Piezometer or pore pressure meter is one of the most extensively used geotechnical instruments. But before we move forward, let’s see what Piezometers measure?
A piezometer is 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 piezometer types. Let’s discuss each one of them in detail along with their features and applications.
Before going in-depth of each model, ask yourself this simple question.
What Is the Need to Study Pore Pressure?
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. More the content of water in the pores, less will be 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.
Piezometer Types
The piezometers are available in different shapes and sizes, depending upon the application. The most common types of piezometer 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, also known as the casagrande type piezometer. 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/Casagrande 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 same diameter plastic standpipes extending to the surface.
The borehole is filled with pea gravel while sealing its top with 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 locking arrangement is available for mounting at top of the standpipe. The locking arrangement has a universal key and a dust protection ...[Continue Reading]
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