sensors

VW Borehole Extensometer

Multi-point extensometer for measuring deformation at various depths within rock or soil masses.

Range
50, 100, 150 mm
Accuracy
±0.1% F.S.
Resolution
0.025% F.S.

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Overview

Multi-point extensometer for measuring deformation at various depths within rock or soil masses.

The Geolook Vibrating Wire Borehole Extensometer (MPBX) is a precision instrument designed to monitor deformation and settlement at multiple depths within a single borehole. It is the industry standard for measuring the stability of tunnels, underground powerhouses, open-pit mines, and deep excavations. The system consists of a reference head assembly installed at the borehole collar and multiple downhole anchors located at critical depths. Connecting rods link the anchors to the head, where vibrating wire transducers measure the relative displacement. This multi-point configuration allows engineers to create a complete profile of ground movement, distinguishing between shallow surface settlement and deep-seated instability.

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Benefits & Features

  • Multi-Point Monitoring (up to 6 anchors per hole)
  • High-precision Vibrating Wire transducers
  • Stainless steel or fiberglass connecting rods
  • Groutable or hydraulic anchors for various ground types
  • Head assembly compatible with manual or automated readout
  • Rugged, waterproof construction (IP68)
  • Long-term stability in harsh geotechnical environments

Detailed Description

How it Works (MPBX Principle)

The Multi-Point Borehole Extensometer (MPBX) measures the relative displacement between a fixed 'Reference Head' at the surface and one or more 'Anchors' locked into the ground at specified depths.

Rigid rods run inside a protective sleeve from each anchor up to the head. When the rock or soil mass moves, the distance between the anchor and the head changes. This movement pushes or pulls the rod, which actuates a Vibrating Wire transducer located in the head assembly, providing a precise reading of deformation for that specific depth zone.

Anchor Types for Different Geology

Successful monitoring depends on the anchor gripping the ground securely. We offer distinct types:

  • Groutable Anchors: The standard choice for downward-directed holes in rock or soil. The entire borehole is filled with cement grout, locking the rebar anchors in place.
  • Hydraulic / Borros Anchors: Ideal for soft soil or upward-directed holes (e.g., tunnel roofs). Prongs are hydraulically expanded to grip the borehole wall instantly without waiting for grout to cure.
  • Packer Anchors: Used in fractured rock where grout might flow away.

Why Multi-Point?

A single-point sensor only tells you *that* movement occurred, but not *where*. A multi-point extensometer reveals the depth and mechanism of failure.

For example, in a tunnel, Anchor 1 (1m deep) might show 5mm movement, while Anchor 3 (10m deep) shows 0mm. This proves the instability is shallow and the deep rock is stable. If Anchor 3 also showed movement, it would indicate a much more dangerous, deep-seated failure mode requiring immediate reinforcement.

Data Reliability

The G72-V550 utilizes Vibrating Wire transducers, which are favored for their frequency-based output. Unlike voltage signals, frequency does not degrade over long cable distances.

This makes the system immune to electrical noise from heavy machinery, pumps, or power lines often present in tunnels and mines, ensuring that the sub-millimeter data you receive is accurate and trustworthy.

Automation Ready

While the extensometer head can be read manually with a portable unit, it is designed for automation. The sensor head is compact enough to fit inside a protective cover, with cables routed to a central GL-DL16 data logger.

This allows for real-time remote monitoring of critical assets, sending automatic alarms to engineers if displacement rates exceed safety thresholds.

Available Models

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Specifications

Range
50, 100, 150 mm
Accuracy
±0.1% F.S.
Resolution
0.025% F.S.
Number of Points
1 to 6 (Standard)
Borehole Diameter
76mm to 100mm (Typical)
Rod Material
Stainless Steel / Fiberglass
Head Protection
IP68 Cover