HDD Route Survey – GPR Scan Before Directional Drilling

Rates and page checked: 23 October 2026

What is a route survey for horizontal directional drilling?

Horizontal directional drilling lets a pipe or duct pass under a road, canal or railway without opening the surface. The catch is that the drill cannot see. A pilot head steered from the surface will cut through any cable or pipe in its path, and the reamer that follows makes the hole wider still.

A route survey for horizontal directional drilling is the check done before that happens. Our crews scan the ground along the planned alignment with ground penetrating radar, trace conductive lines with electromagnetic locators and mark everything found. The bore designer then knows where the existing services sit and can choose an entry angle, depth and exit point that keep clear of them.

This page covers the survey only. If you also need the bore drilled, our HDD drilling service uses our own rigs and crews and works directly from the survey findings.

Which parts of a bore need scanning?

An HDD bore path survey covers more than a single line between two points. We split it into four zones:

Entry pit and rig area

The rig, mud tanks and entry pit occupy a patch of ground at the start. Services under that patch can be hit by the pit excavation or crushed by the rig's weight, so it is scanned on a close grid.

Bore corridor

Radar lines run along the alignment and to either side of it, with cross-lines at intervals. A corridor rather than a single line matters because a steered bore can drift, and a service just off the design line is still at risk.

Exit pit and pipe layout strip

At the far end the drill emerges, and the product pipe is often laid out on the surface before pull-back. That exit area and the strip behind it are scanned like the entry side.

Crossing zone

Where the bore passes beneath a road, drain or embankment, we add extra lines, since services tend to bunch along kerbs, medians and drain edges.

How are road, canal and rail crossings surveyed?

• Roads and highways. Verges, footpaths and medians are scanned where traffic arrangements allow. Carriageway lanes may need a traffic plan or a night window, both charged separately from the survey rate.
• Canals, nalas and drains. Radar cannot work through standing water, so the survey concentrates on both banks and approach strips. Services that run along canal banks are common and get recorded carefully.
• Railway lines. Scanning on railway land depends on the permission the project owner obtains and the working window given. We cover the approaches on each side and the accessible parts of the crossing.
• Existing pipelines and duct banks. Where the bore must pass over or under a known large line, the survey confirms its position on both sides of the crossing.

A detailed look at crossing types on Gujarat routes is in our article on HDD crossing surveys for roads and canals, and the city-specific version is on the Vadodara HDD route survey page.

What can radar tell the bore designer, and what can it not?

Radar shows where services are in plan and gives an estimate of their depth. EM locating adds confirmation and depth readings for conductive cables. Together they answer the questions a bore designer needs first: how many services cross the alignment, roughly where, and at about what depth.

There are limits, and we state them openly:

• Depth reach depends on ground. Wet clay and saline soil absorb the signal; dry sandy ground lets it travel further. The report gives the depth actually reached on each section.
• Deep bores can pass below radar reach. A bore planned deeper than the radar can see is not cleared by the radar at that depth. Records, trial pits or boreholes at key points fill that gap, and we can provide pits or boreholes on request.
• Depths are estimates. They depend on the signal velocity used, so designers should keep a safety margin. Our note on GPR depth accuracy explains why.
• Small non-metallic lines are harder to detect, especially in wet ground. The report flags lower-confidence finds.

What does the drilling team receive?

1. Ground marking of each detected service at the pits and along the bore corridor, with approximate depth written beside it.
2. A crossing list naming each service that crosses the alignment, its position and estimated depth.
3. A signed report stating coverage, depth reach by section, no-access areas and the confidence of each find.
4. A depth profile along the alignment when the L-section GPR survey is ordered at ₹32 a metre.
5. CAD or GIS drawings if required – these are a separate item, quoted on their own.

With this pack the driller can set the pilot path, choose locator checkpoints and decide where to pothole a service before the reamer passes. It also gives the owner a record of what was known when the bore was designed.

How much does an HDD route survey cost?

HDD survey work follows our standard rate card. The plain route scan is ₹24 a metre; with the L-section depth profile it is ₹32 a metre. Each order is billed for at least 4 km, which is why grouping several crossings into one order saves money. For sites outside Delhi NCR, the bill for a project cannot fall below ₹1,00,000. GST is charged in addition.

Once an order passes 100 km, every metre is 25% cheaper; past 500 km the saving is 40%, and past 1,000 km it is 50%. Mobilisation, night shifts, traffic arrangements or permissions, and CAD/GIS drawing sets are quoted outside the metre rate. The full slab table is on our GPR survey price list.

Why choose a survey team that also runs HDD rigs?

We own 58 GPR systems and 18 HDD rigs and run both with in-house crews, without hiring machines or sub-letting work. Survey crews who also work alongside drilling teams know what a driller needs from a survey: clear pit marks, a usable crossing list and honest depth limits rather than a long report that says little.

Our trenchless utility mapping services are available whether or not we drill the bore. Many clients order the survey from us and use their own rig; others combine survey and drilling in one programme. Either way, the survey is a separate scope with its own report. Crews mobilise from Faridabad and have worked in 28+ States/UTs over 23 years.

What should you send before booking?

• The planned alignment as a KML or drawing, with entry and exit points marked.
• The product pipe or duct size and the intended bore depth.
• What each bore crosses – road, canal, drain, railway – and its approximate length.
• Any utility records from road authorities or service owners, even if incomplete.
• Working-hour limits and permissions already in hand.
• Whether the work order asks for an L-section or for CAD/GIS drawings.

For route-wide scanning before open-trench work rather than boring, see our pre-excavation utility scanning service.