Extensometer Types, How It Works, Applications by Encardio-rite

1. EXTENSOMETERS Types, How it Works & Applications

2. 1 INTRODUCTION 2 WHAT IS AN EXTENSOMETER? TABLE OF CONTENT 3 HOW DOES AN EXTENSOMETER WORK? 4 USES OF EXTENSOMETER IN THE GEOTECHNICAL FIELD 5 WHAT ARE THE TYPES OF EXTENSOMETERS?

3. 1 INTRODUCTION 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.

4. 2 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. It can also determine yield strength, tensile strength, yield point elongation, strain-hardening exponent, and strain ratio.

5. 3 HOW DOES AN EXTENSOMETER WORK? 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. Magnetic Extensometer The magnetic extensometer system is designed to measure settlement or heave and lateral or horizontal ground movement of the soft ground under the influence of loading or unloading due to the construction of embankments, fills, buildings, and structures.

6. 3 HOW DOES AN EXTENSOMETER WORK? 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. 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.

7. 3 HOW DOES AN EXTENSOMETER WORK?

8. 3 HOW DOES AN EXTENSOMETER WORK? 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. The anchor or anchors are set in the same borehole or different boreholes drilled ad- jacent to the first borehole. They help to accurately measure the distance between the various anchors with re- spect to the reference plate and monitor their relative displacement with time.

9. 3 HOW DOES AN EXTENSOMETER WORK? 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 adap- tors, adjustment unit, sockets and extension rods between two anchors to monitor the horizontal movement of surrounding soil. Movement of relative position between two anchor channels at the ends of the soil extensometer is representative of the mass movement.

10. 4 USES OF EXTENSOMETER IN THE GEOTECHNICAL FIELD • To determine how the roof or wall of mine, underground cavity or tunnel behaves during excavation operation & to study the effectiveness of the support system. • To predict potential roof or wall fall before it occurs. Roof or wall fall in an under ground cavity is almost invariably preceded by measurable sag as the strata open up, and the movement usually occurs at an increasing rate as fall conditions are ap proached. Unsuspected roof and wall fall conditions are approached that may result in serious accidents. • To measure and monitor the movement in a slope or foundation due to the excavation of underground cavities or due to the construction of a heavy structure like concrete, rock fill, masonry or earth dam over the foundation. • To measure horizontal and vertical movement in foundations and embankments. • To measure the movement of natural and cut slopes, quarry and mining excavations.

11. 4 USES OF EXTENSOMETER IN THE GEOTECHNICAL FIELD • To calculate the displacement of retaining walls, piers & abutments. • To measure the displacement around tunnels & underground cavities. • They are used for highly accurate measurements of relative deformations of multiple segments along the entire pile length.

12. 5 WHAT ARE THE TYPES OF EXTENSOMETERS? Model EDS-63U-D Mechanical Borehole Extensometer System The Encardio-Rite Model EDS-63U-D mechanical borehole extensometer is ideally suited for upward, downward or inclined boreholes. Together with anchor bolt load cell and tape extensometer, it is essential equipment for investigation and monitoring of foundations, slopes & embankments and for studying the behaviour of rock around underground cavities, tunnels and mines.

13. 5 WHAT ARE THE TYPES OF EXTENSOMETERS? The measurement with Model EDS-63U-D borehole extensometer is economical, very reliable and is preferred at locations where access to the mouth of the borehole is easily available The Model EDS-63U-D borehole extensometer with up to three positions can be in- stalled in a 3” φ NX (76 mm φ) borehole; with up to six positions, it can be installed in a 100 mm φ borehole. Groutable anchor is ideally suited when it is not possible to install expandable an- chors at locations where the rock formation is soft.

14. 5 WHAT ARE THE TYPES OF EXTENSOMETERS? Model EDS-64U-D Mechanical Borehole Extensometer System The Encardio-Rite Model EDS-64U-D single position mechanical borehole extensom- eter is suitable for 50 mm upward, downward or inclined boreholes. It is a precision mechanical instrument designed to measure the deformation of rock mass and adjacent or surrounding soil.

