Piezometer:
- Piezometer is a instrument which measures the pore water pressure or effective stress in a soil medium.
- It plays an important role in dam safety instrumentation.
- One can use it before construction of dam, during construction of dam and after construction of dam.
- Piezometers can be installed within structure of dam.
- It can also be used at the upstream or downstream of the structure.
Purpose of Piezometer:
Purpose of such instrument are as follows:
- For monitoring dam performance,
- Rate of construction,
- For slope stability assessment and ground improvements.
Types of Piezometers:
There are mainly two types of piezometers:
- Vibrating wire piezometer
- Pneumatic piezometer
1.Vibrating wire piezometer:
- One can use such type of piezometers to determine pore water pressure.
- It consist of porous stone connected to sealed metal chamber with diaphragm adjacent to the stone.
- One connects the chamber to an electronic readout device.
- Modern device readout calibration automatically.
Advantages:
Following are the various advantages of vibrating wire piezometers:
- It provides automatic data collection.
- It also provides remote data collection.
- Also provides good response time.
- It is moderately simple transducer.
- It is simple o monitor.
- Has very short lag time.
- Lastly, it has no freezing problems.
Disadvantages:
Following are the various disadvantages of vibrating wire piezometers:
- Firstly, it requires power.
- It gives incorrect readings in unsaturated conditions.
- Require lighting protection.
- It is expensive transducer and readout.
- It is sensitive to temperature and barometric pressure changes.
- lastly, there is risk of zero drift, but some models are available with in-situ calibration check.
2.Pneumatic Piezometer:
- This type of piezometers consists of a porous filter connected to two tubes having flexible diaphragm in-between.
- It holds the diaphragm closed with the help of external water pressure.
- The end of one of the tube is attached water pressure.
- The end of one of the tubes is attached to a dry air supply and a pressure gauge.
- One can use it to determine the ground water pressure and pore water pressure in saturated soil.
Advantages:
Following are the various advantages of pneumatic piezometers:
- Firstly, it is moderately simple transducer.
- Secondly, Frequency output signal permits transmission over the long distances.
- Thirdly, it is easily automated.
- Fourthly, moderately expensive.
- Fifthly, it is more reliable and keep fairly long experience record.
- Sixthly, it makes remote reading possible.
- Lastly, One can calibrate it at any time.
Disadvantages:
Following are the various disadvantages of pneumatic piezometers:
- Firstly, it has moderately complex monitoring and maintenance.
- Secondly, it is difficult to be automate for long distances.
- Thirdly, Condensation can cause inaccurate readings if one does not controls it properly.
- Fourthly, it require dry air and readout device.
- Fifthly, it is sensitive to barometric pressure.
- Lastly, it has moderately expensive readout.
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