Under-Track crossing installations at Weston-Super-Mare

About the project

Enable Infrastructure (formerly BCM Construction) were tasked by Western Power Distribution (WPD) with installing under-track crossings (UTX) for new cables in Weston-super-Mare. The project had to be completed while the railway remained fully operational throughout.

The cables were to connect the feeder grid to two separate substations, one at Warne Road and the other at the North Somerset town’s Bourneville Road playing fields. Since these locations lie outside Network Rail’s fences, the necessary thrust and reception pits for auger-boring had to be positioned on third party-owned land. (WPD had obtained the necessary third-party consent before the UTX installation work began).

Because Enable Infrastructure were auguring under an operational railway, track monitoring had to be undertaken continuously throughout the project. The programme also involved working within live WPD substations.

To ensure we adhered to the programme, we broke this complex project down into itscomponent assets, which enabled us to concentrate on delivering manageable scopes of work.

A further key to its successful delivery was effective collaboration, both internally and externally. Within the Enable Group, Enable Infrastructure’s civils team and Enable Power Systems team worked closely with Enable Design (formerly Equate Design). Our effective stakeholder management plan helped resolve the differing demands of WPD and Network Rail.

“Enable Infrastructure worked to the high standards set by WPD. Despite on-site challenges, they met the deadlines given to them, sticking to their programme of works. The works were completed safely and on time. I would have no hesitation in using Enable Infrastructure in the future.”
Gary Beasley, Western Power Distribution project engineer

Once the shaft pit locations were marked out by our setting engineer in accordance with AFC (approved for construction) design and the permit granted, the excavation began. We used a dig-and-push method to create a 3.4m-deep drive pit (4m x 4m) and a 2m x 2m reception pit, also 3.4m deep.

Reinforced concrete (RC) thrust walls were constructed in the drive pits for the guided auger-boring equipment, with two sides 300mm thick and the other two 500mm thick. We constructed formwork walls with shuttering ply, timbers, and reinforcement A393 mesh.

After the concrete had been poured into the formwork, the walls were tested to confirm that the RC pit walls had achieved the correct strength in line with the design.

Once Enable Design engineers had confirmed the set-out and mark line gradient of the bore, and the permit to drill had been signed, we commenced the auguring process.

We used a sacrificial steel sleeve, with additional sections connected by welding. A 13t machine was used to load the sleeve, flight auger and cutting head; they were lowered under the supervision of a qualified slinger signaller and banksman. The cutting head was connected to the rear of the pilot rod, and the flight auger connected to the drive of the auger machine. Boring then began, with the auger being filled.

The sacrificial steel sleeve was pushed into the ground, whilst simultaneously the flight augers were rotated. They were then retracted to the drive shaft, clearing any loose spoil that remained inside the sleeve. As each section of flight auger arrived in the drive shaft, it was disconnected and lifted to the surface.

The spoil from the augers was discharged into the drive shaft, loaded into skips and removed from the pits with the 13t machine. The spoil removed was closely monitored to assess how closely it corresponded to the volume of the sleeve installed, with the expected increase being around 15-20%, after allowing for bulking.

On completion of auger-boring, the auger machine master frame and ancillary items were removed from the shaft using the 13t crane.

The challenge

• A working environment that was within a park, on a football pitch and adjacent to drainage rhynes. There was the specific challenge of protected trees within the route protection zone (on the playing field near the drive pit), which necessitated meticulous measures to ensure we kept within environmental regulations
• The sometimes-conflicting requirements of WPD and Network Rail, especially those arising from the requirement for us to keep the railway operational and, at the same time, to work within live substations.

The solution

In preparation for the contract, we drew up a comprehensive Environmental Management Plan, which included agreeing with the local authority a strategy and plan to protect the trees. This involved establishing and implementing exclusion zones to protect the trees, alongside a route protection plan.

To solve the second challenge, we first facilitated open dialogue between all parties to ensure there was a clear understanding of what was required. Once this had been established, our experienced Enable Design team devised a plan that suited all parties.

The deliverables

• Two under-track crossings
• 610mm sleeve auger
• Two 2m x 2m x 3.4m reception pits
• Two 4m x 4m x 3.4m drive (thrust) pits
• Reinforced concrete retaining walls
• Reinforced concrete floors
• Temporary works
• Sheet piles
• Formwork
• Resurfacing – Tarmac/concrete
• White-lining
• Reinstatement of a play park and football pitch
• Installation of UTX signage
• Ducts: 4 x 150mm & 3 x 100mm
• Steel casings (32m at Bourneville & 28m at Warne Rd)