GEOTECHNICAL-ENGINEERING-TERMS_unlocked

Void Ratio

The ratio of the volume of void space to the volume of solid substance.

Porosity

The ratio of the volume of voids to the volume of the soil sample or specimen. It is simply the open space between the soil grains.

Degree of Saturation

The ratio of the volume of water in the void spaces to the volume of the voids. It is simply the measure of the void volume that is filled by water, expressed as a percentage ranging from 0 to 100.

Moisture Content

The ratio of weight of water to the weight of solids in a given volume of soil.

Unit Weight

The weight of soil per unit volume.

Dry Unit Weight

The weight per unit volume of soil, excluding water.

Saturated Unit Weight

The bulk unit weight of a soil when it is 100 percent saturated.

Bulk Unit Weight

Known as total, wet or moist unit weight. It is the total weight divided by the total volume.

Critical Hydraulic Gradient

The hydraulic gradient that brings a soil (essentially, Coarse-grained soils) to static liquefaction.

Density

The ratio of the total mass to the total volume of a unit of soil. Usually expressed as a unit weight where weight is interchanged with mass.

Dry Density

The ratio of the mass of the solids (soil grains) to the total unit volume of soil.

Submerged Density

Also known as buoyant density. The difference between the total density and the density of water.

Density Index

Also known as relative density. The density of a granular soil relative to the minimum and maximum densities achieved for that particular soil.

Atterberg Limits

Consistency used to describe the degree of firmness of soil.

Cohesion

The attraction of one water molecule to another resulting from hydrogen bonding (water-water bond).

Adhesion

It involves the attraction of a water molecule to a non-water molecule (water-solid bond).

Stickiness

The capacity of soil to adhere to other objects. It is estimated at moisture content that displays maximum adherence between thumb and forefinger.

Rupture Resistance

A field measure of the ability of the soil to withstand an applied stress or pressure as applied using the thumb and forefinger.

Atterberg’s Limit

The limits of water content used to define soil behavior.

Liquid Limit

The moisture content in percent required to close a distance of 12.7mm along the bottom of the groove after 25 blows. It is defined as the moisture content at which soil begins to behave as a liquid material and begins to flow.

Cup Method To Determine Liquid Limit

The device used in this method consists of a brass cup and a hard rubber. The brass cup is dropped onto the base by a cam operated by a crank.

Plastic Limit

The moisture content at which the transition from Semi-Solid to Plastic state.

Shrinkage Limit

The moisture content at which the transition from Solid to Semi-Solid takes place. It is defined as the moisture content at which no further volume change occurs with further reduction in moisture content.1. Liquidity Index:A ratio that indicates the relative consistency of a cohesive material in its natural state.

Plasticity

The degree to which a soil can be molded or reworked without rupturing, causing permanent deformation.

Consistency Index

The ratio of the difference between the liquid limit and water content to the difference between the liquid limit and the plasticity index.

Plasticity Index

The difference between the liquid limit and plastic limit of a soil.

Shrinkage Index

The difference between the plastic limit and shrinkage limits of a soil.

Residual Soil

Soils formed by the weathered products at their place of origin.

Lacustrine Soil

Soils formed by deposition in quiet lakes.

Alluvial Soil

Soils transported by running water and deposited along streams.

Glacial Soil

Soils formed by the transportation and deposition of glaciers.

Marine Soil

Soils formed by deposition in the seas.

Gravel Soil

Soil with occasional particles of quartz, feldspar, and other minerals.

Aelian Soil

Soils transported and deposited by wind.

Activity

Soil classification defined by the ratio of the plasticity index to the percent of clay size fraction, by weight.

Sieve Analysis

Method used to determine the grain size distribution of coarse-grained soil.

Hydrometer Analysis

Method used to determine the grain size distribution of soils passing the No. 200 sieve.

Effective Size

The diameter in the particle size distribution curve corresponding to 10% finer, used to measure hydraulic conductivity and drainage through the soil.

Particle-Size Distribution Curve

Used to determine various parameters for a given soil, including coefficient of uniformity, coefficient gradation, and coefficient of curvature.

Coefficient of Uniformity

The ratio between the grain diameter corresponding to 60% passing on the curve (D60) divided by the diameter of the 10% passing (D10).

Coefficient Gradation

The ratio between the square of the grain diameter corresponding to 30% passing on the curve (D30) divided by the product of the grain diameter of the 60% passing (D60) and the grain diameter of the 10% passing (D10).

Coefficient of Curvature

A measure of the shape parameter obtained from a grain size distribution curve, represented by CD=(D30)2/D10D60.

Poorly Graded

A type of soil in the particle size distribution curve where most of the soil grains are the same size.

AASHTO System

Soil classification system based on grain size distribution, liquid limit, and plasticity indices, used for subgrades and granular type roads.

USCS System

Soil classification system used in engineering and geology to describe the texture and grain size of a soil, represented by a two-letter symbol.1. Coarse-grained soils:Soils with more than 50% by weight of grains retained on the #200 sieve (0.075mm).

Fine-grained soils

Silt and clay soils. Soils containing particles smaller than No. 200 sieve or 0.075 mm in size according to the Unified Soil Classification System.

