Civil Engineering Reference
In-Depth Information
Effective Shear Strength
Shear strength of soil based on effective stresses. The effective shear
strength of soil could be expressed in terms of the failure envelope, which is defined by effective cohe-
sion
c
and effective friction angle
.
Shear Strength in Terms of Total Stress
Shear strength of soil based on total stresses. The
undrained shear strength of soil could be expressed in terms of the undrained shear strength
s
u
, or by
using the failure envelope that is defined by total cohesion
c
and total friction angle
.
Shear Strength Tests (Laboratory)
There are many types of shear strength tests that can be per-
formed in the laboratory. The objective is to obtain the shear strength of the soil. Laboratory tests can
generally be divided into two categories:
Shear Strength Tests Based on Effective Stress
The purpose of these laboratory tests is
to obtain the effective shear strength of the soil based on the failure envelope in terms of effective
stress. An example is a direct shear test where the saturated, submerged, and consolidated soil speci-
men is sheared slowly enough that excess pore water pressures do not develop (this test is known as a
consolidated-drained test).
Shear Strength Tests Based on Total Stress
The purpose of these laboratory tests is to
obtain the undrained shear strength of the soil or the failure envelope in terms of total stresses. An
example is the unconfined compression test, which is also known as an unconsolidated-undrained test.
Shrinkage Limit
See
Atterberg Limits.
Sieve
Laboratory equipment consisting of a pan with a screen at the bottom. U.S. standard sieves
are used to separate particles of a soil sample into their various sizes.
Silt-Size Particles
That portion of a soil that is finer than the No. 200 sieve (0.075 mm) and coarser
than 0.002 mm. Silt and clay size particles are considered to be
fines.
Soil Matrix
For fill compaction, that portion of the soil that is finer than the
3
4
-in. or No. 4 (4.75-
mm) U.S. standard sieve. Also see
Oversize Particles.
Soil Structure
Definitions vary, but in general both the geometric arrangement of the soil particles
and the interparticle forces which may act between them. Common soil structures are as follows:
Cluster Structure
Soil grains that consist of densely packed silt or clay size particles.
Dispersed Structure
Structure in which the clay size particles are oriented parallel to one
another.
Flocculated (or Cardhouse) Structure
Structure in which the clay size particles are oriented
in edge-to-face arrangements.
Honeycomb Structure
Loosely arranged bundles of soil particles having a structure that
resembles a honeycomb.
Single-Grained Structure
An arrangement composed of individual soil particles. This is a
common structure of sands.
Skeleton Structure
An arrangement in which coarser soil grains form a skeleton with the void
spaces partly filled by a relatively loose arrangement of soil fines.
Specific Gravity
The ratio of the density of the soil particles to the density of water. The specific
gravity of soil or oversize particles can be determined in the laboratory.
Square-Root-of-Time Method
Using data from the laboratory consolidation test, a plot of the
vertical deformation versus square root of time. The square-root-of-time method is used to determine
the coefficient of consolidation. Also see
Log-of-Time-Method.
Tangent Modulus
On a stress-strain plot, the slope of the line tangent to the stress-strain curve at
a given stress value. The stress value used to obtain the tangent modulus is often the stress value that
is equal to one-half of the compressive strength. The data for the stress-strain plot can be obtained from
a laboratory triaxial compression test.
Tensile Test
For a geosynthetic, a laboratory test in which the geosynthetic is stretched in one
direction to determine the force-elongation characteristics, breaking force, and breaking elongation.
Texture (of Soil)
The degree of fineness of the soil, such as smooth, gritty, or sharp, when the soil
is rubbed between the fingers.
