If you need a pipe, duct or cable in the ground, there are two broad ways to get it there. You can dig an open trench, lay the pipe and backfill it, or you can install it underground with a trenchless method like directional drilling, and never break the surface between the launch and reception points. The right answer is not always the same, so it is worth being straight about when each one wins.
When open-cut is the sensible choice
Open-cut is simple, and for the right job it is hard to beat on price. If the ground is open, the pipe is shallow, the run is short, and there is nothing important sitting above the line, digging a trench is quick and cheap. There is no specialist plant to mobilise and no guidance system to pay for. For a straightforward service across a field or a verge, open-cut often makes the most sense, and we will tell you so.
Where the trench gets expensive
The trouble with a trench is that the digging is only part of the cost. The bigger the obstacle you are crossing, the more the open-cut price climbs, and it adds up in ways that are easy to miss.
- Crossing a road or a railway means traffic management, possible closures, and the asset owner’s approval before you touch anything. On a motorway or a live railway, an open dig is usually a non-starter.
- Deep pipes mean deep trenches, which mean shoring, more spoil to handle and dispose of, and more reinstatement.
- Reinstating a carriageway, a footway or a landscaped area to the standard the owner demands is a real cost that is easy to underestimate.
- Rivers, canals and environmentally sensitive ground add consents, working windows and mitigation that a surface dig makes harder, not easier.
By the time you add traffic management, reinstatement and the disruption to everyone using the road or land above, the “cheap” trench is often not cheap at all.
Where trenchless wins
Directional drilling and the other trenchless methods come into their own exactly where the trench struggles. Because the pipe goes in from a launch pit on one side to a reception pit on the other, the surface in between is left alone. That means:
- Roads and railways stay open, so there is little or no traffic management and no closure of the asset.
- The reinstatement bill drops to two small pits instead of a full-length trench.
- Deep and long crossings are drilled in one pass rather than dug as a deep trench.
- Rivers, canals and protected ground are crossed underneath, well below the bed or the sensitive surface.
On the right job the saving is dramatic. On one drainage outfall we drilled rather than tunnelled, the client saved around £1 million because the crossing could be done as a drilled bore instead of a far more expensive dig.
How to work out which is cheaper for your job
There is no single rule. It depends on depth, length, ground and what sits above the line. The way to compare properly is to price the whole picture on both options, not just the metres of pipe, but the traffic management, the reinstatement, the consents and the disruption. That is the comparison we do for free with every quote. Send us your drawings and levels and we will tell you plainly whether to dig it or drill it.
For more on how drilling is priced (and why it is not a simple per-metre figure), see our guide to directional drilling costs, or read about horizontal directional drilling itself.