Walk-over Tracking
This is the most widely used locating system in HDD. As the name suggests, the locator follows the drill bit travelling underground by walking above it at the surface. The sonde (transmitter) inside the steering head and the receiver carried by the locator exchange signals every 0.001 seconds and fix the position.
The locator can therefore check the depth of the bit below the surface, its angle to the horizontal, which way the duckbill or bend sub is facing, and the ambient temperature at any moment. The maximum depth reachable with this system is limited by the signal strength of the sonde.
Components, limits and use on site
A walk-over system has three parts: the battery-powered sonde (transmitter) inside the steering head, the receiver carried by the locator, and the remote display in front of the rig operator. The sonde emits a magnetic signal at a set frequency; the receiver derives depth from the signal strength and the sonde's surface projection from the signal geometry. Pitch and roll arrive encoded within the signal, and the operator sees these values in real time to turn the head in the required direction.
The system's limit is signal strength. Typical sondes give reliable readings down to 15–20 metres; on deeper or very long crossings the signal weakens and the position becomes uncertain. High-voltage lines, railway tracks, metro lines and large steel structures add interference; in that case sondes of different frequencies are tried, or the project switches to a magnetic guidance system. Battery life is another limit: on long pilot bores the rods may have to be pulled back to change the sonde battery.
The advantages, on the other hand, are clear: set-up takes minutes, one locator can run it, no wire or surface array is needed, and it provides sufficient accuracy for the vast majority of urban HDD projects. On any route that can be walked at the surface, walk-over locating is the first choice; it is the standard method for natural gas, water and fibre-optic crossings beneath city streets. Deltek works with sondes and receivers of different frequencies and power classes; the choice of system and its depth limit are shared with the client at the tender stage on every project.
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