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!
Contents
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.
Piezometer Application
Piezometers give crucial data for the following purposes by measuring groundwater level and pore water pressure:
- Recognize the fundamental site conditions.
- Calculating the filling safety factor Slope stability prediction.
- Made to withstand lateral ground pressure.
- Assessing the drainage plan’s efficacy.
- Verify that the containment systems are working properly.
Diagram
Functions of Piezometer
- To study the effect of water in the pores of soil or rock is to reduce load bearing capacity of soil or rock. The effect is more pronounced with higher pore water pressure leading eventually in some cases to total failure of load bearing capacity of the soil.
- Determination of groundwater level and flow patterns
- Determines water flow patterns in soil/rock embankments, concrete dams and their foundations.
- To delineate the phreatic line.
Types Of Piezometer
1. Standpipe Piezometers.
The most fundamental kind of piezometer is the standpipe model. It is made up of a riser tube that reaches to the surface and a filter tip connected to it. Water enters the riser tube via the filter tip. Measurements are made at the indication of water level.
2. Vibrating wire piezometer.
The most popular kind of piezometer is the vibrating wire kind. It may be put in a borehole, embedded infill, or hung on a standpipe, making it suitable for most purposes. A data logger or portable readout is used to collect readings.
3. Pneumatic Piezometers.
Gas pressure is what activates a pneumatic piezometer. It may be suspended on a large diameter standpipe, placed in a borehole, or implanted in filler. An indicator that is pneumatic is used to take readings.
4. Titanium piezometer.
Industrial data recorders may work with the 4–20 mA titanium piezoelectric meter. Usually used to testing drop-downs.
5. Casagrande or Open Standpipe Piezometers
An Open Standpipe Piezometer, also known as a Casagrande, is among the most basic tools for determining the piezometric level in the ground. The pipe is made of plastic, has a tiny diameter (up to 20 mm), and a porous bottom piece.
The porous piece of this pipe is placed at the bottom of the borehole, where the piezometric level is to be measured, and the pipe is put inside. The remainder of the borehole is filled with cement mortar, and the annulus between the porous filter and the borehole is filled with sand that has been sealed with bentonite on both sides.
Water is forced into the standpipe by groundwater pressure until the water level (h) at the height of the porous filter equals the ground’s piezometric level (pore water pressure). The piezometer water level is utilized and tracked in this manner.
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.
Advantages Of Piezometer
- Simple and reliable
- It is used to measure the static pressure of fluids in vessels.
- One of the main applications of piezoelectric transducers is the measurement of pore water pressure/groundwater level.
- It helps to calculate soil and rock performance.
- They are simple, cheap and if they are installed well they are generally reliable.
- If the standpipe is larger than 12mm, open standpipes are self de-airing
- They can be used to estimate permeability.
Disadvantages Of Piezometer
- As such, it is unable to determine a liquid’s high pressure or vacuum pressure.
- Not ideal for measuring vacuum pressure.
- Not useful for measuring high levels of pressure in light liquids.
- Can’t be used to measure gas pressure.
- The vacuum pressure cannot be measured by it.