A geotechnical instrument called a piezometer is used to measure the ground’s pore water pressure, also known as the piezometric level. intended to monitor the pressure of pore water in rock, soil, foundations, and concrete constructions. Pore pressure gauges, also known as piezoelectric gauges, provide crucial quantitative information on the distribution and magnitude of pore pressure as well as how it changes over time. Evaluating seepage trends, possible pipe locations, and the success of put in place seepage control methods are also helpful.
It is regarded as one of the most crucial geotechnical monitoring instruments, and it makes for fascinating research. Well, in this reading, Let’s examine piezometers in more detail, including their kinds, Application, its functions, types, diagram, advantages and disadvantages & how it works.
Let’s Get Started!
What Is Piezometer?
Piezometer are the geotechnical sensors that are used to measure pore water pressure (piezometric level) in the ground. By measuring the height to which a fluid column rises against gravity, or groundwater pressure (mor accurately, a piezometric head) at a particular location, a piezometer may be used to quantify fluid pressure in a system. Unlike a pitot tube, which is aimed toward the fluid flow, a piezometer is intended to monitor static pressure. Though they need to be manually read, observation wells give information on the water level in the formation. It makes data collecting more convenient by having the ability to automatically read many kinds of electrical pressure transducers.
Piezometers provide crucial data for assessing site conditions, filling safety factors, slope stability prediction, and safety. They ensure stability, withstand pressure, assess drainage efficiency, and verify proper containment systems, ensuring safety and efficiency.
How Does a Piezometer Works?
The water pressure below the surface is measured using a piezometer. Through the use of a tensioned steel wire and a diaphragm, it transforms the water pressure into an electrical signal. The wire tension varies with variations in the diaphragm pressure. A high-strength magnetic tension wire with one fixed end and the other end connected to a fixed diaphragm that deflects in response to an increase in applied pressure is the fundamental construction of a vibrating wire piezometer.
The diaphragm deflects proportionately to variations in pressure, influencing the stretched wire’s tension. Thus, wire tension is directly impacted by variations in pore pressure. The wire is pulled by a coil magnet. Proportional to the tension of the wire, it resonates at the frequency “f”, which can be determined as follows:
f = {[σg/ρ] ^1/2}/ 2l Hz
Where:
- σ = tension of the wire
- g = gravitational constant
- ρ = density of wire
- l = length of wire
The coil’s magnet experiences an alternating current due to the wire’s resonance frequency. Pore pressure is immediately shown in engineering units by the Encardio-rite Model EDI-51V Readout Logger (Data Logger), which operates on the square of frequency.
The study of water’s effect on soil or rock pores can lead to reduced load bearing capacity, with higher pore water pressure causing total failure. Piezometers are used to determine groundwater levels and flow patterns in soil/rock embankments, concrete dams, and their foundations. There are several types of piezometers, including standpipe piezometers, vibrating wire piezometers, pneumatic piezometers, titanium piezometers, and Casagrande or open standpipe piezometers.
Standpipe piezometers are the most fundamental type, consisting of a riser tube and a filter tip connected to it. Water enters the riser tube via the filter tip, and measurements are made at the indication of water level. Vibrating wire piezometers are popular and can be placed in boreholes, embedded infills, or hung on a standpipe. Pneumatic piezometers activate when gas pressure is applied, and can be suspended on a large diameter standpipe, placed in a borehole, or implanted in filler.
Titanium piezometers are used in industrial data recorders for testing drop-downs. Open standpipe piezometers, also known as Casagrande’s, are basic tools for determining the piezometric level in the ground. They are made of plastic, have a small diameter, and have a porous bottom piece. Water is forced into the standpipe by groundwater pressure until the water level at the height of the porous filter equals the ground’s piezometric level (pore water pressure).
Piezometers are simple and reliable tools used to measure static pressure and vacuum pressure in fluids. They are used for pore water pressure/groundwater level, soil and rock performance calculations, and self-de-airing standpipes. However, they cannot determine high pressure or vacuum pressure in liquids, are not ideal for measuring vacuum pressure, and cannot be used to measure gas pressure. Piezometers are simple, cheap, and reliable when installed well. They can also estimate permeability if the standpipe is larger than 12mm.