Cobbles

According to the USCS Soil Classification, a soil particle whose size is greater than 75 mm is called a cobble.

USDA System

Also called as Textural classification system.

Clay

Soil particles which are finer (smaller) than 0.002 mm in size.

Soil Compaction

Volume change in soils which air is expelled from the voids, but with the water content remaining constant. Compaction may occur due to vibration and self-weight.

Optimum moisture content

The moisture content at which the maximum dry unit weight is attained.

Proctor Compaction Test

The laboratory test generally used to obtain the maximum dry unit weight of compaction and the optimum moisture content.

Permeability

The property of soil which permits the flow of water or other liquids through it, or the ease with which water can flow through it.

Maximum dry density

A soil property obtained in the laboratory from a Proctor test. Density of soil at 100% compaction.

Coefficient of Permeability

The constant of permeability, a factor that indicates if the volume of flow is to be great or small, relative to the ease or difficulty with which water moves through the soil.

Hydraulic conductivity

Also known as the coefficient of permeability. The constant average discharge velocity of water passing through soil when the hydraulic gradient is equal to 1.0.

Transmissivity or Transmissibility

The ability of an aquifer to transmit water through its entire thickness.

Discharge velocity

The quantity of water flowing in unit time through a unit gross cross-sectional area of soil at right angles to the direction of flow.

Constant head test

This is used to determine the coefficient of permeability of coarse-grained soil.

Falling Head Test

This is used to determine the coefficient of permeability of fine-grained soil.

Effective Stress

The sum of the vertical components of the forces developed at the Engineereya.1. Points of contact:The number of solid particles per unit cross-sectional area of the soil mass.

Pore water pressure

The stress induced by water pressure.

Intergranular stress

The stress resulting from particle-to-particle contact of soil.

Total stress

The sum of effective and neutral stress.

Capillary rise

The height to which water will rise above the water table due to negative pore water pressure or capillary action of the soil.

Capillary stresses

Pore water pressures less than atmospheric values produced by surface tension of pore water acting on the meniscus formed in void spaces between soil particles.

Piezometer

An instrument used to measure in-situ pore water pressures.

Flow nets

A combination of a number of flow lines and equipotential lines.

Equipotential line

A line along which the potential head at all points is equal.

Flow line

A line along which a water particle will travel from upstream to the downstream side in the permeable soil medium.

Stress distribution of soil

The distribution of stress within the soil mass.

Boussinesq equation

An equation used to determine the increase in vertical pressure at a particular depth caused by an application of a point load at a given surface.

Compressibility of soil

The increase in stress caused by foundation and other loads compresses a soil layer.

Primary consolidation settlement

The result of volume change in saturated cohesive soils because of the expulsion of water that occupies the void spaces.

Normally consolidated

Type of clay whose present effective burden pressure is the maximum pressure that the soil was subjected to in the past.

Over consolidated

Type of clay whose present effective overburden pressure is the maximum pressure that the soil was subjected to in the past.

Secondary consolidation settlement

The result of the plastic adjustment of soil fabrics.

Immediate settlement

Caused by the elastic deformation of dry soil and of moist and saturated soils without any change in the moisture content.

Compression index

The logarithmic slope of the primary consolidation curve. The slope of the normal compression line and critical state line of the Casagrande Method of consolidation curves.

Swell index

Smaller in magnitude than the compression index.

Coefficient of consolidation

Generally decreases as the liquid limit of soil increases and its range of variation is rather wide.

Overconsolidation ratio

Ratio of preconsolidation pressure to present effective overburden pressure.

Shear strength of soil

The capacity of soil to resist shear.

Shear

The force that causes soil to slide or deform.

Gas

Not a component of the soil mass.

Organic Matter

Not a component of the soil mass.

Minerals

A component of the soil mass.1. Direct Shear Test:The oldest and simplest form of shear test arrangement, used to determine the relationship of shear strength to consolidation stress.

Triaxial Shear Test

One of the most reliable methods for determining shear strength parameters, widely used for research and conventional testing.

Confined aquifer

An aquifer that is contained between two stratifications of low permeability soil or rock.

Unconfined Compressive Strength Test

A laboratory test performed on plastic soils, usually clay, to calculate the undrained shear strength.

Cohesion

The undrained shear strength of a soil, considered to be equal to cohesion.

Undrained shear strength

The shear strength of a saturated soil at a given water content under loading conditions where no drainage of pore water can take place.

Coulomb's equation

An equation relating the shear strength of soil to the normal effective stress on the failure plane.

Deviator stress

The difference between the axial and radial stresses of a triaxial test sample.

Triaxial shear strain

A strain parameter used in the interpretation of triaxial stress test results.

Triaxial stress test

Laboratory tests used to determine the strength characteristics of soils, such as cohesion and angle of internal friction.

Artesian

A condition where the water table piezometric surface lies above the ground level.

Angle of shearing resistance

The ratio of effective shear and normal stresses mobilized at any state prior to failure.

Mohr’s Circle

A graphical representation of stress states in soil mechanics.

Normal force

Force acting normal to the plane of reference.