Piezometers: Types, Functions, & How it works?
Piezometers are used to measure pore water pressure (Piezometric level) in the ground. The piezometer, also known as pore pressure meter, is used to measure pore water pressure in the soil, earth/rock fills, foundations and concrete structures. It provides significant quantitative data on the magnitude and distribution of pore pressure and its variations with time. It also helps in evaluating the pattern of seepage, zones of potential piping and the effectiveness of seepage control measures undertaken
Proper evaluation of pore pressure helps in monitoring the behaviour after construction and indicates potentially dangerous conditions that may adversely affect the stability of the structure, its foundation and appurtenant. It also provides basic data for design improvement that will promote safer and more economical design and construction.
Types of Piezometers
- Electric Piezometers
The next types of piezometers include electric piezometers that comprise of a deflecting diaphragm and a porous filter divided by a small reservoir of water. Vibrating wire or a strain gauge is used to calculate the deflections of the diaphragm. The calculated results are then converted to an equivalent pressure using a proper calibration. The next procedure is exactly similar to the open standpipe piezometers. The electric piezometer is inserted into a borehole while the annulus between the porous filter and the borehole is filled with cement/bentonite grout. Water from the ground pushes itself due to buoyant force into the reservoir and causes deflections in the diaphragm until the pressure inside the reservoir is the same as the pore water pressure (piezometric level) in the ground at the elevation of the porous filter. If an electric piezometer is installed above the current groundwater table, the pore pressure in the soil is negative and the water in the piezometer will be drawn out of the reservoir. If this happens, the piezometer will be filled with air, leading to its dysfunctioning.
- Hydraulic Piezometers
The third type of piezometers are the hydraulic piezometers that consist of a porous filter containing a reservoir of water, separated from a pressure gauge via resilient and water-filled tubes. These tubes circulate water through the system to remove air and ensure that the reservoir remains filled with water. The piezometer measures overall hydraulic pressure from which pore pressure can be calculated.
- Pneumatic Piezometers
The next type of piezometer is the pneumatic piezometer which is operated by gas pressure. It can be placed in a borehole, fills, or in a large diameter standpipe. The readings are then calculated with a pneumatic indicator.
- Vibrating Wire Piezometers
The Vibrating Wire Piezometers measure the pore water pressure in fully or partially saturated soil and rock. A vibrating wire piezometer basically consists of:
- A sensitive stainless steel diaphragm
- A magnetic, high tensile strength stretched wire, one end of which is anchored and the other end is fixed to a diaphragm.
- Ceramic low air filter (brass high air entry filters are also used depending on site requirements)
- Thermistor for temperature readings
- Glass to metal seal with four terminals for cable connection
- Stainless steel body with resistance to rusting or corrosion against several kinds of dissolved impurities found in water under field conditions. For saline water application, a special sensor with additional protection is provided
What is the pore water pressure/Piezometric Level?
The pore water pressure/Piezometric Level is the pressure experienced by water contained in pores of earth materials or concrete structures. In any instrumentation scheme for geotechnical or geo-structural study associated with large civil engineering structures like tall buildings, dams, underground tunnels etc., measurement of pore water pressure (also known as the piezometric level) plays an important part.
The study of pore pressure has the following main purposes:
- Effect of water in pores of soil or (see more)
