Pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...
is force magnitude applied over an area. Overburden pressure is a geology term that denotes the pressure caused by the
weight
In science and engineering, the weight of an object is a quantity associated with the gravitational force exerted on the object by other objects in its environment, although there is some variation and debate as to the exact definition.
Some sta ...
of the overlying layers of material at a specific depth under the earth's surface.
Overburden pressure is also called lithostatic pressure, or vertical stress.
In a
stratigraphic layer
Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks.
Stratigraphy has three related subfields: lithostrat ...
that is in
hydrostatic
Hydrostatics is the branch of fluid mechanics that studies fluids at hydrostatic equilibrium and "the pressure in a fluid or exerted by a fluid on an immersed body". The word "hydrostatics" is sometimes used to refer specifically to water and o ...
equilibrium; the overburden pressure at a depth z, assuming the magnitude of the gravity acceleration is approximately constant, is given by:
where:
*
is the depth in
meters
The metre (or meter in US spelling; symbol: m) is the base unit of length in the International System of Units (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of of ...
.
*
is the overburden pressure at depth
.
*
is the
pressure at the surface.
*
is the
density
Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...
of the material above the depth
.
*
is the
gravity
In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...
acceleration in
.
In deep-earth geophysics/geodynamics, gravitational acceleration varies significantly over depth and
should not be assumed to be constant, and should be inside the integral.
Some sections of stratigraphic layers can be sealed or isolated. These changes create areas where there is not static equilibrium. A location in the layer is said to be in under pressure when the local pressure is less than the hydrostatic pressure, and in overpressure when the local pressure is greater than the hydrostatic pressure.
See also
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Effective stress
Effective stress is a fundamental concept in soil mechanics and geotechnical engineering that describes the portion of total stress in a soil mass that is carried by the solid soil skeleton, rather than the pore water. It is crucial for understan ...
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Lateral earth pressure
The lateral earth pressure is the pressure that soil exerts in the horizontal direction. It is important because it affects the consolidation behavior and strength of the soil and because it is considered in the design of geotechnical engineering ...
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Pore water pressure
Pore water pressure (sometimes abbreviated to pwp) refers to the pressure of groundwater held within a soil or Rock (geology), rock, in gaps between particles (soil pore, pores). Pore water pressures below the phreatic level of the groundwater are ...
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Sedimentary rock
Sedimentary rocks are types of rock (geology), rock formed by the cementation (geology), cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or de ...
References
Geophysics
Soil mechanics
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