Pore water pressure
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Pore water pressure refers to the pressure of groundwater held within a soil or rock, in gaps between particles (pores). For example, in a high permeability soil, the pressure would be close to hydrostatic in no flow conditions. It is also referred to as tensiometer pressure.
Pore water pressure (sometimes abbreviated to pwp) is vital in calculating soil strengths in soil mechanics, from Terzaghi's expression for the effective stress of a soil.
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[edit] ISO 11276:1995
BS 7755-5.1: 1996 Soil quality — Determination of pore water pressure — Tensiometer method, which is identical with ISO 11276:1995, defines pore water pressure as
- the sum of matric and pneumatic pressures
[edit] Matric pressure
The amount of work that must be done in order to transport reversibly and isothermally an infinitesimal quantity of water, identical in composition to the soil water, from a pool at the elevation and the external gas pressure of the point under consideration, to the soil water at the point under consideration, divided by the volume of water transported.[1]
[edit] Pneumatic pressure
The amount of work that must be done in order to transport reversibly and isothermally an infinitesimal quantity of water, identical in composition to the soil water, from a pool at atmospheric pressure and at the elevation of the point under consideration, to a similar pool at an external gas pressure of the point under consideration, divided by the volume of water transported.[2]
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