Communication Duct Installation Under the M1, Junction 15, Northampton

Who we worked for

MSF Mason Street Furniture is a Northamptonshire highways contractor. They work across street lighting, traffic signs, EV charging and civil engineering, and operate as an Independent Connections Provider. MSF engaged EPS for the two slip road crossings. Winvic, one of the UK’s largest industrial and logistics contractors, was delivering the wider scheme for Segro.

Both needed the same thing: communications duct across two live M1 slip roads, without opening the carriageway. Excavating a motorway slip road means full closure, diversion routes and reinstatement to National Highways specification — on one of the busiest stretches of motorway in the Midlands. EPS came in as the duct installation contractors for the two crossings where that could be avoided.

What made this crossing difficult

Two things made this job difficult, and both came down to time.

The working window. Each possession ran eight hours, but only six of those were on the road: nine at night until three in the morning, with an hour either side for getting set up and getting clear. Six hours to launch, drill a 50-metre bore, ream it, pull the duct through and clear the site. There is no overrunning on a motorway slip road. The possession ends when it ends, and if the bore is not finished the site is made safe and the road handed back regardless.

Everyone else. Ours was not the only work happening at Junction 15 on those nights. Several contractors were operating in and around the same area, sharing access and working space inside the same narrow window — so the programme had to be coordinated around other crews before a single metre could be drilled.

On top of the clock: a live motorway environment with the safety regime that comes with it, existing services in the verge and central reservation, and duct that had to arrive on line and at depth first time, because there was no opportunity for a second attempt.

How we did it

Drilling to a design, not to a plan of our own

On a crossing beneath the strategic road network, the bore profile is not the driller’s to invent. Winvic and their designers produced the GPR utility data and the drill profile, and carried the geotechnical design duty that sits with the designer under CD 622. The ducting layout was designed by BWB Consulting as part of Works 11, with the drawings specifying which ducts were to be installed by trenchless methods.

One thing the design deliberately left to the contractor was the exact crossing location. That is not a loose end. It is the point at which drilling experience has to meet the drawing. EPS confirmed the setback each rig needed and checked the profile would work from the positions available, before anything was committed to. Getting that wrong is discovered at two in the morning, with no room to move the rig and no possession left. EPS was engaged to execute that design and to prove it had been executed.

That distinction matters more than it sounds. A contractor who improvises a bore path beneath a motorway has nothing to submit afterwards. A contractor who drills to an approved profile, and logs it, has a record that stands up.

What CD 622 requires

CD 622 Managing Geotechnical Risk is the National Highways standard governing geotechnical risk on the strategic road network. It absorbed HA 120/08, the former standard covering trenchless installation of services beneath motorways and trunk roads, so a duct crossing under an M1 slip road falls squarely inside it. These works were carried out to Revision 1, dated March 2020, which was the version in force at the time. A further version was published in September 2025 — anyone planning a crossing now should check which revision applies to their scheme.

In practice a crossing is not simply approved and drilled. The design carries defined geotechnical duties, the works are documented against that design, and the record is what demonstrates the highway asset was not put at risk. All of it happens before the possession. None of it can be resolved on the night.

Drilling and pull-back

Both crossings were drilled with a Ditch Witch JT3020. Each location took two 50-metre shots, side by side, from pits sited outside the running lanes — four bores in all, each one pilot-drilled, reamed out to 160mm and pulled back with a single 125mm duct inside the same possession.

That is one duct per bore, not two ducts sharing one. The two are not interchangeable: a pair of 125mm ducts bundled together sits inside an envelope around 250mm across, so sharing a bore means reaming to roughly twice the area rather than pulling a second 160mm shot beside the first.

Two separate locations meant the whole sequence — set-up, pilot bore, ream, pull-back, make safe — run from scratch at the second. Nothing carried over from the first except what the crew had learned.

How do you prove a bore was drilled to the approved design?

Every bore was logged as it was drilled. On this job that was a Subsite Marksman locator — the same manufacturer as the rig, both Ditch Witch. The locator guiding the head also reads depth and pitch at every rod, so the as-built profile is built up while the bore advances rather than reconstructed afterwards.

That log is the evidence. It shows the bore that was drilled against the bore that was designed, and it is finished by the time the crew leaves site. Where the design duty sits with the client’s designers, handing back a verified as-built is what closes the loop.

Road monitoring was set up independently by others across both crossings. All readings came back within tolerance — no measurable movement in the carriageway above any of the four bores.

What ground conditions are found at M1 Junction 15?

