The line on the plasticity chart that divides clays from silts. Equation of the line is horizontal at PI = 4 to LL = 25.5, then PI = 0.73(LL-20).
Water content at the bounderies between the states of consistency of a soil.
The load per unit area which the ground can safely support without excessive yield.
Bulk Density (\rho)
The density of a material measured in mass per unit volume.
Bulk Modulus (K) of Incompressibility Modulus
THe modulus of elasticity whihc relates a change in volume to the hydrostatic state of stress. It is the reciprocal of compressibility.
Coefficient of Curvature (Cc)
A measure of the curvature of a grain size distribution plot. Well graded sand and gravels have coefficients of curvature between 1 and 3.
Coefficient of Uniformity (Cu)
A measure of the grain size uniformity using the ration of particle sizes D60 to D10
The process of increasing the density of soil (usually fill) by rolling, tamping, vibrating or other mechanical means.
The degree of adhesion between soil particles that can resist deformation or rupture.
The gradual or slow reduction in volume and increase in density of a soil or mass in response to increased load or compressive stress
Critical Void Ratio
The final void ratio at ultimate strength acheived by loose and dense samples of the same soil after shearing.
Degree of Saturation (SR)
The ratio of the volume of eater to the total volume of void space. The value of SR can range from zero for a completely dry soil or 1 (or 100%) for a fully saturated soil.
An increase in the bulk volume during deformation, cause by a change from a close-packed structure to an open-packed structure.
Direct Shear Test
A laboratory test to measure the shear strength of a soil.
Dry Density (\rhod)
The density of a soil when it is completely dry; bulk density divided by 1 + water content.
The strength of a soil when dry as determined by the crushing test.
Effective Size (D10)
The Diameter D10 which corresponds to the percentage, by weight, of grains equal to 10% on the grain size diagram. Ten percent of the particles are finer and 90% are coarser than the effective size.
Effective Stress (\sigma')
The part of the total stress that is due entirely to the solid particles of soil, and represents an excess over the neutral stress or pore water pressure. Effective Stress = Total Stress - pore water pressure.
A soil in which some particle sizes are missing
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 specified distance, barely touch each other but do not flow together when given a sharp blow.
The sudden large decrease of shearing resistance of a cohesionless soil, caused by a collapse of the structure by shock or strain, and associated with a sudden but temporary increase of the pore water pressure. The material is transformed into a fluid.
Graphical representation of the state of stress (normal and shear) on a particular plane inclined at an angle to the major principle stress.
Mohr Coulomb Equation
An equation describing the failure of a material in shear fracture. The rupture line in a Mohr circle can be approximated by this equation
Normal Stress (\sigman)
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.
Erosion by percolating waters or seepage in a layer of subsoil resulting in caving and the formation of tunnels or pipes through which the soluble or granular material is removed.
Plastic Limit (PL)
The lower limit of the plastic state. Water content at which the soil begins to crumble when rolled out into thin threads.
Plasticity Index (PI)
Range in water content between the liquid limit (LL) and the plastic limit (PL). PI = LL - PL.
The percentage of the bulk volume of a rock or soil that is occupied by void space.
The condition of soil in which a decrease in intergranular pressure allows water to flow upwards with sufficient velocity to reduce significantly the soils bearing capacity.
Relative Density (R.D.)
The ratio 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.
The amount of compaction relative to the moisture-density curve, or compaction curve
The movement of water or other fluid through a porous material such as soil.
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 (\tau)
The component of stress that acts along a plane through any point in the body
Water content at which the soil volume is lowest
The ratio of the density of the solid particles to the density of water at 4 deg C.
Change in the shape or volume of a body as a result of stress, defined as the ratio of the change to the original shape.
the force per unit area. The symbol \sigma is used to denote the overall stress as well as the component of stress that acts normal to the plane (normal stress)
The property of a soil that is able to absorb stress by plastic deformation
The most widely used shear strength test in which the drainage conditions can be controlled. Three principal types of tests are: unconsolidated-undrained (UU), consolidated-undrained (CU), and consolidated-drained (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
The line on the plasticity chart that marks the approximate upper limit of the relationship between the plasticity index and the liquid limit for natural soils. It is a check against erroneous - if a data point plots above or to the left of the line, verify the information.
Unit Weight ( \gamma )
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.
A soil with all grain sizes present with no excess in any size-range. Equivalent to the geologist term "poorly-graded"
Young's Modulus (E)
An elastic constant given by the ration of stress to its corresponding strain under given conditions of load, for materials tha deform elastically according to Hooke's Law