A piezometer or pore pressure meter is one of the extensively used geotechnical instruments. The piezometers are primarily used to measure pore pressure in concrete structures, boreholes, rock fills, soil, etc. However, different types of piezometers find their application in the geotechnical or geo-structural study associated with large civil engineering constructions like tall buildings, dams, underground tunnels, etc.
Encardio Rite mainly deals with four different models of Vibrating Wire Piezometers. Let us discuss each one of them in detail along with their features and applications.
Before going in-depth about each model, can you answer this simple question?
What Is the Need to Study Pore Pressure?
Well, the pore pressure study is necessary because of the following reasons:
The water in the pores of soil or rock diminishes its capability to hold the structure. The more the content of water in the pores less the load-bearing capacity of the soil/rock. And, building a structure over such soil leads to destruction and failures.
Groundwater is one of the most fundamental resources and, piezometers are used to determine its level as well as the flow.
The water flow pattern measurement in earth/rockfill & concrete dams and their foundations is necessary to delineate the phreatic line.
Types of Piezometer
The piezometers are available in different shapes and sizes, depending upon the application. The most common piezometer types include:
- Standpipe Piezometer
- Vibrating Wire Piezometers
- Pneumatic Piezometers
What is a standpipe piezometer?
The most basic piezometers that are used to measure pore pressure are the standpipe piezometers. It consists of a filter tip and a riser pipe that is attached to each other and extended to the surface. The water seeping out from the soil or rocks flows through the filter and up to the riser pipe. The water level readings are then measured by a water level indicator.
The standpipe consists of a series of PVC standpipes, 50 mm o.d., 44.5 i.d., and 3 m length with an inbuilt socket for jointing. The intake point of the standpipe consists of a PVC slotted pipe, 1 m long, 50 mm o.d., covered with geotextile. The bottom end of the slotted pipe is plugged with a suitable PVC cap.
Standpipe Piezometer: Operating Principle
The standpipe is set in a borehole, which is drilled into the soil/foundation to a pre-determined depth to intercept groundwater. The slotted pipe is connected by a socket to the same-diameter plastic standpipes extending to the surface.
The borehole is filled with pea gravel while sealing its top with a cement bentonite plug. Groundwater seeps into the standpipe through the slotted end and attains a level equal to groundwater. This level is determined by an electrical-sounding device model EPP10/6 lowered from the surface.
A plate-hinged cover with a locking arrangement is available for mounting at the top of the standpipe. The locking arrangement has a universal key and a dust protection cap.
Figure 1: Typical assembly and installation layout of the EPP-10SP standpipe.
Encardio Rite Model Standpipe Piezometer Specifications
| EPP-10 |
| Casagrande tip | 40 mm o.d., 27 mm i.d., 20, 40, 60 cm long |
| Standpipe | 25 mm o.d., 3 m long each |
| EPP-10SP |
| Porous tip | 50 mm o.d., slotted pipe -1 m or 3 m |
| Standpipe | 50 mm o.d., 3 m long each |
Vibrating Wire Piezometers
Vibrating wire piezometers are used to measure pore pressure in boreholes, rock fills, or a standpipe. The readings of a vibrating wire piezometer are captured through a data logger. Encardio Rite mainly deals with the following models of Vibrating Wire Piezometers:
- Model EPP-30V Vibrating Wire Piezometer
- Model EPP-40V Slim Size Piezometer
- Model EPP-50V Push-in type Vibrating Wire Piezometer
- Model EPU-20V Vibrating Wire Uplift Water System
- Model EPP-60V Low-Pressure Piezometer
Pneumatic Piezometers
The piezometers that are operated by gas pressure are known as pneumatic piezometers. Such piezometers can be installed in boreholes, large-diameter standpipes, and fills. The readings are captured through the pneumatic indicator.
Read more: Piezometers: Types, Functions, & How it Works?
Encardio Rite Piezometer Types
Model EPU-20V Vibrating Wire Uplift Water System
The Model EPU-20V, VW uplift pressure meter is used for monitoring uplift pressure of water in the foundation of dams and concrete structures, the stability of foundations of embankments in dams, tunnels, and other underground works.
It provides significant quantitative data on the magnitude and distribution of uplift pressure of water and its variation with time. It also provides the pattern of seepage, zones of potential piping, and the effectiveness of seepage control measures undertaken.
The uplift pressure measuring device consists of a perforated/non-perforated pipe of 50 mm diameter of adequate strength. The pipe is inserted in a drilled hole in the foundation from the instrumentation gallery to the required depth. The other end of the pipe in the gallery is connected with the uplift pressure meter or a Bourdon pressure gage.
Vibrating Wire Uplift Water System Specifications
| Range (MPa) | 0.2, 0.35, 0.5, 1.0, specify |
| Accuracy | ± 0.25 % fs standard | ± 0.1 % fs optional |
| Non-linearity | ± 0.5 % fs |
| Over range limit | 150 % fs of range |
| Temperature limit | -20° to 80° C |
| Thermistor | YSI 44005 or equivalent |
| Dimension (Φ x L) | 42 x 210 mm |
Model EPP-30V Vibrating Wire Piezometer
The Model EPP-30V, vibrating wire piezometer consists of a vibrating wire and coil magnet assembly enclosed in a stainless steel body electron beam welded to the diaphragm. The welding creates a vacuum of around 1/1000 Torr inside the sensor to protect it against water and other corrosive materials present in it.
