Timber headings – the unseen technical challenges
While many of our clients will be familiar with the broad range of services we provide as an experienced team of consulting engineers, there are aspects of our work that are more niche and don’t receive the same attention, despite their usefulness.
A recent news article about the death at the age of 99 of Squadron Leader Richard Churchill, a survivor of the Great Escape and one of the 76 prisoners who crawled through tunnels to escape Stalag Luft III, reminded of one such practice, timber headings.
Anyone who has seen the film will know what a timber heading tunnel looks like and indeed the construction method, which still typically involves miners tunnelling by hand.
Timber headings remain a traditional and versatile method of tunnel construction that is crucial to the success of many projects, large and small, simple or complex.
While designing underground tunnels may seem relatively straightforward in comparison to some of the eye-catching above ground temporary works we design and check, they require a lot of important calculations and detailed design-work.
Rather than being manufactured with heavy machinery, timber headings are constructed by hand, typically by miners using hand tools in dark, cramped conditions, which automatically increases the difficulty and risk involved.
Timber headings are a cost-effective solution for the installation of drainage connections or other services where access is only possible under an existing structure or highway, with trenchless construction or micro-tunnelling not a viable option.
The more complex the project, the more important it is for contractors to recruit the design expertise of consulting engineers like PDMA, who have been designing timber headings for decades.
Projects requiring timber headings all start with a thorough survey of the site and its surroundings, making the necessary measurements and calculations.
This involves inspecting the ground conditions, testing the soil and making a judgement on the size and scale of timber needed to construct appropriate headings, able to support the calculated loads associated with deep tunnelling.
Detailing the headings for constructability and carefully assessing the imposed loads, is critical, as it allows us to design tunnels that will not be compromised structurally, with miners working in them often many metres below the surface.
Once we have a detailed picture of the surrounding area and likely conditions, we can then tailor the headings to withstand and overcome any challenges peculiar to the site.
More than meets the eye
Once the tunnels have reached their target, typically a main sewer away from the site, a connection is made and then the tunnel is back-filled, usually with concrete, to guarantee future stability. Having done their job, the timbers are left in place to offer support as the tunnel is completed.
Under the ground, out of sight and out of mind, these engineering mini-miracles that have been around for thousands of years, can be easily forgotten, yet their importance should not be underestimated. Especially if you need to connect the sewer from your housing development to a main sewer under a major highway close by.
Through a combination of careful calculations and detailed measurements, PDMA will continue providing a first-class service to contractors who require assistance designing timber headings that get the services where they need to go and keep the miners tunnelling in safety.