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1. INTRODUCTION
The Model 1900 Magnetic Extensometer is designed to measure movement between magnetic
targets anchored in the ground. It is normally installed in a borehole or directly in fill as it is
placed. The primary use of the Magnetic Extensometer is the measurement of vertical
compression in embankments, foundations, and fills and the movement of settlements in soft
ground due to the placement of fills and embankments. It may also be used to measure heave.
1.1 Theory of Operation
Figure 1 shows the basic arrangement of the Magnetic Extensometer.
Top Cap
Telescoping Coupling
with O -ring Seals
Flush Coupled
Access Tube
(or Inclinometer Casing)
Datum Magnets
Borehole Installation
Manhole
with Cover
End Cap
(m echanically released)
Spider Magnet
Spider Magnet
Soft Bentonite Grout
Protective Cover
Top Cap
Plate Magnet
Telescoping Coupling
with O -ring Seals
Fill
Flush Coupled
Access Tube
(or Inclinometer Casing)
Datum Magnets
Installation in Fill
End Cap
Cable R eel
with Audible
Nylon Coated Steel Tape
Reed Switch Probe
(push-in type)
Figure 1 - Typical Magnetic Extensometer Installations
Summary of Contents for 1900
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