Ever since humans began mining the earth we have lived with the horror of being buried alive by collapsing ground. And despite strict health & safety regulations, construction workers still suffer injury and death in unsafe excavations.
In the UK, two main techniques are used to secure trenches and pits, keeping workers within them safe. Sheet piling can be used, or box shoring. Sheet piling is flexible, but requires the use of a piling rig. Box shoring is lifted into place as an assembled unit but can require excavating under the edges of the box, and can lack flexibility.
Slide rail systems offer an alternative. They are assembled from beams, rails and spacers, with the shoring itself slid in from above, all using the same excavator that is used to the dig the trench itself.
These systems are modular, making them easy to adapt to excavations of different shapes and sizes. They have been widely adopted in Germany and the Benelux countries and have been accepted in many other markets. But, so far, they have struggled to make a mark in the UK.
In 1949, Germany had reaped the whirlwind. Its cities had been bombed to the foundations, and millions of men had been killed. Josef Emunds and G眉nter Staudinger saw an opportunity to help rebuild, and to build a business.
鈥淓verything had been destroyed,鈥� says Sven Radem盲chers, international development manager for Terra Infrastructure, the successor to the company the two men founded. 鈥淔or the men that survived the war it would be an absolutely no-go building up everything again 鈥� you survived the war and then be killed because of a trench collapse.鈥�
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Emunds and Staudinger started working on mining safety, developing steel shoring systems, before turning their attention to construction, developing the first slide rail system in 1964.
Their company, E+S, went on to build a strong domestic business. One of their top managers was Josef Krings, whose name runs through the development of the slide rail idea like a pipeline through a trench.
With his name on E+S patents, Krings left in the 1970s to start his own business, Krings Verbau, which played a central role in developing a global market for the slide rail concept.
One of the most important deals for Krings was in Saudi Arabia. 鈥淚n Saudi Arabia, it was for pipeline construction,鈥� says Radem盲chers. 鈥淭hey have a lot of sand, the excavation is difficult, so they ordered a lot of trench boxes.
鈥淭hey鈥檇 ordered some Mercedes trucks and sent them to Krings. He loaded them up with trench boxes, hit the road, and drove them to Saudi Arabia.鈥�
By 1986, Krings Verbau was struggling financially and some of its senior staff split off to start their own business, SBH Tiefbautechnik. This company went on to further develop the slide rail, adding safety features including a locking system on the base of the modular panels, which helps keep them secure even when the rails are not perfectly plumb.
Krings returned to stability and continued as an independent business. By 2004, E+S had been bought by steel giant ThyssenKrupp which, later that year, also acquired Krings, bringing the two companies together again.
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A decade later, ThyssenKrupp underwent a restructuring which saw subsidiaries like E+S spun off, in this case to form a new brand,聽 ThyssenKrupp Infrastructure.
Then, in 2022, the business was sold to family-owned private investor FMC Beteiligungs, which also acquired UK equipment company AGD.聽 ThyssenKrupp Infrastructure was subsequently renamed Terra Infrastructure, sitting alongside AGC in FMC鈥檚 construction and real estate portfolio. This spring, AGD announced it would be selling slide rail systems in the UK.
AGD鈥檚 move to bring Terra Infrastructure鈥檚 system to the UK will be a big step forward in the campaign to popularise slide rail systems in the UK. But it is not the first to enter the market.
鈥淚 was working at Mabey Hire in 2016 as sales director,鈥� says Patrick Flannery, 鈥淎nd a chap called Ron Chilton, who I鈥檇 known for 20-odd years, asked me if I wanted to set up National Trench Safety in the UK.鈥�
Chilton, an American, had founded NTS in 2004, along with colleagues from US hire company NES Rentals. The company had built a successful business out of its base in Houston, where the oil industry drove demand for trench shoring. Today, Flannery reckons that NTS is the world鈥檚 biggest company dedicated solely to shoring.
With his success in the US, using slide rail systems from SBH Tiefbautechnik, Chilton was looking for countries with room for growth.