The stainless steel body of the piezometer makes sure that it is unaffected by common chemical corrosion. There’s a ceramic flat filter with a low air entry value along with a grain size of 40-60 microns. The water that seeps through the internal pores or seams in mass concrete structures, rock formations of dam foundations, foundation soil of structures, reclaimed land soil, etc. penetrates through the ceramic filter thereby, exerting pressure on the diaphragm.
A nut holds the filter in position despite the pressure exertion. A bent nose plier is used to remove and assemble the locking nut again to fill up the cavity behind the filter with de-aired water before the installation process.
The porosity and air entry values of the filters depend upon the area of application. The leads from the coil magnet are then connected to the glass to the metal seal which is an electron beam welded to the piezometer. The pins marked as red and black are attached to the coil magnet while the other two pins are connected to a thermistor. A cable joint housing and cable gland are provided for the connection.
Vibrating Wire Piezometer Specifications
| Range (MPa) | 0.2, 0.35, 0.5, 0.7, 1.0, 1.5, 2.0, 3.5, 5.0, 10.0, specify |
| Accuracy | ± 0.25 % fs standard | ± 0.1 % fs optional |
| Non-linearity | ± 0.5 % fs |
| Over range limit | 150 % fs of range |
| Temperature limit | -20° to 80° C |
| Thermistor | YSI 44005 or equivalent |
| Dimension (Φ x L) | 42 x 185 mm |
Model EPP-40V Slim Size Piezometer
Model EPP-40V, slim size piezometer is used to measure the pore pressure in small diameter boreholes. The sensor is electron beam welded with a vacuum of around 1/1000 Torr inside it similar to EPP-3-V. It contains a low air entry value ceramic flat filter with a grain size of 40-60 microns. The cable connection through the glass to metal seal is done exactly like the Model EPP-30V. However, if specifically requested, the piezometers are supplied with the requisite length of cable attached.
Slim Size Piezometer Specifications
| Range (MPa) | 0.35, 0.5, 0.7, 1.0, 2.0 |
| Accuracy | ± 0.2 % fs standard | ± 0.1 % fs optional |
| Non linearity | ± 0.5 % fs |
| Over range limit | 150 % fs of range |
| Temperature limit | -20° to 80° C |
| Thermistor | YSI 44005 or equivalent |
| Dimension (Φ x L) | 19 x 155 mm |
Model EPP-50V Vibrating Wire Push-In Piezometer
Long-term stability is ensured in the Model EPP-50V, VW push-in piezometer by:
- Pressure and thermal cycling
- The unique method of wire clamping
- Generating a vacuum of around 1/1000 Torr inside the sensor by electron beam welding.
This results in the effect of oxidation, moisture, environmental conditions, and any ingress of water being eliminated.
The vibrating wire pressure-sensing capsule is sealed under a high vacuum. The capsule and coil magnet assembly is housed in a stainless steel body. The model EPP-50V vibrating wire push-in piezometer has a pointed cone at one end and drill rod threads (EW drill or M28) at the other end.
When threaded into a drill rod, the piezometer can be pushed into soft soil directly. The cable attached to the piezometer is passed through the drill rod. The piezometer must be monitored to ensure that the pressure created during installation does not exceed the maximum rated pressure.
EPP-50V/1 Stainless steel sensor
The vibrating wire and coil magnet assembly is enclosed in a corrosion-resistant stainless steel body which is electron beam welded to the diaphragm.
EPP-50V/2 Metallic filter
A low air entry value stainless steel filter of 40-micron porosity is provided. High-air entry filters are also available as an option. The filter can be taken out for saturation. A locking nut holds the filter in position through a suitable ‘O’ ring.
Vibrating Wire Push-In Piezometer Specifications
| Range (MPa) | 0.35, 0.5, 0.7, 1.0, 2.0 |
| Accuracy | ± 0.2 % fs standard | ± 0.1 % fs optional |
| Non linearity | ± 0.5 % fs |
| Over range limit | 150 % of range |
| Temperature limit | -20° to 80°C |
| Thermistor | YSI 44005 or equivalent |
| Dimension (Φ x L) | 35 x 166 mm |
Model EPP-60V Low-Pressure Piezometer
The Model EPP-60V, low-pressure piezometers is designed to measure low water pressure. The basic pressure sensor is conveniently designed to measure water level and pressure in boreholes. It provides significant quantitative data on groundwater level, groundwater pressure, and its variation with time.
Proper evaluation of water level helps in monitoring the behaviour after construction and indicates potentially dangerous conditions that may adversely affect the stability of the structure and its foundation. It also provides basic data for design improvement that will promote safer and more economical design and construction.
Low-Pressure Piezometer Specifications
| Electron Beam Welded |
| Range (MPa) | 0.10, 0.20 |
| Accuracy | ± 0.25 % fs standard | ± 0.1 % fs optional |
| Non linearity | ± 0.5 % fs |
| Over range limit | 150 % fs of range |
| Temperature limit | -20° to 80°C |
| Thermistor | YSI 44005 or equivalent |
| Dimension (Φ x L) | 30 x 160 mm |
| Vented Tube Cable |
| Range (MPa) | 0.035, 0.07 |
| Accuracy | ± 0.25 % fs standard | ± 0.1 % fs optional |
| Non linearity | ± 0.5 % fs |
| Over range limit | 150 % of range |
| Temperature limit | -20° to 80°C |
| Thermistor | YSI 44005 or equivalent |
| Dimension (Φ x L) | 30 x 160 mm |
| Cable | CS-1102 vented 1 m long; specify |
This was all about the piezometer types and the various Models of Encardio Rite pore pressure meters. If you have a query or suggestions to make, feel free to drop them in the comments section below.