GPR Survey for HDD Contractors: Pre-Drilling Scans

What does a GPR survey for HDD contractors cover?

The full bore corridor from entry pit to exit pit, with a margin around both pits and the approach where the rods go down. It also covers the full width of every road, drain or service crossing on the way. The aim: no line on the bore path that the driller does not know about before the pilot hole starts.

• Bore corridor: scanned across and along, wide enough to allow for steering and small route changes.
• Pits: scanned with a margin, because pits are often moved on the day to avoid a gate, a tree or a parked vehicle.
• Crossings: roads, culverts and drains scanned along their full width, where services from several owners tend to converge.
• Marks: paint on the surface for every line found, giving an approximate depth and the service type when we can tell it.

If the client or the permission requires one, an L-section is drawn through the bore, plotting every detected line against the design profile. As a survey method, ground penetrating radar (GPR) suits this work: the antenna fires short pulses as it rolls, and the echoes image the subsurface along the shot.

Why do drilling contractors bring in a separate survey team?

Because the strike risk, the client's specification and the permission conditions sit with the drilling contractor, and an independent survey record protects all three. Many telecom, gas and power clients now ask for a pre-drilling scan report with every bore. Road owners increasingly want existing services shown on the drawing before they approve a crossing.

A separate survey crew also keeps the rig moving. While the drill team works on today's shots, our crew scans the next ones.

We are drillers ourselves. Besides its survey fleet, Mezux Touch owns and runs 18 HDD rigs. The engineers who scan therefore know what drillers want: clear marks, honest depths and a flag on anything uncertain. To see that side of our work, read our HDD drilling details.

Which bores do contractors ask us to scan most?

Short road crossings for fibre ducts make up the bulk, followed by gas service and distribution crossings, power cable crossings under roads, and longer bores under drains, culverts and medians. Each type has its own pattern of risk.

• Fibre duct crossings: short, shallow and numerous, often in streets already full of older ducts. Existing optic fibre is the most likely thing to hit.
• Gas crossings: clients ask for the clearance to every other service to be shown, so an L-section is common.
• Power cable crossings: live cables can be traced passively with a locator, which adds certainty to the GPR marks.
• Drain and culvert crossings: the culvert itself is easy to see; the services bunched around it are not.
• Rail and canal crossings: scanned only under the owner's permission and site rules, with records doing more of the work at depth.

What does the drill crew receive?

Marks on the ground before the rig arrives, and a short survey pack per shot that the site engineer can check against the bore plan.

Most of our contractor work is on fibre and duct routes for network roll-outs; for that side, see details of telecom operator projects.

How quickly can a crew start, and how does a job run?

For a confirmed Delhi NCR order, expect the crew on site that day, or the business day after at most. Outside the NCR, an engineer resident in that city begins at once, inside one business day. Our crews are our own staff, never sub-let, so the person who scans is the person who answers your questions.

1. Bore list: you send the shot list with chainages, pit locations, design depth and product size.
2. Desk check: our engineer reviews it with any records you have and plans the scan corridor.
3. Field scan: radar runs along and across every shot in real time, while live cables and metal lines are traced electromagnetically.
4. Marking: services painted on the ground and recorded with photos.
5. Hand-over: marks shown to your site supervisor, and the shot pack sent the same or next day.

On busy roads we can scan at night if the permission allows only night work. For a worked example of how this runs on NCR roads, read HDD Route Survey in Delhi NCR.

What are the limits of a pre-drilling scan?

Radar picks up most services within the first one to three metres, soil permitting. Where a bore is designed below that, records, chamber readings and potholes must fill in what the radar misses. Wet clay and saline ground have high electrical conductivity and shorten the range. Plastic pipes give weaker echoes than metal ones. Large or deep sewers may be below the radar's reach.

Every shot pack records how deep the scan reached, which tells the crew what is proven and what still needs checking. On deep crossings we recommend:

• measuring crown and invert depths in nearby manholes and chambers;
• a pothole at the closest crossing, by hand or vacuum excavation;
• shorter tracker reading intervals across each marked line;
• watching drilling fluid returns closely where old trenches run parallel to the bore.

Frac-out and cross-bore checks

Two problems turn up after drilling, not during it. A frac-out happens when drilling fluid escapes along a weak path, often an old backfilled trench, and surfaces in the road or a basement. A cross bore happens when the new duct passes through a sewer or a drain without anyone noticing. The survey helps with both: backfilled trenches show up on the radargram as disturbed ground, and sewers and drains are marked with their chambers. Where a bore runs close to a sewer, a camera check after pull-back is a sensible step.

What do contractors pay?

₹24 per metre for a standard pre-drilling scan and ₹32 per metre with an L-section, GST extra. The minimum order is ₹50,000 in Delhi NCR and ₹1,00,000 elsewhere in India. Long programmes get whole-order discounts: 25% above 100 km, 40% above 500 km and 50% above 1,000 km. There is no separate kilometre minimum.

Drilling firms with a run of short shots tend to bundle them into a single order, paying the minimum once instead of shot by shot. To test your own numbers, try the Mezux GPR cost calculator.

How do you send us a bore list?

Send the shot list, the route drawing or KMZ, and the client's survey specification; that is enough for a written quote. Add the design depth, product diameter and pit coordinates for each shot if you have them. Missing details are filled in on the desk check.

Fill in the form here or send the files on WhatsApp to +91 99100 10209, and we will get a written quote for your project to you.

Frequently asked questions

Are the entry and exit pits scanned, or only the bore?

Both, and the pits get a margin round them, since crews often move a pit on drilling day.

Can you scan ahead of our rig on a running programme?

Yes. Our crew works a few shots ahead of the drill team so marks are ready when the rig arrives.

How deep can a pre-drilling scan see?

One to three metres in most soil conditions. Each shot's report gives the depth the scan reached, and below that we advise potholing.

Do you supply an L-section for every shot?

Only where it is ordered, at ₹32 per metre. Standard marks with depths are ₹24 per metre.

Can you work at night?

Yes, where the permission or traffic police require night work. Night work may be priced separately.

How does GPR detect a buried line?

Radar pulses reflect from each buried object and show as curves on the radargram, which also feeds underground utility mapping of the route. For the basics, see GPR scanning.

Written by Saniya Parveen · Technically reviewed by Rahul Rai · Updated 8 November 2026