Awards, contracts & appointments

13.11.07

Avoiding the trap

For decades, the insertion of site workers hands inside the splices of heavy suspended rebar pile cages for the fitment of U bolts (“bulldogs”) has been common practice. Whilst the lower rebar cage may be securely attached to the pile casing, the upper cage being held by a service crane has the potential to slip and injure the worker.

So the invention of a simple, robust device, integral with the prefabricated cages, which replaces U-bolts and avoids the need to place hands in harms way has been positively welcomed on a number of prestigious civils projects.

Pile reinforcement specialist Romtech’s Safe-Splice product significantly reduces the traditional hazards of a manually splicing too vertically overlapping rebar cages by removing the U-bolts altogether. If U-bolts are used to fasten the respective longitudinal rebars together then workers must insert their hands inside the cages to fit the bolt shank, saddle and nuts prior to torquing these up. The intrinsic risk of this system is the trapping of hands or fingers if the top cage is inadvertently lowered.

The origin of the bulldog grip is the wire rope industry in which the relatively soft wire rope can be spliced by the use of multiple grips which squeeze filaments together. Rebar by contrast is very hard and irregular in section so the use of bulldogs in rebar splices works by generating a less-than positive friction grip as the rebar elements are forced together. This results in many bulldogs being used on a splice between two heavy cages which means that multiple opportunities for hand-trapping exist within a single pile.

“The current, intensive site safety culture has created a back-drop which has helped to identify just how risky the insertion of hands inside pile cages can be,” explains Romtech technical director Steve Render.

“This has demonstrated the need for a complete change of approach, with particular project management teams wanting to avoid the risk. Since most rotary piling contracts use an off-site factory produced cage solution, we sought to develop a patentable, hands-free product which could be built into our cages at the works. Safe-Splice was the result.”

In comparison with the use of U-bolts, the Safe-Splice system allows site workers to stand a metre or so away from the edge of the pile casing. Three or more sets of plates are factory, fillet – welded (to UK CARES specification) to the bottom of certain rebars in the top cage. These plates have been female – threaded with heavy bolts fitted. The lower cage has a band welded to the rebars just above the trapping off point. After the cages have been ‘offered up’ over the pile casing, workers only have to use an extended wrench to drive the bolts into the band and so create a massive structural connection between the two cages. Hands are laid on only the wrenches, not on or inside the cages. In effect, bolts enter the rebar cages instead of workers hands.

Safe-Splice was used on abutment, wing-wall and pier piles to the new replacement overbridges on Balfour Beatty / Skanska JV’s M1 widening project at Hemel Hempstead. Currently it is being utilised in 2000t of Romtech’s pile cages for a £500m retail and office development at One New Change in London’s square mile. Cementation, acting for main contractor McGee are using Safe-Splice for wall and bearing piles on this prestigious project.

The widening of the M6 motorway between Carlisle and Guards Mill on the Scottish border incorporated Safe-Splice in massive prefab B50 mm rebar pile cages for the foundations to the heavily skewed bridge carrying the new carriageway over the main West Coast Main line. The Carillion Piling project team saw Safe-Splice both as a means of raising the threshold of site safety and as a means of boosting site productivity.

Where the rotary – bored piling technique is used on rail projects, the short rebar cage sections demanded by a limit on the ‘fall radius’ or on headroom imply more cage to cage joints per pile. This tends to create a greater potential for hand trapping with traditional U-bolted joints. The Safe-Splice product therefore offers a greater benefit of terms of risk limitation in this burgeoning market sector.

Tell us what you think – have your say below, or email us directly at opinion@railtechnologymagazine.com

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