On many UAE sites the default way to find buried services is to dig for them: hand-dug trial pits at intervals along a trench route, or at the corners of a plot. It is a reasonable instinct. A pit gives you a certain answer: you can see the service, measure its depth and read the marker tape. The weakness is that it gives that answer only at the spot where you dug. This guide compares trial pits with a GPR ground survey, and explains why they work best together.
What a trial pit tells you
A trial pit is direct evidence. When it exposes a service you know what it is, how deep it is, what it is made of and which way it is heading at that point. Nothing else gives that level of certainty, and many service owners and consultants require pits to confirm the position of critical assets before machine excavation near them.
What a pit does not tell you is what lies between pits. A service that crosses the route between two pits, or turns, or was never on the drawing, is invisible until the excavator finds it. Pits are also slow, disruptive on finished surfaces, and not risk-free: hand digging a pit near a live cable still means digging near a live cable.
What a GPR ground survey tells you
A ground penetrating radar survey covers the whole area. We push the Proceq GS8000 over the site in a grid, in two directions so services running either way are crossed, and record reflections from anything that contrasts with the soil. The output is a map of what is in the ground across the survey area: positions, directions and estimated depths of cables, pipes, ducts, chambers, tanks and voids, metallic or plastic.
What radar does not give you is identity or certainty. It shows an object at a position and depth, but not whether it is a water main or a telecom duct, and its depth is an estimate. In saline or saturated ground it can lose deeper targets altogether. Our guide to GPR depth in UAE ground explains why.
Side by side
- Coverage: a pit covers one spot; a survey covers the whole route or plot.
- Identity: a pit shows what the service is; radar shows that something is there.
- Depth: a pit gives a measured depth; radar gives an estimate that depends on the ground.
- Plastic and dead services: a pit finds them if you dig in the right place; radar finds them anywhere in the survey area, which a cable locator cannot.
- Disturbance: a pit breaks the surface and has to be reinstated; radar leaves nothing but paint.
- Risk: digging a pit near a live service is itself a strike risk; radar is non-contact.
- Speed: one pit can take as long as surveying a trench corridor.
Why the best plans use both
The two methods fail in opposite ways, which is why they belong together. The survey answers the question pits cannot: what is between the pits, and is there anything nobody expected. The pits answer the question the survey cannot: exactly what is this line and exactly how deep.
Used in that order, the survey decides where to dig the pits. Instead of digging at fixed intervals and hoping, you dig where the radar shows a service crossing the route, at the points that matter for the excavation. Fewer pits, in the right places, and every pit confirms something specific.
Survey first, then pit where the survey shows a service crossing the dig or where the drawings and the survey disagree. That is usually fewer pits than a fixed-interval plan, and each one answers a real question.
An example of the sequence
Take a new drainage trench across an industrial yard in Sharjah or Al Quoz, with authority drawings showing one water line and one power feed crossing the route. A fixed-interval plan might put a pit every so many metres and hope the crossings fall in them. Surveying the corridor first shows where the two recorded services actually cross, and often shows one or two more that are on no drawing, such as a private feed to a site office or an old irrigation line. Pits then go exactly where each crossing is, confirming identity and depth at the points the excavator will meet. The crew digs the rest of the trench by machine, with hand digging at the marked crossings.
When pits are required anyway
On many sites, trial pits are a condition rather than a choice. A service owner's NOC may require hand-dug pits to expose an asset before machine work nearby, and a main contractor's method statement may specify them. A survey does not remove any of those requirements. It helps you meet them by showing where to dig, which reduces the number of blind pits that find nothing.
Where cable locators fit
A third tool often appears on these sites: the handheld electromagnetic cable locator. It detects the field around conductive services and is quick for tracing a known live power cable, but it cannot see plastic pipes, empty ducts or dead cables. The comparison is covered in GPR vs cable locators. We use the GS8000 for our surveys and do not offer a locator sweep as a cheaper substitute for a radar survey.
Choosing the right mix for your site
- Short trench in a well-recorded area: a corridor survey, plus pits at any service crossings it shows.
- Industrial plot with no reliable records: a full-area survey first, because pits at intervals will miss most of what is there.
- Landscaped areas with irrigation: a survey, because plastic irrigation lines are dense and shallow and pits at intervals will cut some of them.
- Work near a critical asset named in an NOC: pits as the condition requires, placed using the survey.
- Deep excavation on saline or reclaimed ground: survey to the depth the ground allows, and plan pits or other checks for anything deeper.
What you get from us
Services are painted on the ground with estimated depths during the visit, and the survey report follows within 24 hours, with any areas where the ground limited the reading clearly marked. For larger sites we provide a marked-up drawing over your site plan, which makes a pit plan easy to agree. See GPR ground scanning for coverage across the UAE, or underground utility survey in Dubai for Dubai sites. If NOCs are part of your job, read NOCs and the GPR survey in Dubai.