HS2 and working platforms for plant
For those of us in the construction industry, it is good news that the Government has now confirmed that the first Phases of HS2, from London to the Midlands will now go ahead.
Enabling works have continued to be undertaken over the last few years, perhaps demonstrating a confidence in the scheme getting the green light that few in politics seemed to share.
The project will keep the industry busy for the foreseeable future and will require the construction of many working platforms throughout the length of the route, as construction will start in many locations at once – this is not a linear process following the route out of the capital.
Accessing sites safely
According to the BSI’s PAS8812 Temporary works – Application of European Standards in design – Guide, working platforms are temporary structures comprising layers of fill or other materials placed on existing ground that provide a foundation for heavy construction plant.
PAS8812 refers to BRE report 470 for guidance on the design and construction of working platforms. However, the method in BRE 470 does not work well when partial factors are applied to soil strength and loads as required by BS EN 1997-1:2004+A1:2013 Eurocode 7. Geotechnical design. General rules (Eurocode 7).
The Temporary Works Forum (TWf) recognised this and formed a committee to investigate how working platforms could be designed in accordance with Eurocodes and still be economical. I was personally heavily involved with the committee and it took over five years work to complete guidance that was generally acceptable to all at the TWf.
The resultant document, TWf2019:02 Working Platforms – Design of granular working platforms for construction plant: A guide to good practice was published in April 2019 and is freely available via the TWf website.
Compared to the BRE470 method, the TWf method requires more design effort, something we have found with most Eurocode design requirements. In some cases, it will provide a more economical platform design than the BRE method which was one of the desired outcomes of the guide.
I had mixed feelings awaiting The European Federation of Foundations Contractors and the Deep Foundations Institute (EFFC/DFI) Guide to Working Platforms which was published recently.
Temporary Works Forum leading the way
On the one hand, I wanted to see the latest guidance but it would have been disappointing if all the work done by the TWf was superseded so soon after its publication. The EFFC/DCI publication is very much a review of methods used around the world.
We did a similar review at the TWf and found several methods for the design of a stronger material overlying a weaker material and the method adopted in TWf2019:02 was by far the best method we found when used with Eurocode 7.
The EFFC/DCI publication concluded that the BRE470 method was the most widely used method and is used in the USA, Canada and in a modified form in France.
Recently, Lees has published a method of design in Ground Engineering magazine which has promise with reinforced platforms but is uneconomic for the design of unreinforced platforms when the partial factors from Eurocode 7 are applied.
Other than these three methods, the EFFC/DCI do not refer to any other method of design. I am pleased that the method published by the TWf, that we all put so much effort into, is still regarded as the state-of-the-art solution and will be the method in use for the design of the many platforms required for HS2 and other similar projects.
The Midlands will witness the construction of many such working platforms, given the amount of engineering and construction required to traverse the area and arrive successfully at Curzon Street Station in the heart of Birmingham.
For more details about the expertise we offer in the design of working platforms, please get in touch with me directly firstname.lastname@example.org or the team here at PDMA on 0808 196 1460.