鈥淗e said we need to start in the UK, because there鈥檚 a gap in the market and that gap is slide rail,鈥� recalls Flannery. 鈥淲e hatched a plan to start the company in 2017.鈥�
Bringing a new product into construction can be a challenge. Businesses聽 are conservative about new techniques 鈥� rightly so when there is so much risk involved.
鈥淭he first couple of years were very, very tough, because they didn鈥檛 know the product,鈥� says Flannery. 鈥淚t took years of uphill struggle until we got a foothold in the market.鈥�
Some people are initially intimidated by the product, Flannery says, so he is focusing on educating potential customers.
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鈥淲e show the client how to put it in the ground, and then once they鈥檙e capable and confident and understand the system we leave them to it. It isn鈥檛 complex. The system needs to be plumb and level, and then the panels will slide down the rails.鈥�
Part of the attraction of the systems is that they are very flexible. 鈥淵ou can do long runs 鈥� hundred-metre runs 鈥� and you can do a square pit, eight metres square for tower crane bases, with eight components: four corners and four panels.
鈥淧eople love the speed of it, because if you were to do that in the traditional method 鈥� so sheets, and hydraulic frames for an eight-metre square pit 鈥� you would have hundreds of lifting operations.鈥� And, of course, every lifting operation brings additional risks.
Covid struck as NTS was getting its UK business off the ground (or, rather, into the ground). This was in some ways a blessing. The stop in construction operations at the start of lockdown, gave potential clients time to pause and think about new techniques.
Today, slide rail systems are specified on major projects including HS2. Flannery approached main contractor Balfour Beatty to promote the system and initially got knocked back. 鈥淭hen three years later, the phone rang and it鈥檚 Balfour Beatty asking 鈥榗an you come and tell us all about slide rail?鈥欌��
Today, he says, 鈥淭hey love the product. All the tier-one contractors especially in the water sector, they all love the product.鈥�
It鈥檚 not just the big players that see the benefits though. Slide rail systems do cost, and the longer you have one on hire, the more you鈥檒l pay. But that can be more than balanced out by the speed at which the job can be completed.
鈥淭he smaller companies are interested in the speed. If you want to put a tank in the ground, using traditional methods might take you two weeks. With slide rail you can have it done in a week.鈥�
NTS and Flannery have focused on pure hire, showing the customer how to use the product and leaving them to get on with it. Terra Infrastructure and its sister company AGD are taking a different approach. To Radem盲chers, part of the attraction of slide rail is its modularity, and the engineering challenge of designing a smart solution for customers. Back in the early 2000s, he had taken a job as a trainee at Krings and had been excitedly telling his wife about the company and his prospects.
鈥淪he picked me up at the stockyard, and she was shocked: 鈥榊ou鈥檙e working in a scrapyard!鈥欌�� The components themselves are, to an untrained eye, just a bunch of bits of metal. But like Lego or Meccano, they can be assembled however you like.
鈥淚t鈥檚 definitely not rocket science, but there鈥檚 a lot of engineering and understanding of the whole construction process in it. The job site needs to be economical and so we really put the focus on the consulting,鈥� says Radem盲chers.
One such job was in Aachen, where the new Tivoli stadium was being built. A new trench needed to be dug, 60m long, 22m wide, and six metres deep. 鈥淚t was calculated first with a sheet piling cofferdam. To do the installation alone would have brought them a four-week delay,鈥� recalls Radem盲chers. 鈥淎nd they would have huge penalties, because the season was starting and they had to have it ready for the grand opening.
鈥淲e made a proposal using slide rail, with a special solution specified for the project. They saved six weeks, because of the much quicker installation and extraction of the system.鈥�
Now, Robert Law of AGD plans to offer the same sort of planning to customers in the UK. The starting point was a similar pile of metal pieces to that which so surprised Radem盲cher鈥檚 wife.
