For fill compaction, the gravel and cobble-size particles retained on the 3 4 -in.

or No. 4 (4.75-mm) U.S. standard sieve. Also see Soil Matrix.
Particle Size Distribution The distribution of particles sizes in the soil based on dry mass. Also
known as grain size distribution or gradation.
Peak Shear Strength The maximum shear strength along a shear failure surface.
Permeability The ability of water (or other fluid) to flow through a soil by traveling through the
void spaces. A high permeability indicates that flow occurs rapidly, and vice versa. A measure of the
soil's permeability is the hydraulic conductivity, also known as the coefficient of permeability.
Plasticity Term applied to silt and clay, to indicate the soil's ability to be rolled and molded with-
out breaking apart. A measure of a soil's plasticity is the plasticity index.
Plasticity Index The liquid limit minus the plastic limit, often expressed as a whole number (also
see Atterberg Limits ).
Plastic Limit See Atterberg Limits.
Plastic Soil A soil that exhibits plasticity; i.e., the ability to be rolled and molded without breaking
apart. A measure of a soil's plasticity is the plasticity index. A plastic soil is also known as a cohesive
soil.
Pore Water Pressure See Pore Water Pressure in Glossary 3.
Principal Planes and Principal Stresses See Glossary 3.
Sand Equivalent (SE) A measure of the amount of silt or clay contamination in fine aggregate as
determined by ASTM D 2419 test procedures.
Sand-Size Particles Soil particles that will pass the No. 4 (4.75-mm) sieve and be retained on the
No. 200 (0.075-mm) U.S. standard sieve.
Secant Modulus On a stress-strain plot, the slope of the line from the origin to a given point on
the curve. The data for the stress-strain plot are often obtained from a laboratory triaxial compression
test.
Shear Strength The maximum shear stress that a soil or rock can sustain. Shear strength of soil is
based on total stresses (i.e., undrained shear strength) or effective stresses (i.e., effective shear strength).