Typical applications include:

Monitoring settlement in foundations.
Monitoring subsidence above tunnels and mines.
Monitoring heave in excavations. Monitoring the stability of tunnels and other underground openings.
Monitoring deformation in abutments and walls.

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Specifications
Operation
Downloads

ANCHORS
Groutable Anchor	51815852	Made from rebar, 19 x 365 mm (0.75 x 14.5″)
Hydraulic Anchor	51703952	Double-acting hydraulic anchor drives 150 (6″) mm prongs into soil. 32 x 620 mm (1.25 x 24.5″). Requires hydraulic tubing & pump

FIBERGLASS RODS
Fiberglass Rod	51815855	Fiberglass rod has a diameter of 5 mm (3/16″) and is supplied in continuous lengths
Protective Tubing	51815860	Protective polyethylene tubing is supplied in continuous lengths
Rod Completion Kit	51836240	Rod completion kit includes components for top and bottom of rod. Order 1 kit per anchor

STAINLESS STEEL RODS
Stainless Steel Rod	51704310	Stainless steel rod has a diameter of 6.4 mm (0.25″) and is supplied in 10’ lengths, each threaded and tapped for assembly
Protective Pipe	51704321	Protective pipe is supplied in 10’ lengths and includes couplings. Requires PVC solvent cement, which can be obtained locally
Rod Completion Kit	51836210	Rod completion kit includes components for top and bottom of rod. Order 1 kit per anchor

MECHANICAL REFERENCE HEAD
Single-Point Head	51836110	Single-point head works with 1 rod and anchor
Multi-Point Head	51836120	Multi-point head works with up to 6 rods and anchors. Readings are obtained with depth micrometer
Digital Depth Micrometer	51809620	Digital depth micrometer displays readings in inches and millimeters. 150 mm (6″) range, 0.01 mm (0.001″) resolution

ELECTRIC REFERENCE HEAD
Single-Point Head	51836130	Single-point head works with 1 rod and anchor
Multi-Point Head	51836140	Multi-point head works with up to 6 rods and anchors
VW Sensor, 60 mm range	52636305
VW Sensor, 100 mm range	52636325
VW Sensor, 200 mm range	42636200
Potentiometer, 60 mm range	51836152
Potentiometer, 100 mm range	51836154

SIGNAL CABLE
Signal Cable, 4-Wire	50613824	For one VW sensor
Signal Cable, 6-Wire	53102900	For one potentiometer
Signal Cable, Multicore	Contact Factory
Universal Terminal Box	57711600	For use with VW Data Recorder. Not required with data logger. Splashproof fiberglass box is 290 wide x 345 high x 135 mm deep (11.5 x 13.5 x 5.25″ )

INSTALLATION ACCESSORIES
Pipe Adapter	51835170	Optional adapter for anchoring reference head to 76mm (3″) diameter steel pipe installed at collar of borehole
Flange	51836175	Optional adapter for anchoring reference head to concrete pad at borehole collar. 190 mm (7.5″) plastic flange with 152 mm (6″) bolt circle
Grout Tubing	50721008	Used to deliver grout from the grout pump to the borehole. 12.7mm OD (0.5″) polyethylene tubing rated for 30 bar (425 psi)
Hydraulic Tubing	51702701	Used to activate hydraulic anchors. 6.35mm (0.25″) nylon tubing filled with oil
Hydraulic Anchor Tools	51704600	Hydraulic pump with gauge, T-connection, oil volume indicator, 1 gallon of oil, and adapter for filling hydraulic tubing
Spare Nut & Ferrule	51703950	Replacement hardware for connecting hydraulic tubing to anchor

VW Displacement Sensor Specifications

VW DISPLACEMENT SENSORS
Sensor Type	Vibrating wire. A built-in thermistor provides temperature measurements
Thermistor	3k Ohms at 25 °C
Over-Range	Range + 20%
Resolution	0.025% FS
Calibration Accuracy	±0.1% FS
Non linearity	<0.5% FS
Frequency Range	1650 – 2700 Hz
Nominal zero value	1850 Hz
Waterproof Rating	Waterproof crackmeter is rated to 16 bar (232 psi)
Diameter	13mm in diameter.

Components of a rod extensometer include anchors, rods with protective tubing, and a reference head. The anchors, with rods attached, are installed downhole. The rods span the distance between the anchors and the reference head, which is installed at the borehole collar. Measurements are obtained at the reference head with a sensor or a depth micrometer, either of which measures the distance between the top (near) end of the rod and a reference surface.

A change in this distance, found by comparing the current measurement to the initial measurement, indicates that movement has occurred. Movement may be referenced to a downhole anchor that is installed in stable ground or to the reference head, which can be surveyed. The resulting displacement data can be used to determine the zone, rate, and acceleration of movements, or to calculate strain.

Multipoint Monitoring

The rod extensometer can monitor up to six points along the borehole. The number of monitored points is limited by the size of the borehole, the type of anchor used, the diameter of the rods, and the amount of tubing required for grouting and activating anchors. A two-point extensometer typically requires a 60 mm (2.4 in) borehole; a four-point extensometer requires a 76 mm (3 in) borehole; and a six-point extensometer requires a 96 mm (3.8 in) borehole. Borehole size for packer anchors depends on number of anchors.

Anchors

Two types of anchors are available: the groutable anchor is suitable for rock and the hydraulic anchor is suitable for soils.

Rods

Rods are made of fiberglass or stainless steel. Extensometers using 3/16-inch fiberglass rods can be pre-assembled at the factory, coiled, and shipped to the site, ready for installation. In general, fiberglass rods are easier to install in confined areas, such as tunnels. Fiberglass rods also resist corrosion and are preferred over stainless in alkaline environments. Extensometers using stainless rods must be assembled on site. Stainless rods are stiffer than fiberglass rods of the same diameter and are preferred when compression, rather than extension, is likely, or when longer lengths of rods are required. Protective tubing or protective pipe is installed with the rods to prevent bonding between the rods and grout.

Readout Options

Extensometer measurements can be obtained with a depth micrometer or a sensor. The depth micrometer is suitable when there is easy access to the reference head. However, when access to the reference head is difficult or where real-time or continuous monitoring is required, a sensor is the better option.

Rod Extensometer