鈥淲e bought a load of it. So we鈥檝e got something like 500 tonnes of the stuff on the floor now,鈥� says Law. 鈥淎nd the design is part and parcel of what we鈥檙e offering.鈥�
Along with the design services, backed up by Terra Infrastructure鈥檚 experience and expertise, AGD will be offering slide rail systems on a contract hire basis.
鈥淥ur business is an operated hire business, and has been for many years,鈥� says Law. That approach will stay the same as the company starts offering slide rail systems. 鈥淲e鈥檒l send our excavator and our team to install it for you and extract it as well, if you want us to, at the end of the job.鈥�
While using the slide rail is in many ways a less skilled operation than sheet piling, it still requires a crew that is familiar with the product.
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鈥淚t鈥檚 harder and harder to get good people, full stop,鈥� says Law. 鈥淪o when you鈥檙e talking about a groundworks company, or a tunnelling company, or whatever, it鈥檚 having the people who know how to do this. They might have them today, but they鈥檙e gone by tomorrow.鈥�
Law and his colleagues had just completed their first installation of the system when he spoke to TCI in March. Now, they鈥檙e ready to put their approach to the test.
There are some limits to the slide rail system. As a hire product, whether you are hiring without a crew, as NTS does, or with a crew and excavator as AGD plans to, the longer the job takes, the more it will cost you. So for a project that will have shoring in place for a long time, it may be more cost effective to turn to more traditional systems.
The other challenge is ground conditions. The slide rail isn鈥檛 designed to hold back loose sand or very wet ground. In these conditions, neither of AGD nor NTS would recommend slide rail. Instead, an interlocking sheet piling system is the safest choice.
But where the goal is to get trenches or pits installed quickly and safely, a slide rail system offers real advantages. It can be installed, dismantled, and reinstalled further along a trench quickly, making it ideal for linear projects. For pits, fewer components are needed and less equipment is needed for installation, making it easier to position a tower crane base or to launch a tunnel boring machine.
Where an existing pipe crosses a trench, sheets can be used alongside the slide rail system to fit around it鈥攕omething that can鈥檛 be done so easily with a box shoring system. And, Law says, the flexibility of this modular system makes it much easier to use than box shoring where the line of a trench has a dog-leg. Slide rail designs can accommodate this easily.
All of which means the UK鈥檚 current water crisis presents an opportunity for slide rail suppliers, and the customers that turn to them. Flannery鈥檚 focus is very much on AMP8, the Ofwat-led eighth asset management plan, running from 2025 to 2030, which aims to boost maintenance and capacity after years of under investment.
Right now, projects are in the design stage but once the water companies and their contractors start digging pits to replace pumps, or long trenches to accommodate new large diameter concrete pipes, slide rail systems will be ready to play their part.
鈥淚t will make everybody very, very busy,鈥� says Flannery. 鈥淎nd we鈥檙e very well placed to take advantage of that.鈥�
UK gets a wake-up call
The decision by AGD, and NTS before it, to target the UK market has proved a wake-up call for at least one UK equipment hirer.
Groundforce Shorco, the ground support arm of hire group VP, has sprung into action with the re-launch of its own slide rail system. Supplied in two configurations 鈥� the single slide rail (SSR) and double slide rail (DSR) 鈥� the Groundforce product is in fact the SBH system wearing a different badge.
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鈥淭he re-introduction strengthens Groundforce鈥檚 ability to deliver a comprehensive excavation support offering, alongside traditional sheet and frame methods,鈥� the company says.
The SSR can be used to support excavations up to 3.8m deep and between 1.24m and 6.24m wide. The DSR will support excavations as deep as 5.8m with a working width between 1.24m and 6.24m. Maximum pipe clearance is 5.1m.
Although Groundforce has offered the slide-rail system for several years, the uptake in the UK market has been disappointing so far. Groundforce is therefore keen to tap into any stimulation of demand from UK customers.
鈥淭he UK market has traditionally used sheets and frames to support excavations,鈥� said Groundforce sales director Stephen Cooper. 鈥淗owever, with projects that require greater under strut clearance and faster installation, the slide rail systems can offer a highly effective solution.鈥