Piezometers

A piezometer is a device used to measure fluid pressure within a system. In geotechnical engineering and hydrogeology, the term most often refers to devices that measure pore water pressure in soils or rock, rather than the pressure of a gas or liquid in a closed container.

Pore water pressure data are used to determine hydraulic head, assess soil strength under load (through effective stress), monitor groundwater flow, and evaluate drainage or dewatering systems. Piezometers provide a direct measurement of the pressure within the pore fluid, which, together with elevation data, informs interpretations of hydraulic conditions.

Common types include open-tube (standpipe) piezometers, which show the height of the water column corresponding to hydraulic head, and vibrating-wire or other sensor-based piezometers that house a pressure sensor in a borehole and transmit readings electronically. Piezometer tubes can be installed in boreholes with a perforated section or used as simple standpipes in the ground. Observation wells provide access to deeper formations.

Installation involves placing the sensing element so that the fluid pressure at a chosen depth is transmitted to the sensor, often requiring grout or sealing to isolate the measurement zone. Readings can be affected by temperature, barometric pressure, and seepage, so corrections or venting may be needed.

In practice, piezometer readings are interpreted as part of hydraulic head h = z + p/γ_w, where z is elevation and p is pore water pressure. Units are typically meters of water, or kilopascals. Modern systems use data loggers or telemetry for continuous monitoring. Limitations include potential soil disturbance during installation, calibration requirements, and the need for regular maintenance to prevent clogging or drift.