Extensometers

Extensometers

Are used to locate and measure movement along a single axis.

Magnetic Extensometers

  • Are used to measure and locate settlement and heave in soil and rock.
  • Typically used in excavations, embankments and foundations, behind retaining structures, and above tunnels and underground openings.
  • Comprise of a central access tube along the length of which magnetic targets are placed.
  • Are read manually using a Reed Switch Probe which is drawn through the central access tube, emitting an audible beep when it passes through a magnet. 
  • Readings are referenced to the base magnet and data obtained identifies the depth and position of settlement/heave as well as the total amount of movement.
  • Designed to be simple and accurate, and provide long term reliability at a low cost.
  • Can easily be extended upward with embankment construction or shortened with excavation.

Rod Extensometers

  • Are used to measure and locate settlement and heave in soil and rock.
  • Typically used in excavations, embankments and foundations, behind retaining structures, and above tunnels and underground openings.
  • Consist 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. 
  • Can be read either manually using a depth indicator or dial micrometer, or automatically using an electrical displacement sensor.
  • Readings are referenced to the reference head and data obtained identifies the depth and position of settlement/heave as well as the rate and total amount of movement.

Soil Extensometers

  • Are used to measure lateral and longitudinal deformation of soil and rock.
  • Typically used in embankments, retaining walls and abutments, foundations, natural and cut slopes, quarry and mine excavations, and rock formations.
  • Consist of a displacement transducer connected to an extension rod and fixed between a pair of anchor beams. As movement occurs, the rod is moved within the housing. This movement is recorded by the displacement transducer. 
  • Are read automatically using the displacement transducer.
  • Sensors can be installed in a chain, with anchor bars connected together.
  • Data obtained identifies amount and location of displacement as well as the rate and total amount of movement.

Tape Extensometers

  • Are a portable device used for measuring displacement between reference eye-bolts fixed to a structure.
  • Typically used in tunnels and shafts, retaining walls and abutments, natural and cut slopes, quarry and mine excavations, and embankment dams.
  • The instrument consists of a precision punched steel tape incorporating a repeatable tensioning system and digital readout. Both the body and end of the tape have hooks which connect to eye-bolts between which the readings are to be taken.
  • The instrument is read manually. The user will connect each end of the tape to an eye-bolt, tension the instrument to the correct tension, and record the reading on both the tape and the digital display.
  • Data obtained accurately identifies displacement between points over time.

Monitoring Surveys

Monitoring Surveys

Are used to optically measure the movement of points on a structure in one or more dimensions.

Total Station Surveys

  • Are used to accurately measure the three dimensional location and movement of survey points.
  • Typically used for monitoring buildings during excavation of tunnels or shafts, and to assess the stability of dams, embankments and rock faces.
  • Surveys can be conducted manually, or automated total station networks can be set-up to automatically take readings from survey prisms.
  • Readings will accurately give the location of each point in three dimensions, from taking additional sets of readings the movement of the point in three dimensions can be calculated.
  • Points can easily be added or removed from the survey network.
  • The system is optical so relies upon a line of sight between the total station and the survey points.

Precise Levelling

  • Is used to accurately measure the vertical movement of survey points.
  • Typically used for monitoring buildings and utilities during tunnel or shaft excavation, dams, and embankments.
  • Precise levelling is undertaken manually.
  • Readings will accurately give the vertical height of each point, and from taking additional sets of readings the vertical movement of the point can be calculated.
  • The system is optical so relies upon a line of sight between the level and the levelling points.

Convergance Monitoring

  • Is used to measure the displacement between two points on a structure.
  • Typically used for monitoring tunnels and shafts, retaining walls and abutments, structural movement, quarry and mine excavations, and dams.
  • Readings are undertaken manually using either a tape extensometer, or a laser distance meter.
  • Data obtained will give the distance between the two points, and from taking additional sets of readings, the movement can be calculated.

Load Cells

Load Cells

Are used to measure loads in rock bolts, cable anchors and tendons, and loads in pull-out tests on trial anchors.

Upon recommendation by RST Instruments, R L Geotechnical Ltd. was contracted by AD Resources (Ghana) Ltd. to install 28no. vibrating wire piezometers at one of the Tailings Storage Facilities at the Tarkwa Gold Mine, operated by Gold Fields Ghana. 

The vibrating wire piezometers were installed into standpipes, with the drilling and installation of these completed by AD Resources Ltd. prior to the arrival of R L Geotechnical Ltd. Each VW piezometer had it’s own RSTAR DT2011B Node which transmitted data via the RSTAR radio link to one of the two FlexDAQ Hubs, one installed at either end of the tailings dam. Each DT2011B was housed neatly within a secondary enclosure with enough cable left to allow for the dam to be extended upward in the future. Due to the great distances between the DT2011B Nodes and the FlexDAQ Hubs, Yagi antennas were used at some of the locations. these were mounted neatly onto the DT2011B secondary enclosure or on a pole next to it to ensure good a good signal between the DT2011B Node and its corresponding FlexDAQ Hub.

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