15. 5 WHAT ARE THE TYPES OF EXTENSOMETERS? Model EDS-70V/EDS-70P Electrical Borehole Extensometer System The Encardio-rite Model EDS-70V multi-point borehole extensometer is a precision instrument designed to help civil engineers and geologists in the measurement of deformation of rock mass & adjacent or surrounding soil. The borehole extensometer is an important instrument especially in the investigation of underground cavities & landslides.

16. 5 WHAT ARE THE TYPES OF EXTENSOMETERS? The Model EDS-70V borehole extensometer incorporates a vibrating wire transducer for measurement of displacement. EDS-70V can be ordered from the factory for monitoring settlement at up to six depths. It is suitable for a 3” Ф (~76 mm) borehole for up to 1~3 points & 4” Ф (~102 mm) borehole for 4~6 points. Model EDS-70M version of this borehole extensometer is available for taking the reading with a mechanical dial gauge and is supplied without the vibrating wire sen- sors. Model EDE-VXX vibrating wire linear displacement transducer incorporates a vibrat- ing wire sensor having a stroke of 50 mm (EDE-V05), 100 mm (EDE-V10) or 150 mm (EDE-V15).

17. 5 WHAT ARE THE TYPES OF EXTENSOMETERS? Model EDS-71V/EDS-71P Electrical Borehole Extensometer System The Encardio-Rite Model EDS-71V electrical borehole extensometer is a precision in- strument designed to help civil engineers and geologists in the measurement of de- formation of rock mass and adjacent or surrounding soil.

18. 5 WHAT ARE THE TYPES OF EXTENSOMETERS? Model EDS-91 Magnetic Extensometer System The Encardio-rite Model EDS-91V/H magnetic extensometer is used to measure ver- tical settlement or lateral movement depending on the application. Settlement or heave at various levels within a soil mass may be assessed by moni- toring location of magnetic targets which have been positioned over a near-vertical access tube.

19. 5 WHAT ARE THE TYPES OF EXTENSOMETERS? For monitoring settlement only, regular access tubing is used. For monitoring lateral displacement along with the settlement, inclinometer casing with telescopic coupling is used. For vertical installation in an earth fill, 3 m long tubes are connected, one by one, with telescopic couplings to keep pace with the fill operation. For horizontal installations, similar telescopic access tubes are laid at the base of the trench, with magnet plates embedded in the trench floor. The probe, 22 mm Φ x 150 mm long has a reed switch encapsulated inside it in sili- con rubber for protection against shock, corrosion and ingress of water. The moisture-resistant electronics and standard 9 V PP-3 size battery are housed in a hub on the cable reel & can be easily removed to replace the battery or check the electronics without disassembling the entire cable reel.

20. 5 WHAT ARE THE TYPES OF EXTENSOMETERS? Model EDS-92 Soil Extensometer The Encardio-rite model EDS-92 extensometer is used for monitoring displacement between two surfaces that may shift with respect to each other with time. The soil extensometer finds major application in the measurement of lateral strains and settlement in or beneath earth/rock fill embankments.

21. 5 WHAT ARE THE TYPES OF EXTENSOMETERS? The displacement of retaining walls, bridge piers and abutments can also be moni- tored by the soil extensometer. It also measures displacement across construction joints in concrete, and across joints/faults in the rock. The extensometers are usually installed in approximately 500 mm wide x 600 mm deep trenches.

22. 5 WHAT ARE THE TYPES OF EXTENSOMETERS? Model EMA-11 Measuring Anchor The Encardio-Rite Model EMA-11 measuring anchor (rock bolt extensometer), is a combination of rock bolt and an extensometer. EMA-11 Measuring anchor is used to determine the load exerted on rock bolts. The principal function of measuring anchor is to determine the depth where force is exerted on the bolt due to loosening effects of rock.

23. 5 WHAT ARE THE TYPES OF EXTENSOMETERS? Model EMA-11 measuring anchor has a breaking force of up to 250 kN and the length offered ranges from 3 m to 6 m. The change in length due to compression or extension between individual measur- ing bars are taken by measuring the depth of the near end of the respective measur- ing bars from a reference plate provided at the mouth of the borehole. A digital calliper/micrometre depth gage with a resolution of 0.01 mm is used to take the readings.

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