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Aline
the line on the plasticity chart that divides clays from silts. Equations of the line is horiztontal at PI=4 to LL=25.5, then PI=0.73 (LL20)

Atterberg Limits
water content at the boundaries between the states of consistency of a soil

Bearing capacity
the load per unit area whihc the ground ca safely support without excessive yield

Bulk Density (ρ)
The density of a material measured in mass per unit volume

Bulk Modulus (K) or Incompressibility Modulus
a modulus of elasticity which relates a change in volume to the hydrostatic state of stress.; It is the reciprocal of compressibiltiy

Coefficient of Curvature (C_{c})
a measure of the curvature of the grain size distribution plot. Wellgraded sands and gravels have coefficients of curvature between 1 and 3

Coefficient of Uniformity (C_{u})
A measure of the grain size uniformity using the ratio of particle sizes D_{60} to D_{10}.

Compaction
the process of increasin the density of a soil (usually fill) by rolling, tamping, vibrating or other mechanical means

Consistency
the degree of adhesion between soil particles that can resist deformation or rupture

Consolidation
Gradual or slow reduction in volume and increas in density of a soil mass in response to increased load or compressive stress

Critical Void Ratio
the final void ratio at ultimate strength achieved by loose and dense samples of the same soil after shearing

Degree of saturation (SR)
the raito of the volume of water to the total volume of void space. The value of SR can range from 0 (0%) to 1 (100%)

Dilatancy
an increase in the bulk volume during deformation, caused by a change from a closepacked structure to an openpacked structure

Direct Shear test
a laboratory test to measure the shear strength of a soil

Dry density (ρ_{d})
The density of a soil when it is completely dry; bulk density divided by 1 + water content

Dry Strength
The strength of a soil when dry as determinded by the crushing test

Effective Size (D_{10})
The diameter D_{10} which corresponds to the precentages, by weight, of grains equal to 10% of the grainsize diagram. Ten percent of the particles are finer and 90% are coarser than the effective size

Effective stress (σ')
That part of the total stress that is due entirely to the solid particles of soil, and represents an excess over the neutral stress or porewater pressure. Effective stress = total stress minus porewater pressure

Gapgraded
a soil in which some particle sizes are missing

Hooke's Law
a statement of elastic deformation  the strain is linearly proportional to the applied stress

Liquid Limit (LL)
the upper limit of the plastic state. Water content, in percent of dry weight, at which two sections of a pat of soil, separated by a specific distance, barely touch each other but do not flow together when given a sharp blow

Liquefaction
The sudden large decrease in shearing resistance of a cohesionless soil, caused by a collapes of the structure by shock or strain, and associated with a sudden but temporary increase of the porewater pressure. The material is transformed into a fluid mass

Mohr Circle
graphical representation of the state of stress (normal and shear) on a particular plane inclined at an angle ot the major principal stress

MohrCoulomb Equation
an equation describing the failure of a material in shear fracture. The rupture line is a Mohr circle can be approximated by this equation

Normal stress (σ_{n})
the component of stress that acts perpendicular to the plane

Optimum Moisture Content
the moisture content at which the maximum dry density of a soil is attained

Piping
erosion by percolating waters or seepage in a layer of subsoil resulting in caving and the formation of tunnels or pips through which the soluble or granular material is removed

Plastic Index (PI)
range in water content between the liquid limit (LL) and the plastic limit (PL). PI=LLPL

Plastic Limit (PL)
the lower limit of the plastic state. Water content at which the soil begins to crumble when rolled out onto thin threads

Poisson's Ratio (υ)
An elastic constant (does not exceed 0.5). The ratio of the lateral unit strain to the longitudinal unit strain in a body that has been stressed longitudinally within it's elastic limit

Porosity (n)
The percentage of the bulk volume of rock or soil that is occumpied by void space

Quick condition
the condition of a soil in which a decrease in intergranular pressure allows water to flow upward with sufficient velocity to reduce significantly the soil's bearing capacity

Relative Density (R.D.)
the raito of the difference between the void ratio of a cohesionless soil in the loosest state and any given void ratio to the difference between its void ratios in the loosest and in the densest states
 e_{max}  e = R.D.
 e_{max}  e_{min}

Relative compaction
the amount of compaction relative to the moisturedensity curve, or compaction curve

Seepage
the movement of water or other fluid through a porous material such as soil

Settlement
the gradual downward movement of an engineered structure due to compression of the soil below the foundation

Shear Modulus (G) or Rigidity Modulus
a modulus of elasticity in shear. It measures the shear strain resulting from shear stress on a plane

Shear Strength (s)
the internal resistance of a soil to shear stress consisting of a combination of friction and cohesion

Shear stress (τ)
the component of stress that acts along a plane through any point in the body

Shrinkage Limit
Water content at which the soil volume is lowest

Specific Gravity (G_{s})
the raito of the density of the solid particles to the density of water at 4^{o}C

Toughness
the property of a soil that is able to absorb strees by plastic deformation

Triaxial test
the most widely used shear strength test in which drainage conditions can be controlled. Three principal types of tests are: unconsolidatedundrained (UU), consolidatedundrained (CU), and consolidateddrained (CD)

Unconfined Compressive Strength Test
a special case of the triaxial test in which axial stress is applied to a specimen under atmospheric pressure to obtain the value of the shear strength

Uline
the line on the plasticity chart that marks the approximate uppper limit of the relationship between the plasticity index and the liquid limit for natural soils. It is a check agains erroneous data  if a data point plots above or to the left of the line, verify the information

Unit Weight (γ)
The weight of soil plus water per unit volume

Void Ratio (e)
the ratio of the volume of void space to the volume of solids

Wellgraded
a soil with all grain sizes present with no excess in any size range. Equivalent to the geologist's term "poorly sorted"

Young's Modulus (E) or Modulus of Elasticity
an elastic constant given by the ratio of stress to it's corresponding strain under given conditions of load, for materials that deform elastically according to Hooke's Law