The ground here is documented properly, which is not always the case on a highway crossing. A factual ground investigation report was produced by Hydrock Consultants for Segro under DCO Workstage 8, and three of its rotary-cored boreholes — HYD-RC-1001, 1002 and 1002a — were sunk specifically for the northbound on-slip and service crossing. Two more, HYD-RC-1005 and 1006, targeted deep elements including the service crossing. That is site-specific data at the crossings themselves, not a map extrapolation.

Borehole 1002 has a footnote worth repeating, because it says something about how tightly this scheme was controlled: it was abandoned at 6.80 metres when a badger sett was found nearby, backfilled with bentonite pellets, and redrilled as 1002a only after ecologists had relocated the badgers. That is why there are two logs at almost the same coordinates.

The sequence beneath M1 Junction 15 runs:

Stratum	Depth to top (m bgl)	Thickness (m)
Topsoil / Made Ground	0.00	0.16 to >1.20
Glaciofluvial Deposits	0.16 – 0.70	1.00 – 14.10 (avg 3.96)
Oadby Member (Glacial Till)	0.60 – 6.70	2.20 – 13.60 (avg 6.21)
Whitby Mudstone Formation	7.00 – 17.60	Not proven

Both are BGS-recognised units, and the sequence is what the regional mapping would predict for this part of Northamptonshire: Anglian-age glacial till and glaciofluvial outwash over Lower Jurassic Lias Group mudstone.

What that means for a bore. A crossing at highway depth sits in the superficial deposits — glacial till, glaciofluvial material, or the boundary between them — rather than in bedrock. The Oadby Member is recorded as firm to stiff slightly sandy, slightly gravelly clay, which is cohesive, holds a bore open and steers predictably. That is the ground a driller wants.

The risks sit in the detail. The till carries sand lenses and occasional cobbles, with gravel of flint, chalk and sandstone — cobbles being the classic cause of steering deflection and a compromised bore. Selenite crystals up to coarse gravel size were logged from around 2 to 3 metres, occasionally with cobble-sized gypsum. And the glaciofluvial deposits come in two forms: a fine, clay-dominated material that behaves much like the till, and a coarse sand-and-gravel variant that does not — running sand and loss of circulation are live risks where a bore clips it. Groundwater in the Oadby Member was recorded between 3.90m and 15.50m below ground level, though the report notes water flush in the rotary-cored holes masked groundwater during drilling, so those figures are a guide rather than a water table.

What we encountered. The crew logged clay throughout, consistent with the till and the fine glaciofluvial material rather than the coarse variant. No obstruction was met on either crossing — which matches the investigation, where no significant obstructions were recorded either. The ground behaved as the report said it would, and on a six-hour possession with no second attempt available, that is the difference between a routine night and a very long one.

What went wrong

Nothing did — and that is worth saying plainly rather than dressing up.

All four bores were drilled, reamed, pulled and cleared with time in hand, two to a possession. Neither possession ran over. No obstruction was met. The monitoring came back in tolerance. On a live motorway slip road, that is the outcome everyone wants and nobody should assume.

It was not luck. The ground had been properly investigated, with boreholes sunk at the crossing locations themselves rather than nearby. The profile was designed and approved before anyone booked a possession. The rig setback was checked against the positions actually available, so the crew were not solving a geometry problem in the dark. And the bore was logged as it was drilled, so the evidence was complete before the site was handed back.

The work that keeps a six-hour possession comfortable happens weeks earlier. When a motorway crossing overruns, the cause is almost never the drilling.

Handback

The pits sat clear of the running surface, and pit excavation and reinstatement were carried out by others. EPS’s part was the bore: drilled, logged and complete inside the window, so nothing held up the handback. Off the road by three, as agreed.

Why directional drilling rather than open-cut

	Open-cut trench	Directional drilling
Slip road surface	Excavated across full width	Never broken
Possession required	Extended, likely multiple nights or full closure per location	One night possession per location — six hours on the road
Diversion routes	Required	Not required
Carriageway reinstatement	Full National Highways specification	None — no carriageway was opened
Verification	Reinstatement inspected after the fact	As-built logged during the bore; monitoring confirmed no movement
Handback risk	Trench open at shift end	Site safe at shift end
Disruption to motorway traffic	Significant	None to the running carriageway

On a motorway slip road, the deciding factor is not cost per metre. It is whether the road can be handed back when the possession ends.

That is why this was directional drilling work. The length suited it, the accuracy demanded it, and there was no second attempt available.

The outcome

Both crossings were completed inside their possession windows, on two separate nights. That was the constraint governing everything about this job, and it was met twice.

All four 125mm ducts went in on line and at depth, drilled to the approved profile and logged as they went. The carriageway was never opened. Independent monitoring recorded no movement above any of the bores.