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1GEODATA Group / Hans-Kudlich-Strasse 28, A-8700 Leoben / Phone: +43-(0)3842-26555-0, Fax: -5 / office@geodata.at / www.geodata.com

Rod Extensometer

For lengths up to approx. 130 m

High measurement accuracy

Simple assembly

Automatic data acquisition possible

HIGHLIGHTS

Field of Application

Extensometers are among the most frequently used instruments for measuring the axial deformation along a borehole. They are used for monitoring support and anchoring systems in slope protections, open cuts, underground constructions etc. or to observe settlement and sliding. Several single extensometers can be bundled into multiple extensometers with anchoring points in different depths.

In this way, it is possible to identify the areas where movement has occurred. The magnitude and progression in time of these movements are valuable indicators for the stress in the construction and the success of the stabilising measures.

Principle of Operation

The anchoring part is mounted in the borehole such that it will follow even very small movements in the rock or the ground. It is solidly attached to a measuring rod which transmits the movement to a pin in the measurement head which is mounted at the mouth of the borehole. In this way, the relative movement between the anchor and the mouth of the borehole can be established by sensing the distance between anchor and measurement head.

date: 03/2008

4-fold extensometer-head in anchor beam

Schematic assembly

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Rod Extensometer

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GEODATA Group / Hans-Kudlich-Strasse 28, A-8700 Leoben / Phone: +43-(0)3842-26555-0, Fax: -5 / office@geodata.at / www.geodata.com

This is performed by a dial gauge or electric displacement transducer. This measured value can be converted to an elongation L/L. For protection and for mechanical installation reasons, the measuring rods run inside a pipe between anchor and measuring head. This pipe is designed not to influence the movement of the anchor and the rods, which would cause erroneous readings.

Construction

An extensometer fundamentally comprises an anchor, the measuring rods in the protective pipe and the measuring head with measuring pin. The selection of the anchor type is determined by the rock or the ground in which it must be anchored. When using ribbed steel bars for anchoring parts, the entire borehole is filled with a cement suspension, in which case it is important to ensure that the stiffness of the hardened injection material matches that of the soil, especially with soft soils, by adding suitable additives. Swellex anchors can be used in heavily fractured rock of sufficient strength. Anchoring parts fitted with packers are suited for loose soils and gravel. The latter should be used especially where the borehole lengths between the anchoring parts may not be filled.

GEODATA extensometers are fitted with fibre glass measuring rods as a standard. The individual rods (l = 3 m) are joined by crimped sleeves and can be shortened to any length. We also offer stainless steel, galvanised steel or Invar steel on request.

The measuring heads are designed to allow easy combination of single extensometers to create multiple extensometers.

Data Acquisition

The measurements can be performed either manually, using dial gauges, or by means of electrical displacement transducers. The GEODATA information software KRONOS is available for analysis of the data. The software can compile lists and also graphs highlighting cross-section related change against time.

Surface-extensometer with electric displacement transducers

Reading of extensometers with elektric displacement transducers

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Rod Extensometer

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GEODATA Group / Hans-Kudlich-Strasse 28, A-8700 Leoben / Phone: +43-(0)3842-26555-0, Fax: -5 / office@geodata.at / www.geodata.com

Technical Specifi cation

Extensometer headMaterial stainless steel, brassAdjustable dial gauge stop +/- 100 mm, +/- 150 mm optional

Measuring rodStandard length 3.0 m, 1.0 m

- FibreglassDiameter 10 mmAssembly squeezed brass sleeves Coefficient of thermal expansion 10 x 10-6 mm/m °C

- Stainless steelDiameter 8 mmAssembly screwed, M8 Coefficient of thermal expansion 16 x 10-6 mm/m °C

- Galvanised steelDiameter 8 mmAssembly screwed, M8Coefficient of thermal expansion 12 x 10-6 m/m °C

Protective tubeMaterial PVCDiameter 20 mmAssembly glued with PVC-sleevesDelivery length 3.0 m

Anchoring system Standard HeadMaterial Tenax TX 55 Tenax TX 55, GeotextileAnchoring length 500 mm 700 mmDiameter 20 mm 110 mmQuantity (multiple extensometer) max. 6 max. 5

Borehole diameterAnchoring points per borehole 1 2 3 4 5 6Min. borehole diameter (mm) 55 75 85 110 120 130Diameter for head 127 127 127 127 127 -

Dial depth gaugeType mechanical or electricalResolution ± 0.01 mm

System components right to left:Measuring head with protective cap, dial gauge stop with adjustable measuring range, fi breglass measuring rod with coupling / protective tube with coupling / anchor part

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Rod Extensometer

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GEODATA Group / Hans-Kudlich-Strasse 28, A-8700 Leoben / Phone: +43-(0)3842-26555-0, Fax: -5 / office@geodata.at / www.geodata.com

Displacement transducer (optional)Measuring range 50 mm 100 mm; 250 mm optionalLinearity ± 0.1 % FS (without linearization)Sensor type PotentiometerOutput signal optional 4 to 20 mASealing class IP 65

Measuring heads with electric displace-ment transducers for 3-fold extensometer

The following other datasheets are associated with this datasheet:

Services: Geotechnical Monitoring - Installation, Data Acquisition and EvaluationSystems: DAMOS - Automatic Data Acquisition SystemSoftware: KRONOS Tunnel Information System