There is no question that HS2 is an ambitious project. Connecting London to Birmingham, Manchester and Leeds, the line will enable trains to reach speeds of up to 250mph and would run as often as 14 times an hour in each direction. With the Department for Transport stating it will triple the capacity of trains across the entire route, the infrastructure for this high-speed rail network is a huge undertaking. The first construction phase alone, from the West Midlands to London, will include over 50 viaducts, 110 embankments, 150 bridges and 32 miles of tunnels.
The temporary works industry, covering formwork, shoring and groundworks, will play a vital role in delivering this project and meeting these challenges. But what kind of considerations will influence the best kind of temporary works system for each type of structure, and how can these contribute to the safe, timely and cost-effective delivery of a project like the UK’s high-speed rail network?
Bridging the gap
Although it may appear obvious when it comes to bridge construction, a thorough understanding of every element – from the type of bridge and its location to its height, length and the timescales that need to be adhered to – is key to ensuring the right formwork and shoring solution can be engineered. A temporary vehicle bridge may only require a standard ‘off-the-shelf’ solution, such as a quick bridge, bailey bridge or panel bridge, whereas a permanent bridge spanning a live rail line may demand a bespoke temporary works solution to form the finished structure. Integral debris protection will be required too, to ensure the safety of passing trains below.
Terrain and wind speeds also have an impact. If ground conditions are poor or unstable, or if there’s a likelihood that adverse weather will affect the ground over the construction cycle, then additional support for a shoring structure may be required. This might include trusses that span between pier foundations, or a formwork solution that’s suspended from the permanent works steel of concrete beams spanning between piers. Similarly, high wind speeds may influence crane usage and installation methods.
For permanent bridges that might include multiple piers, which typically run over live roads or railways, a composite construction method is often best. Safe and fast to construct, horizontal steel or concrete beams are seated on bearings, which are positioned on abutments and piers and stitched together, before providing support to temporary or permanent works solutions forming the deck between the deck edge’s cantilevers and parapets.
Alternatively, there’s cast in-situ bridges, which are generally more complex and sometimes unusually shaped. Casting in-situ is often the preferred method of construction for balanced cantilever and cable-stayed bridges, as well as large viaducts.
Some projects may specify pre-cast segmental box girder bridge decks. These tend to be used for long viaducts and high-speed railway bridges, with spans of between 20 and 50 metres in length and are assembled using a launching gantry traveller. With the pre-cast units fabricated off-site and delivered in modules, space and crane usage are two key considerations when choosing this method of construction.
Tackling tunnels and viaducts
Tunnel construction will depend on the ground and groundwater conditions, the length, diameter, depth and shape of the tunnel, as well as the need to make sure the tunnel excavation is a safe and efficient working environment.
When considering formwork and shoring, the shape of the structure and the method of construction will determine the type of temporary works solution, such as whether the tunnel has a flat or curved soffit, or whether it is a cut-and-cover or bored tunnel. For short tunnels – passing beneath a rail embankment, for example – a standard temporary works system will often be sufficient. One that extends for several miles will require a more bespoke solution.
Another consideration is whether the entire tunnel is to be cast in one section, or are the slab, walls and roof to be cast separately? Innovative solutions such as a hydraulic casting system on castor wheels, whereby, once the concrete is cured, then the system can be struck and moved onto the next pour, can make a big difference in meeting tight deadlines and ambitious construction cycles.
RMD Kwikform supported the £49 million Stockley Viaduct Interchange at Hillingdon, part of the Crossrail project. A bespoke shuttle traveller system to support the viaduct’s construction was engineered, which had to accommodate four live railway lines running adjacent to the site and in close proximity to the walls that were being formed. To ensure the solution could accommodate the limited space between the track and traveller system, RMD Kwikform used Master Series, a frame analysis programme to analyse the pressures from passing trains on the shutter and determine whether the design of the traveller system was fit for purpose.
Large-scale rail infrastructure projects, such as HS2, require temporary works systems that are innovative, robust, and can meet tight deadlines. Depending on all the elements of a build, the right solution can be determined to meet the client’s exact needs.
For more information, please visit www.rmdkwikform.com