HCE Bridges

Project Name: HCE or Hidden Critical Elements

Scope

TRS have secured a package of 28no steel structures across the South West Region with the plan to install FRP (Fibreglass Reinforced Plastic) ballast retention panels onto the face of the steel girders.  The purpose of the scheme is to allow NWR and its designer to inspect what they call the hidden critical elements.  These are in fact the steel deck sections which get congested with small ballast, grit and water and can in turn corrode and cause decay to the structure at it critical points.  In the future endoscopes will be used to inspect these HCE areas via grating in the FRP or designated inspection hatches. 

Difficulties

Quite a lot of the structures have very high ballast (up to 900mm) with as little as 100mm clearance from the sleeper end to the face of the girders, this meant that installation was going to be tricky.   The bridge spans vary from 9m to 70m and depending on how may girders there are there could be as much as 240m of ballast retention to be installed on any one bridge.  With possession times at a minimum, the initial concern was how were we going to excavate the ballast quickly and efficiently leaving enough time to install the FRP, its components, as well as having enough time to get the ballast back in and fit for the passage of trains.  After lots of research the tube cube (which essentially is a large hoover) was deemed as the right piece of equipment due to its capability of sucking approx 1.2t of ballast quickly. 

Outcome

Having just completed a 9 day blockade on the North Devon Line, TRS have managed to install approx 400m of FRP ballast retention over 5no structures.  The tube cube was very efficient and made the excavation of ballast a relatively easy operation.  We were achieving 10m per hour of ballast excavation at 800mm depth.  This just could not be achieved with the traditional manpower and shovels due to the constraints on site.  The tube cube has reduced our programme hugely, leaving our skilled labour to install the FRP retention in record time.  The design of the tube cube also means that we are able to instate the ballast but lowering the tube cube over the excavation and opening the hatch doors on the bottom, thus again saving on valuable time and labour costs.