d-Cable Geotechnical Instrumented Cable

YieldPoint’s d-Cable technology provides engineers, technicians, consultants and contractors with a digital instrumented 7-strand cable for geotechnical monitoring. This instrument tracks how the load develops its own length of 7-wire stand cable bolt over time. It allows a reliable assessment of the Factor of Safety against cable rupture. The instrument is applicable to cable bolts, ground anchors, tendons, and tie-backs used in all types of mining and civil projects. It has the potential to help predict the risk of catastrophic structural failure: in fact d-Cable data can enhance many aspects of engineering design, installation quality control, long-term operation assessment, and rehabilitation. Click here for a case study.

The d-Cable is indistinguishable from a regular cable and deployment simply involves replacing a regular cable with its instrumented equivalent. During cementing/grouting no special procedures need to be followed. The readout head of the d-Cable has the same diameter as the 7-wire strand itself, and therefore grips and a jack can be applied over the readout head if the cable is to be plated. If no face-plate is required the readout head can simply be recessed into the collar of the hole.

Features:
  • Instrumented 7-wire strand cable applicable to plain strand, bulb (Garford) cables
  • Applicable to grouted cables and cables spun in resin
  • Both Head-at-Collar (HAC) and Head-at-Toe (HAT) configurations possible
  • HAT configuration routes leadwire through a continuous steel tube
  • Available with mm or tons readout, please specify your preference
  • Available with 1 (d1Cable) to 6 (d6Cable) strain gauges
  • Microcontroller provides output directly in load (tons) or displacement (mm)
  • Individually calibrated, calibrations sheets available
  • Immunity to hostile environment
  • High survivability to shock and vibration
  • Easy to install and maintain
  • Digital (d-Tech) instrumented cable with RS485 signal out
Technology:

The d-Cable is based on miniature inductive strain gauges small enough to be recessed into a surrogate tubular king-wire. The gauges are configured with custom base-lengths between 200mm and 2,000mm. When the ends of the strain-gauge are secured (usually swaged) the instrument will measure how a certain length of the cable bolt is stretching in response to load. The base-length between the ends of the strain-gauges is specified by the customer. During manufacturing the entire strain-gauge array is independently manufactured and calibrated and then recessed into the king-wire and swaged in place.

The technology can be manufactured in HAC or HAT configurations. The HAT configuration is suitable for cables that are installed with a face plate, and the leadwires are returned through a continuous stainless steel tube.

Manual readout:

YieldPoint’s low cost geotechnical d-Reader readout unit or the new d-TAB. Both provide the temperature and displacement data directly in oC and mm.

Data-logging:

Data from the d-Cable can be collected using YieldPoint’s d-Logger dataloggers (d1Logger and d4Logger). Data can be download by any computer device running Windows including the convenient d-TAB.

Automated data retrieval:

Clusters of instruments (4 per Logger) that are monitored using YieldPoint’s d4Logger can be wirelessly networked using:

  • dMesh: a 900MHz wireless mesh solution.
  • IoT GateWay if Ethernet is available

Case study 1: Tieback monitoring in Toronto

7-wire strand cables are widely used as tiebacks in civil engineering projects. YieldPoint has worked with Monir Precision Monitoring of Toronto, ON, to monitor tiebacks installed in the foundation of the 41-story BISHA condominium project.

The load and displacement profiles along the tiebacks were successfully monitored both (i) as the tiebacks were post-tensioned to 70% the capacity of the steel strand and (ii) as the foundation was fully excavated. Results for both tie-backs were similar, and only changed minimally in the period after post-tensioning.

The Load in the tieback recorded at 1min intervals during the post-tension process.

The project has recently topped out at the 41st story.

Case Study 2: Monitoring of a cable Bolt array

load and displacement on a full ring of cables around a development drive was determined using a YieldPoint’s d-Cables and d-EXTO at a Mine in Queensland Australia. The d-Cables can be used to measure both displacement and load. By contouring deformations the data from instruments can be easily compared with results from numerical simulations. In this case deformation was concentrated in one wall of the drive.