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Hole punching the M25

A drill rig that was designed, built and delivered in just two weeks has helped widen a major structure on the M25. NCE reports.

One of the first major structures to be widened on the massive £6.2bn M25 widening project is the seven span Berry Lane Viaduct, just south of junction 18 at Rickmansworth in Hertfordshire.

The Skanska/Balfour Beatty partnership that is carrying out the work is widening each side of the 260m long structure by casting new reinforced concrete pier heads alongside those supporting the existing structure, with a new pair of vertical columns supporting each pier head.

Three, 24m long precast concrete beams sit alongside each other, spanning between the new pier heads, and a new section of bridge deck is then cast on top of the beams.

“I sat down with Castellan and told them what we needed, and within two weeks the drill had been built ”

Andrew Willcock

The new sections of pier head and deck are bonded to the existing viaduct using steel tie bars glued with epoxy grout into holes drilled into the structure’s concrete − a process that requires hundreds of holes to be drilled at varying depths and diameters.

The drilling is being carried out by specialist contractor AJ Willcock Holeformers, which turned to US drill rig manufacturer E-Z Drill and its European concessionaire Castellan Group to design and build a drill specifically for the project.

The result is the E-Z Drill 210B-42DD, a compact, wheelmounted pneumatic drill that uses a compressed air powered Consolidated Pneumatic CP32 rock drill mounted in an extended frame that increases the rig stroke from 450mm to 1.05m.

An air motor with an automatic brake controls the chain drive drill feed system, and the whole rig is powered by a 5.6m³/ min, 690kN/m² compressor.

The M25 drill rig

The M25 drill rig

The drilling operatives work from scaffold platforms, using a combination of 1.2m and 2.4m long extension drill rods with the new machine to drill 32mm, 40mm and 57mm diameter holes to depths of between 750mm and 2.85m into the existing reinforced concrete.

The rig can be adjusted to accommodate the different height of the holes from the working platform, and has been designed to move quickly and easily from one hole to the next.

“I sat down with Castellan and told them what we needed, and within two weeks the drill had been built and shipped from E-Z Drill in the US and was on site drilling holes,” says AJ Willcock proprietor Andrew Willcock.
“It’s the only one of its type in the UK and is doing a great job. There is no risk of any hand arm vibration being transferred to the operator, who can use it all day long.”

AJ Willcock completed drilling on the side of the viaduct that carries the clockwise carriageway in November and has now moved onto the viaduct’s anticlockwise carriageway. As soon as the drilling was completed on the clockwise side, Skanska/Balfour Beatty moved in to fix and glue the tie bars into the existing pier heads and bridge deck, and then to build the new structure to support the widened carriageway.

Working onsite at the M25

Working onsite at the M25

In addition to the special rig for the Berry Lane Viaduct, AJ Willcock has also bought two standard E-Z Drill rigs for use on widening the pavement of the M25 between junctions 16 and 19 and junctions 27 and 28. These rigs are drilling more than 80,000 holes, up to 300mm long, horizontally into the exposed vertical edges of the pavement slab. The holes are used for 20mm diameter tie bars that are used to key into new sections of concrete carriageway.

The M25 is being widened as part of a project being designed, built, financed, operated and maintained for the Highways Agency under a 30-year concession by Connect Plus, a consortium of Skanska, Balfour Beatty, Atkins and Egis Projects. The project also involves the Skanska/Balfour Beatty joint venture widening of the M25 between junctions 27 and 30 and refurbishing the A1(M) Hatfield Tunnel.

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