Ask any drilling crew what makes a crossing go well or badly, and they will nearly always say the same thing. It is how well we knew the ground before we started. A directional drill is a controlled operation, but only as good as the information behind it. Good ground investigation turns a bore from a gamble into a planned job.
What the ground decides
Almost every important decision about a crossing follows from the ground:
- The method. Soft ground, mixed fill and solid rock each call for a different approach. Rock, for example, we drill with a mechanical cutting system built for hard ground rather than a fluid-hungry mud motor. You cannot choose the right method well without knowing what you are drilling through.
- The bore profile. The line and level of the bore, the depth of cover, and the curve radius all depend on the ground conditions along the route.
- The tooling. The bit, the reamer and the fluid programme are all matched to the ground. Knowing there is rock, or cobbles, or a soft layer, before mobilising means arriving with the right kit.
- The risk of surprises. The classic bad day is hitting something the survey did not show, such as an old foundation, a band of rock or an obstruction. Good ground investigation is how you avoid it.
Ground investigation and asset-owner approval go together
On a road, rail or watercourse crossing the ground information does more than guide the drill. It feeds the approval the asset owner or regulator requires. Highways crossings are designed and monitored for settlement under CD 622, rail crossings under Network Rail’s UTX approval, and river and watercourse crossings under the Environment Agency’s flood risk approval, where the depth below the bed matters as much as the line. Each of these rests on knowing the ground, so the effect of the bore can be assessed, certified before construction where required, and checked against a baseline. Without the ground data, that design cannot be done properly.
Why it pays for itself
Ground investigation can feel like a cost you would rather skip, especially on a smaller job. But the sums usually favour doing it. A bore planned on good ground data goes in cleanly, with the right tooling, first time. A bore planned on guesswork is the one that stalls, needs a change of method partway through, or damages something above the line. The investigation almost always costs less than the day you lose without it.
And it does not have to be expensive. Ground investigation does not always mean a geotechnical company sinking boreholes, taking samples and writing a thousand-page report. Often a couple of trial pits dug by the groundworks contractor already on site tells us a great deal, such as what the made ground is, where the water sits, and whether we are into clay or rock. The scale of the investigation should match the size of the project. A short service crossing might need no more than those trial pits and the records that already exist, while a long crossing under a major river or motorway justifies proper boreholes and testing. The point is to match the level of investigation to the risk, which is exactly what a good feasibility appraisal does.
How we work with it
We interpret ground information for the crossing, not just collect it, and we can arrange the ground investigation where a job needs deeper data. We build it into the design and CAD work so the bore profile, the tooling and the settlement design all rest on the same picture of the ground. And with every quote we give a free feasibility view so you know early whether the ground makes your crossing straightforward or something to plan around.
If you have a crossing coming up, send us whatever ground information you already have. We will tell you what it means for the bore, and whether it is enough to drill on with confidence.