GLOSSARIES - Geotechnical Earthquake Engineering - page 501

Slaking The crumbling and disintegration of earth materials when exposed to air or moisture.
Slaking can also refer to the breaking up of dried clay when submerged in water, due either to com-
pression of entrapped air by inwardly migrating water or to the progressive swelling and sloughing off
of the outer layers.
Slickensides Surfaces within a soil mass which have been smoothed and striated by shear move-
ments on these surfaces.
Slope Wash Soil and/or rock material that has been transported down a slope by mass wasting
assisted by runoff water not confined by channels (also see Colluvium ).
Soil Sediments or other accumulations of mineral particles produced by the physical and chemical
disintegration of rocks. Inorganic soil does not contain organic matter, while organic soil contains
organic matter.
Soil Sampler A device used to obtain soil samples during subsurface exploration. Based on the
inside clearance ratio and the area ratio, soil samples can be either disturbed or undisturbed.
Standard Penetration Test (SPT) A field test that consists of driving a thick-walled sampler
(inner diameter 1.5 in., outer diameter 2 in.) into the soil by using a 140-lb hammer falling 30 in.
The number of blows to drive the sampler 18 in. is recorded. The N value (penetration resistance) is
defined as the number of blows required to drive the sampler from a depth interval of 6 to 18 in.
Strike and Dip Strike and dip refer to a planar structure, such as a shear surface, fault, or bed. The
strike is the compass direction of a level line drawn on the planar structure. The dip angle is measured
between the planar structure and a horizontal surface.
Subgrade Modulus (also known as Modulus of Subgrade Reaction) This value is often
obtained from field plate load tests and is used in the design of pavements and airfields.
Subsoil Profile Developed from subsurface exploration, a cross section of the ground that shows the
soil and rock layers. A summary of field and laboratory tests could also be added to the subsoil profile.
Till Material created directly by glaciers, without transportation or sorting by water. Till often con-
sists of a wide range in particle sizes, including boulders, gravel, sand, and clay.
Topsoil

The fertile upper zone of soil which contains organic matter and is usually darker in color

and loose.
Vane Shear Test (VST) An in situ field test that consists of inserting a four-bladed vane into the
borehole and then pushing the vane into the clay deposit located at the bottom of the borehole. Once it
is inserted into the clay, the maximum torque required to rotate the vane and shear the clay is measured.
Based on the dimensions of the vane and the maximum torque, the undrained shear strength s u of the
clay can be calculated.
Varved Silt or Varved Clay A lake deposit with alternating thin layers of sand and silt (varved
silt) or sand and clay (varved clay). It is formed by the process of sedimentation from the summer to
winter months. The sand is deposited during the summer, and the silt or clay is deposited in the win-
ter when the lake surface is covered with ice and the water is tranquil.
Weathering The chemical and/or physical processes by which materials (such as rock) at or near
the earth's surface are broken apart and disintegrated. The material can experience a change in color,
texture, composition, density, and form due to the processes of weathering.
Wetland Land which has a groundwater table at or near the ground surface, or land that is periodi-
cally under water, and supports various types of vegetation that are adapted to a wet environment.

GLOSSARY 2 LABORATORY TESTING
TERMINOLOGY

Absorption The mass of water in the aggregate divided by the dry mass of the aggregate.
Absorption is used in soil mechanics for the study of oversize particles or in concrete mix design.