Magnetic Extensometers
The Geosense® GEO-XM settlement system is a magnet extensometer system used typically to monitor settlement and heave in foundations, excavations and embankments.
Data received identifies the depth and position where settlement has occurred as well as the total amount of settlement.
It can also be installed behind retaining structures, such as sheet piles and slurry walls, and above underground openings, such as tunnels and shafts.
The system comprises a central access tube along which magnetic targets are positioned at various locations. Settlement is measured by the relative position of the magnetic targets using a Reed Switch Probe lowered down through the central access casing.
There are several variations to suit individual applications:
GXM-100 Central access tubing and spider magnets for use in boreholes
GXM-100P Central access tubing and settlement plates for use in fill
GXM-100T Central access tubing with telescopic joints for larger movement
GXM-200 Combined settlement/heave and inclination using inclinometer casing as the access tubing with spider magnets
GXM-200P Combined settlement/heave and inclination using inclinometer casing as the access tubing with settlement plates
GXM-200T Combined settlement/heave and inclination using inclinometer casing with telescopic joints for larger movement
GXM-300 Central access tubing de-bonded by an outer corrugated pipe with magnetic targets
GXM-300i Combined settlement/heave and inclination using inclinometer casing as the access tubing de-bonded by an outer corrugated pipe with magnetic targets
Reed Switch Probe
The Reed Switch Probe is used to determine the location of magnetic sensors in magnetic settlement systems.
When the reed switch passes through a magnetic field, it closes; completing a circuit and a buzzer is activated.
The elevation of the magnet target is read directly from the tape.
Borehole Rod Extensometer
The Geosense® GEO-XB2 borehole rod type extensometer range is used to measure and locate settlement, displacement and deformation in soil and rock.
It consists of a reference head and one or more in-hole anchors each of which is placed at a known depth and connected to the reference head by either a rigid or flexible rod running inside a flexible sleeve, which keeps the rod de-bonded from the grout.
As the soil or rock deforms the distances between the in-hole anchors change, as do the distances between the individual in-hole anchors and the reference head. The magnitude, distribution and rate of deformation can be accurately measured at the reference head.
The GEO-XB2 rod type extensometer range is available in a wide range of reference heads, anchors, rods and measuring sensors.
Digital Tape Extensometer
The Digital Tape Extensometer is a portable device used for measuring displacement between reference anchors fixed to an excavation or structure.
The instrument consists of a precision punched steel tape incorporating a repeatable tensioning system and dial gauge readout. The tape winds onto a reel, which incorporates a tape tensioning device and a digital LCD readout.
The body of the extensometer has a hook connector that connects to the first eyebolt. An identical hook on the free end of the tape connects to the opposing eye bolt. The user then tensions the instrument and records the readings from the digital LCD display. The measurements are not absolute, but relative to the previous measurement. This provides an accurate record of displacement over time.
These can be installed on a structure or in an excavation such as a tunnel or shaft.
Wire Extensometer GEO-DW300
The GEO-DW300 Wire Extensometer is designed to monitor the changes in distance between two anchor points and is available complete with vibrating wire displacement transducer. A stainless steel wire connects the transducer to the opposing anchor.
The mounting plate holds the transducer at one end and a pulley at the other end. A stainless steel wire connects the transducer to the opposing anchor. The pulley allows the transducer and anchor to be mounted on different planes, including perpendicular surfaces, up to 10m apart. The spring-loaded transducer keeps the steel wire tensioned.
Typical applications include monitoring cracks or displacements in civil structures.
Rotary Wire Extensometer GEO-XW100
The GEO-XW100 Rotary Wire Extensometer is designed to monitor the changes in distance between two anchor points up to a maximum of 30 metres apart.
It comprises a rotary potentiometric displacement gauge, an opposing anchor and a stainless steel wire that runs between the displacement gauge and the opposing anchor. With a wire extension kit, the length of the wire can be extended up to a maximum distance of 30 metres.
The displacement gauge is housed within a rugged steel enclosure with a mounting plate for horizontal or vertical mounting.
Two options for installation are available as follows:
- Exposed wire in combination with expansion anchor and eyebolt typically for attaching to rock or concrete.
- Wire running within a protective sleeve where the bottom anchor is mounted in the bottom cap at the end of the protective sleeve. The protective sleeves can either be mounted on posts above ground or buried typically used for slope and/or landslide monitoring.
VW Soil Extensometer
The Geosense® GEO-XS VW Soil Extensometer monitors lateral and longitudinal deformation of soil and different types of embankments and embankment dams.
It comprises a displacement transducer connected to an extension rod and fixed between a pair of anchor beams.
The assembly is housed in and protected by an external telescopic sleeve. To form a ‘Chain Extensometer’, Soil Extensometers are linked together, in series, using the anchor beams as connectors.
The internal sensing element is housed within an outer PVC sleeve which is sealed by O-rings at each end. The sleeve, with telescopic sections with O- ring seals, is extended along the whole length of the rod to the next anchor.
As structural movement occurs, the rod is moved within the housing. The shaft movement changes the tension in the sensor spring which, in turn, changes the tension in the Vibrating Wire.
Different combinations of anchor spacing (Gauge Length) and sensor range can we used to provide an optimum sensing accuracy and range. i.e. for maximum strain resolution, a shorter transducer length will provide the best results. For maximum deformation, use a longer transducer or a shorter gauge length.
Tunnel Profile Monitoring
The Tunnel Profile Monitoring System is a series of linked rods, fixed to the tunnel wall, to monitor deformation. A data logging system and related software is available to provide near real time displacement and generate a graphical representation of tunnel performance.
A system of linked arms is affixed to the tunnel wall. Each arm is fitted with a high accuracy displacement sensor and precision tilt meter. Spatial displacement of the pins and arms results in changed tilt and displacement readings. The data logger system automatically collects the data and transmits it to a computer. The computer then analyzes the data, and calculates the displacement profile for presentation.
The system is available in either open or closed loop configurations. The closed loop method is analogous to conventional closed end survey techniques, while the open loop must be referenced to a known location.