Multi-Point Borehole Extensometers


Stability and movement behavior of soil and rock masses can be determined by the use of borehole extensometers.


Add to Quote

Product Features

  • Accurate and reliable
  • Anchor lengths can be varied in the field. * for Rigid Rod Extensometers only.
  • Easily adapted to remote readout
  • Rugged, easy to install, and simple to operate.


Stability and movement behavior of soil and rock masses can be determined by the use of borehole extensometers. A typical rod extensometer consists of a reference head, usually installed at the collar of a drill hole, and one or more in-hole anchors, each of which is fixed in place at a known depth in the borehole. As the soil or rock deforms, the distances between adjacent in-hole anchors change, as do the distances between the individual in-hole anchors and the reference head. This allows an accurate determination of distribution, magnitude, rate and acceleration of deformation in the rock or soil mass intersected by the drill hole.

The number of anchors and anchor depths should be selected based on site geology, geometry of structures in the area, and other site-specific details. The use of two, or more, anchors at various depths allows the engineer to distinguish between potentially dangerous deep seated movements and more trivial surface spalling.

Sensor Range 50, 100, 150, 200 mm
Accuracy +/- 0.25% FSR
Resolution 0.025% FSR
Linearity 0.5% FSR
Operating Temperature -20°C to 80°C
Thermal Zero Shift <0.05% FSR/°C
Number of Anchors 1 to 6
Borehole Diameter Recommendation Minimum 4″ (101 mm)

Contact RST Instruments for available custom options.



1) Select Above Grade or Below Grade Installation
2) Select Manual or Combination Head
3) Select type and range of sensors
4) Select type and length of rods
5) Select type of anchors





ITEM Part #
Combination Heads MPBX
Mechanical Heads EXMPBXMA1 (1 point)

EXMPBXMA2 (2 points)

EXMPBXMA3 (3 points)

EXMPBXMA4 (4 points)

EXMPBXMA5 (5 points)

EXMPBXMA6 (6 points)


1/4 in. Standard, Stainless Steel Individual PVC Sheath EXRO2502 (0.25 m)
EXRO2505 (0.5 m)
EXRO2510 (1.0 m)
EXRO2515 (1.5 m)
EXRO2520 (2.0 m)
EXRO2530 (3.0 m)
EXRO2535 (3 ft.)
EXRO2550 (5 ft.)
EXRO2600 (10 ft.)


Groutable EXMP11000M (metric)
EXMP11000 (imperial)
Hydraulic Borros EXHY13000 (double acting)
Groutable with Spring Legs EXMP12000M (metric)
EXMP12000 (imperial)
Bladder Anchor EXIL14000 (customer specifies borehole diameter)

Borehole Extensometers are commonly used for:

  • Monitoring deformation around underground excavations.
  • Consolidation settlement in soils.
  • Strain in concrete structures.
  • Pile load tests.
  • Deformation of foundations in and under buildings.
  • Movement behind the face of excavated slopes.
  • Bottom heave in open cut excavations.
  • Subsidence over mines, tunnels, etc.
  • Monitoring of mine pillar deformation.
  • Roof and wall stability in mines and underground workings.

View illustrations on how Borehole Extensometers are used for:

Ordering Info Considerations

Rod assembly type and material.
Number of anchors, type and depths.
Reference head type -if electrical, specify sensor type, range and accuracy.
Accessories required.
Cable length.
Borehole diameter.
Environmental considerations.
Extension or compression expectations.
Drilling method, soil and/or rock types.
Orientation of borehole.
How will the extensometer head be connected to the ground at the borehole collar?


Accessories & Optional Equipment

Depth micrometer for Mechanical or Combination Heads. EXDM150DT
(metric, 0-150 mm range)
Hydraulic pump for hydraulic anchors. EXHYDPUMP
(up to 55 in³ oil capacity)
(up to 20 in³ oil capacity)
Grout and/or bleed tubes  


Contact RST for details.

Portable readouts
Terminal stations
Data loggers
Setting tools
Rod spacers


1-3 Point Extensometer Cable EL360008
4-6 Points Extensometer Cable EL38007P

File Name

Multi-Point Borehole Extensometers

Resource Type

Language Version Download
English EXB0029F

File Name

Vibrating Wire 2-3 Point Borehole Extensometer Installation Manual

Resource Type

Language Version Download
English EXM0109B

Speak with an Expert

I’m very happy with the quality of the instrumentation and technical support from RST, as always. They worked with us from the initial stages of the project to ensure that we were fully prepared and equipped to use the RSTAR network for the first time. They delivered everything within the tight project time frame to ensure that there were no delays on site, and the submersible tilt meters looked like new even after over twelve months of being submerged in Thames water!
-Richard Lipscombe, BEng (Hons), Director & Principle Consultant - RL Geotechnical Ltd