Extensometer: Types, How It Works, Applications | Encardio-Rite
August 7, 2019
Geotechnical instrumentation and monitoring is a vast field that includes several monitoring instruments such as piezometers, tiltmeters, strain gauges, beam sensors, extensometers etc.
Extensometers or extension-meters are extensively used to measure the change in the length of an object. They are designed for strain measurements or to carry out tensile tests.
Since extensometers are one of the most significant monitoring instruments, let us give you a better insight into its working principle, construction, specifications, and application areas.
What Is An Extensometer?
An extensometer is a high precision instrument specially designed for geologists or civil engineers to measure the elongation of a material under stress. This instrument is perfect for tensile tests.
It can also determine yield strength, tensile strength, yield point elongation, strain-hardening exponent, and strain ratio.
Besides this, extension-meters have a huge scope of work in the geotechnical field. They are available in various types and sizes depending upon the application area.
How does an extensometer work?
Usually, the extensometers are classified as contact, non-contact, laser, and video extensometers.
However, the working principle of extension-meters depends on its type as well as the application area. Encardio-Rite deals with a wide range of extensometers, including magnetic, electrical, mechanical, and soil extensometers. All of these extension-meters have different working principle.
Magnetic Extensometer
The magnetic extensometer system is designed to measure settlement or heave of the soft ground under the influence of loading or unloading due to the construction of embankments, fills, buildings, and structures.
Lateral movement at any level within a soil mass may be assessed by monitoring the location of magnetic targets positioned over a near-horizontal access tube. The lateral ground movement may be in abutments, foundations or embankments, and a consolidation-induced settlement in embankments and foundations.
Electrical Extensometer
The electrical borehole extensometer incorporates a vibrating wire transducer for measurement of displacement. A groutable reinforced bar anchor (1) is attached to fibreglass (2.a) or AISI 410 stainless steel (2.b) connecting rods of appropriate length, as specified in the design.
Fibreglass connecting rods are supplied from the factory in single lengths. The connecting rods are enclosed inside heavy-duty protective tubing to allow for free movement. The displacement sensor is coupled to the connecting rod using link plate and lock nut.
Mechanical Extensometer
The borehole extensometer measures the extension (displacement) which takes place with time in a borehole or several boring holes in a rock mass. It essentially consists of one or more anchors and a reference plate. The anchor or anchors are set in the same borehole or different boreholes drilled adjacent to the first borehole.
They help to accurately measure the distance between the various anchors with respect to the reference plate and monitor their relative displacement with time. It is usually assumed that the deepest anchor is in the stable ground and so any change in the anchor spacing gives information about the settlement of foundation taking place.
Soil Extensometer
The soil extensometer uses a vibrating wire sensor for monitoring displacement. The system consists of a sensor assembly with flanges that are mounted with adaptors, adjustment unit, sockets and extension rods between two anchors to monitor the horizontal movement of surrounding soil.
The system is enclosed in telescopic PVC tubing with proper ‘O’ ring seals to eliminate friction between the rods and surrounding soil and to prevent any ingress of water.
The extensometer system is supplied with different gauge lengths (gauge length is the distance between two anchors).
Several extensometer units can be connected in series to measure incremental displacements over large distances. Movement of relative position between two anchor channels at the ends of the soil extensometer is representative of the mass movement.
The relative movement between the anchors causes a change in the output of the vibrating wire sensor. This output can be measured by Encardio-rite model EDI-51V portable read-out unit/datalogger or monitored by a remote model EDAS-10 data acquisition system.
The initial reading is taken as the datum. The difference between subsequent readings and initial reading gives the magnitude of the movement.
Uses of extensometer in the geotechnical field
- To determine how the roof or wall of mine, under..(Read More)
