Beginner's guide
If you need a pipe, duct or cable put in the ground but cannot dig up what sits above it, a watercourse, a railway, a road, buildings or trees, and even things like gardens and fields, you need a trenchless method. This is a plain-English guide for anyone who has never done it before. It explains what each method is, what it is best at, and how to work out which one your job actually needs, with no jargon and no hard sell.
Trenchless simply means putting a pipe in the ground without digging an open trench along its whole length. Rather than excavating the entire route, the pipe is bored or driven underground from a small pit at each end, so the surface in between, whether that is a river or canal, a railway, a busy road, buildings, trees or a finished driveway, is left undisturbed.
It is sometimes called no-dig installation. The pay-off is less disruption, less reinstatement, and a safe way to cross things you are not allowed to dig up. There is also far less risk of striking an existing buried service, because the bore follows one controlled, surveyed line rather than opening up a long trench across everything in the ground. On the right job it also works out cheaper overall, even though the kit on site is more specialist than a digger and a gang.
Open-cut is the traditional way, dig a trench the full length of the route, lay the pipe, backfill and reinstate. It is fine in an open field with nothing in the way. It becomes slow, costly and disruptive the moment a road, railway, river or buildings sit on the line, because you then have to close, dig, support, backfill and resurface all of it.
Trenchless turns that into two small pits and a single bore underground. The road stays open, the river is untouched, and there is far less to reinstate afterwards. That is why for crossings, deep installs and anything sensitive, trenchless is usually both cheaper overall and far less hassle. We will still tell you honestly when a straight dig is the better answer.
The methods
There are a handful of trenchless methods, each suited to a different size of pipe, length of crossing and type of ground. Here is what each one is, in plain English, and what it is best at. Follow any of them through for the full detail.
The workhorse method. A steerable drill head bores a curved or level path underground, guided by a survey system, then the bore is opened out and the product pipe pulled back through it. Because it is steered, it can be aimed under a road, river or railway and brought back up exactly where you want it.
Best for: Steered crossings of almost any service or pipe, from a few metres to several hundred.
Read more →The simplest and usually the cheapest method. A torpedo-shaped pneumatic "mole" hammers its own way through the soil under compressed air, compacting the ground aside rather than removing it, and tows the new duct in behind. There is no steering, so accuracy is set by how it is aimed at launch.
Best for: Short, small service runs under a drive, garden, path or minor road in soft ground.
Read more →A steel casing is driven through the ground by a powerful pneumatic hammer at the launch pit. The casing protects the bore as it goes, which makes it well suited to loose, mixed or water-bearing ground where an open bore might collapse.
Best for: Larger steel casings under roads and railways, including in difficult ground.
Read more →Directional drilling fitted with a rock system, such as a dual-pipe All Terrain rig or an air hammer, to steer a bore through hard rock that ordinary drilling cannot cut. Everything else works like standard HDD, just with the kit and the time that rock demands.
Best for: Steered crossings where the ground is sandstone, limestone or other hard rock.
Read more →Directional drilling used to install gravity drainage and sewers to an exact fall, without digging a deep trench. Steered drilling can hold the precise gradient a drain needs, which is why it can replace far slower and costlier deep-dig or tunnelling on the right scheme.
Best for: Deep or large-diameter gravity drainage that has to run to a set fall.
Read more →A rotating auger inside a steel casing is jacked forward from a launch pit, carrying the spoil back as it advances. It is a pit-launched, jacked method rather than a steered one. We can arrange it, though on cost most clients end up drilling the same crossing instead.
Best for: Straight, level casing crossings under a road or railway in stable ground.
Read more →Large pipes are pushed through the ground from a thrust pit by hydraulic jacks, one length at a time, often with people working at the face. It comes into its own at the large, man-entry diameters that drilling cannot reach, but it is heavy, slow and shaft-hungry on smaller crossings.
Best for: Large structural or man-entry sewers and culverts.
Read more →A remotely controlled tunnelling machine is jacked forward while holding a very tight line and level, even below the water table. It is the precise, expensive end of trenchless, and earns its cost on large gravity sewers that have to be exact over a long run.
Best for: Large, precise gravity sewers in difficult or water-bearing ground.
Read more →Four things decide it, and you do not need to know them all before you call us:
The honest shortcut is to send us the job. Tell us roughly the pipe size, the distance, the location and what you know about the ground, and we will tell you which method fits, what it is likely to cost, and whether another approach, including just digging it, would serve you better.
Questions answered
Trenchless means installing or replacing an underground pipe, duct or cable without digging an open trench along its whole length. Instead of excavating the full route, a trenchless method bores or drives the pipe underground from small pits at each end, so the ground, surface and anything on it are left largely undisturbed. Directional drilling, impact moling, pipe ramming and auger boring are all trenchless methods.
Often, yes, once you count the whole job. Open-cut digging can look cheaper per metre until you add deep excavation, reinstating the surface, traffic management, the disruption to a road, railway or watercourse, and the time it all takes. A trenchless crossing installs the pipe in one bore with two small pits, so on deep, busy or sensitive crossings it is frequently cheaper overall and far less disruptive. On one 900mm drainage scheme, drilling instead of tunnelling saved the client around £1 million.
It comes down to the pipe size, the distance, the ground and how precise the line and level have to be. As a rough guide, a short, small service run suits impact moling; most steered crossings of a road, river or railway suit directional drilling; larger steel casings suit pipe ramming; and big, precise gravity sewers may need pipe jacking or micro tunnelling. You do not have to work it out yourself. Send us the details and we will tell you honestly which method fits, including where simply digging a trench would serve you better.
Both install a pipe without a trench, but they work differently. Impact moling fires an unguided pneumatic mole through soft soil over a short distance, with the aim set at launch, so it is cheap and quick but cannot be steered. Directional drilling uses a steerable drill head tracked by a survey system, so it can follow a planned path, go further, handle larger pipes and stay accurate. Moling suits short service runs; drilling suits everything beyond that.
Most can, but not all. The size of the pipe, the ground conditions, the depth and the required accuracy all decide whether a trenchless method works and which one. Small services, utility ducts, water and gas mains, large-diameter product pipe and gravity drainage are all routinely installed trenchless. Where the diameter, the ground or the tolerances rule drilling out, jacked methods like pipe jacking or micro tunnelling take over. We will always tell you straight if open-cut is genuinely the better answer for your job.
Keep reading
A closer look at the variations of directional drilling, by rig size, ground and purpose.
Read →Walkover, wireline and gyro guidance, and why motorways and rivers are tracked differently to minor roads.
Read →An honest guide to what trenchless crossings cost and what moves the price.
Read →Tell us the pipe size, the distance and the location, with any drawings you have, and we'll tell you straight which trenchless method fits and what it should cost. Free, no obligation.