Underground Service Location & Mapping Method

The process for detecting, marking, and mapping buried utilities will be carried out as follows:

  1. Identification of Utilities in the Target Area:
    • Locate all underground utilities that intersect or run alongside the designated area.
    • Mark the positions of these utilities.
    • Indicate the depth and direction of each utility.
  2. Identification of Utilities in the Servitude:
    • Locate other underground utilities within the servitude area.
  3. Detection Methods for Different Types of Utilities:
    • Electrical and Telkom Cables, Steel Pipes, and Conductive Utilities:
      • Utilize an electromagnetic transmitter and receiver to induce a signal onto the utility through methods such as direct connection (e.g., at valves, lamp posts), clamping (e.g., inside Telkom chambers, electrical substations), or induction scanning (when no contact points on services are available).
    • Storm Water and Sewer Lines:
      • Access points like manholes or kerb inlets will be used to locate these services.
      • A self-containing sonde, propelled down the pipe using a fiber flex rod, will transmit a signal, allowing the operator to determine the exact position and depth from above ground using a receiver.
    • Non-Metallic Pipes and Non-Conductive Services:
      • Non-metallic utilities, such as AC water mains and fiber optic cables, will be located using Ground Penetrating Radar (GPR).
      • If GPR cannot penetrate soil conditions or ground coverings, the Sewerin Combiphon may be used with written consent from the client.
      • GPR will be employed to locate services not detectable by electromagnetic methods.
  1. Marking of Located Positions:
    • Mark the positions of identified utilities on the ground using unique color-coded spray paint for each utility.
    • Include the following information:
      • Exact position of the utility.
      • Direction of the utility.
      • Depth at the marked position.
      • Ensure that all marked utilities are clearly shown to the contractor on-site.


Mapping of Buried Utilities:

  • A professional land surveyor typically conducts the surveying and mapping of located utilities.


Quality Control Measures:

  • To maintain the highest quality of work, the following procedures will be implemented:
    • Utilize highly experienced staff.
    • Ensure that all equipment is in good working order and subject to regular testing.
    • Obtain as much information as possible from other utility providers.
    • Foster close coordination between field staff and data processing staff to eliminate discrepancies in the information collected.



Description, Function and Accuracy

  • ELM Pipe locator, Locate conductive utilities, 5% of depth.
  • Ground Penetrating Radar, Locate non-metallic utilities, 10% of depth, dependent on soil conditions.
  • 33 KHz Sewer Sonde, Locate sewer and stormwater pipes, 5% of depth.


Ground Penetrating Radar Methodology:

Ground-penetrating radar (GPR) employs radiofrequency pulses to visualize subsurface structures. This method is non-destructive and excels in identifying various utilities, as it discerns differences in ground density, irrespective of the materials or content of pipes or cables. GPR operates by detecting reflected signals from subsurface utilities through the use of electromagnetic radiation in the microwave range of the radio spectrum (UHF/VHF).

The GPR system emits high-frequency radio waves into the subsurface using a shielded antenna with a predefined frequency range. Higher frequencies offer superior resolution but do not penetrate as deeply, whereas lower frequencies enhance penetration but reduce resolution. In practical terms, locating a utility deeper than 4 meters requires it to be larger than 1500mm in diameter to be effectively identified on the radar.

Several considerations are vital when employing GPR for utility detection:

  1. Local soil conditions: The transparency of soils to GPR waves varies, affecting the depth of GPR penetration.
  2. Anticipated utility depth.
  3. Utility size and type.
  4. Note that GPR signals cannot effectively penetrate reinforced concrete.

The depth range of GPR is constrained by factors such as the electrical conductivity of the ground, radar frequency, and the properties of the objects being detected. An increase in soil conductivity reduces penetration depth. Optimal results are achieved in dry, sandy soils, whereas moist, clayey soils or those with high electrical conductivity can limit penetration depth substantially.

The principal limitation of GPR performance lies in highly conductive materials, including clay soils, salt-contaminated soils, or soils with significant metal content. Performance may also be hampered by signal scattering in rocky terrains.

Selecting a utilities detection contractor demands careful consideration. Interpreting radar data (grams or display screens) is a subjective process, requiring considerable expertise in designing, conducting, and interpreting GPR surveys.

To enhance survey accuracy, it is strongly recommended to complement GPR with other utility location methods, including:

  1. Electromagnetic pipe and cable locators*
  2. Sondes** and tracer rods

*Note: Additional methods such as electromagnetic pipe and cable locators should be considered. **Sondes: Self-contained transmitters used for tracing utility pipes.