Pore water pressure

The vertical pore water pressure distribution in aquifers can generally be assumed to be close to hydrostatic.

A correct representation of stress in the soil is necessary for accurate field calculations in a variety of engineering trades.

The United States Bureau of Reclamation has a standard for monitoring water pressure in a rock mass with piezometers.

It sites ASTM D4750, "Standard Test Method for Determining Subsurface Liquid Levels in a Borehole or Monitoring Well (Observation Well)".

[8] Increased water infiltration, such as that caused by heavy rainfall, brings about a reduction in matric suction, following the relationship described by the soil water characteristic curve (SWCC), resulting in a reduction of the soil's shear strength, and reduced slope stability.

[9] Capillary effects in soil are more complex than in free water due to the randomly connected void space and particle interference through which to flow; regardless, the height of this zone of capillary rise, where negative pore water pressure is generally peaks, can be closely approximated by a simple equation.

[10] An ISO standard, "Soil quality — Determination of pore water pressure — Tensiometer method", ISO 11276:1995, "describes methods for the determination of pore water pressure (point measurements) in unsaturated and saturated soil using tensiometers.

A vibrating wire piezometer. The vibrating wire converts the fluid pressures into equivalent frequency signals that are then recorded.
Electronic tensiometer probe: (1) porous cup; (2) water-filled tube; (3) sensor-head; (4) pressure sensor