Using a Piezometer to Measure the Pressure of Groundwater

A vibrating wire piezometer is a fluid pressure measurement instrument using a proven technique of converting fluid pressure on a sensitive diaphragm into a frequency signal. Frequency signals are ideal in Civil Engineering applications where work is conducted in demanding environments because they can travel long distances without degrading. Moreover, they can resist external electrical noise and tolerate wet wiring conditions. A piezometer is typically used in applications like finding the fluid pressure in pump and hydro-fracture tests and measuring the pore pressure in rocks and soils.

Vibrating Wire Piezometers operate as follow:

• When the tension wire is plucked by an electronic pulse to the measurement coil which surrounds the wire it vibrates at a resonant frequency, thus activating the gauge.

• A magnetic coil surrounds the wire, when the wire is plucked and vibrates an electric signal is created which can be used to find the vibration’s resultant resonant frequency.

• On a VW piezometer, the wire is tensioned between an anchor point and a diaphragm. The changes in the distance between the diaphragm and the anchor are related to the pressure differentials. They can be converted into a kPa reading.

• Temperature information can be utilised from an internal temperature sensor if regular logging is required. This way, swift changes in temperature can be determined as pressure readings have the potential to be exaggerated.

Measuring the pore pressure of groundwater can help you understand the behaviour of the ground. This data can be most especially crucial before, during, and after a construction project. A conventional piezometer is an open standpipe made of plastic pipe that is 19mm in diameter, with a porous area at the bottom. It is installed in a borehole with the porous section situated at the depth where you need to measure pore water pressure. Sand is used to fill an annulus between the borehole and the filter, then sealed with bentonite before the remaining area of the borehole is filled with grout, which is typically made of cement and bentonite. Results are normally collected by measuring the height of water, but VW piezometers can directly record pressure allowing for automatic data collection

Certain features make high-end piezometers reliable when measuring pressure of groundwater in the most demanding conditions. A vibrating wire piezometer for instance, has a rugged construction so it can withstand the harshest environments and guarantee long-term, reliable performance. The device is insensitive to the length of a cable, so it does not matter if you use a long cable. Be sure to purchase a piezometer from a reputable provider, especially if you are buying a non-drive-in model. That way, you can have it customised as per your unique specifications.

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