Subgrade
Encyclopedia
In transport engineering
, subgrade is the native material underneath a constructed road, pavement or railway (US: railroad) track. It is also called formation level.
The term can also refer to imported material that has been used to build an embankment.
, soil cement
, portland cement
or lime
. It is the foundation of the pavement structure, on which the subbase
is laid.
Preparation of the subgrade for construction usually involves digging, in order to remove surface vegetation, topsoil
and other unwanted material, and to create space for the upper layer of the pavement. This process is known as subgrade formation or reduction to level.
The load-bearing strength of subgrade is measured by California Bearing Ratio
(CBR) test, falling weight deflectometer
backcalculations and other methods.
Transport engineering
Transportation engineering is the application of technology and scientific principles to the planning, functional design, operation and management of facilities for any mode of transportation in order to provide for the safe, rapid, comfortable, convenient, economical, and environmentally...
, subgrade is the native material underneath a constructed road, pavement or railway (US: railroad) track. It is also called formation level.
The term can also refer to imported material that has been used to build an embankment.
Construction
Subgrades are commonly compacted before the construction of a road, pavement or railway track, and are sometimes stabilized by the addition of asphaltAsphalt
Asphalt or , also known as bitumen, is a sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleums and in some natural deposits, it is a substance classed as a pitch...
, soil cement
Soil cement
Soil cement is a construction material, a mix of pulverized natural soil with small amount of portland cement and water, usually processed in a tumble, compacted to high density...
, portland cement
Portland cement
Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...
or lime
Lime (mineral)
Lime is a general term for calcium-containing inorganic materials, in which carbonates, oxides and hydroxides predominate. Strictly speaking, lime is calcium oxide or calcium hydroxide. It is also the name for a single mineral of the CaO composition, occurring very rarely...
. It is the foundation of the pavement structure, on which the subbase
Subbase (pavement)
In highway engineering, subbase is the layer of aggregate material laid on the subgrade, on which the base course layer is located. It may be omitted when there will be only foot traffic on the pavement, but it is necessary for surfaces used by vehicles....
is laid.
Preparation of the subgrade for construction usually involves digging, in order to remove surface vegetation, topsoil
Topsoil
Topsoil is the upper, outermost layer of soil, usually the top to . It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs.-Importance:...
and other unwanted material, and to create space for the upper layer of the pavement. This process is known as subgrade formation or reduction to level.
The load-bearing strength of subgrade is measured by California Bearing Ratio
California Bearing Ratio
The California bearing ratio is a penetration test for evaluation of the mechanical strength of road subgrades and basecourses. It was developed by the California Department of Transportation before World War II....
(CBR) test, falling weight deflectometer
Falling weight deflectometer
A falling weight deflectometer, FWD, is a testing device used by civil engineers to evaluate the physical properties of pavement. FWD data is primary used to estimate pavement structural capacity for 1) overlay design and 2) to determine if a pavement is being overloaded. Use includes highways,...
backcalculations and other methods.