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Jul 20, 2023

Round table: Staying safe

The ground engineering sector sprung to action following a shocking piling rig accident 20 years ago. Recent instances of rigs falling over show that the industry must reinvigorate its efforts to

The ground engineering sector sprung to action following a shocking piling rig accident 20 years ago. Recent instances of rigs falling over show that the industry must reinvigorate its efforts to improve the safety of piling platforms. GE chaired a recent round table on the topic.

In May 2003, a 25m tall piling rig overturned on a Channel Tunnel Rail Link construction site close to the Aveley viaduct in Essex. The cause of the accident was linked to the piling rig working platform.

Following the incident, a year later, the Health & Safety Executive (HSE) revealed the findings of its investigation. The main contractors had failed to reinstate the platform adequately after digging a trench to remove an obstruction under it.

During GE’s recent round table discussion, Network Rail’s Southern Region principal geotechnical engineer and previous Geotechnical Asset Owners Forum chair Derek Butcher said: “You can still take a train on High Speed One along that line and you’ll see where the incident happened. It’s a stretch that runs parallel to the London, Tilbury and Southend railway line. The piling rig toppled onto the running line and brought down all the catenary associated with that line as well.”

Nobody was injured during the incident; however, it could have led to a serious train crash as a passenger train had passed the site only two minutes earlier. The accident led to a three day closure of the line.

The HSE stressed that “better communications, including explanation of safety critical parts of the job and better monitoring of the work would have prevented this incident”.

While much has changed in the last 20 years, similar incidents are still occurring on sites, with at least three piling rigs overturning in the last three years.

The Aveley incident led to the creation of the “BR 470 Working platforms for tracked plant” guidance, prepared by the BRE on behalf of the Federation Piling Specialists (FPS). As part of this, FPS members also stepped up their campaign to ask clients for working platform certificates before the contractors perform any piling. These would confirm that the working platform has been properly designed and constructed in accordance with the design, and that it will be regularly inspected and adequately maintained.

Keller technical director Andrew Heathcote believes the FPS working platform certificate has since become the standard.

“It was the thing that underpinned the improvement in our industry, and it has set the bar for others around the world even,” he said.

“Now there is probably room for improvement, as it tells you how good the platform is and that it’s right before you roll onto it, but what it doesn’t necessarily do as well is pick up on changes to the platform and information on maintenance. There is a register on there, but it’s not very thorough, and I’m not sure it’s audited that closely.”

L-R from the top row: Derek Butcher, Yvonne Ainsworth, John Chick, Graham Hall, Andrew Heathcote, Steve Hadley, Yuli (Chaido) Doulala-Rigby and Dave Woods

Tensar chief civil engineer and British Geotechnical Association vice chair Yuli Doulala-Rigby however asked: “How do we make sure that everybody uses the working platform certificate? How do we enforce it?”

She continued: “Is it mandatory for every subcontractor? How do we approach these people who are not in the know? The certificate works for us, but we need to make it mandatory for all.

“The BR 470 has got all the details, and the Temporary Works Forum’s (TWF’s) good practice guide explains the importance of the platform fill and tells us exactly how to specify it, but how do we enforce this guidance to be followed on site? I think that is the biggest problem.”

Expanded Geotechnical business leader and FPS chair John Chick answered Doulala-Rigby’s initial question: “Is it mandated? No, it’s not. And in the last year, I’ve heard twice now people saying that they’d been told by the client that they don’t have to follow it. One of them was an FPS member who then stopped working and would not carry on without the certificate.”

Heathcote is currently heading up an FPS technical committee working group that will be working in partnership with the HSE to pull together a safety bulletin around some of the more recent rig overturning incidents, while also providing guidance for platform installers.

Central Piling managing director and Ground Forum chair Steve Hadley said: “The FPS is currently active with the working a group, and we are concerned about the incidents that have happened recently and the potential catastrophic consequences that could come about.

“So clearly the message isn’t getting through to everybody. And the areas that I’m particularly concerned about – having gone around sites recently – include the quality of the material that’s being used, the thicknesses of the platforms, and the general procedures of getting platforms designed and signed off by client.

“Clients are expecting to have to sign [the certificate] and there doesn’t seem to be much pushback. They understand that there is a responsibility – now whether the person singing it entirely understand what they’re signing is a different issue. Maybe there’s more education we need to do with our clients.”

Steel Piling Group chair and Fussey Piling managing director Graham Hall said: “As a sheet piling contractor, we always say that the biggest risk on any job is the piling mat. Now that’s a well rehearsed discussion we have with many, many clients, but it’s the one thing that many clients want to cut back on all of the time.

“We ask for an 8m wide piling mat for our operations, which is wide enough for the rig, crane and whatever you’re doing. But then when you get on site, it’s nearer to 6.5m wide. You can still get your rig on it, but there’s not quite enough space to manoeuvre. Even worse than that is that some operators of the Movax type side grip excavator mounted machines will often just work on mud, and you’ve got a 5t driving attachment hanging around on the end of a 35t excavator, with an up to 2t sheet pile or H beam – all that weight – and they’re just happy to travel around all day on mud. One of those is going to go over – and probably has gone over, but it’s not been publicised.

“We’ve produced a guidance note at the SPG on the importance of having a piling mat for excavator mounted piling equipment.”

Heathcote commented: “Graham is talking about the extreme of not having a platform, but part of the reason we’ve put the FPS working group together is that there are a lot of common themes – one of them is the material quality, which seems to be a recurring one across all of the members of the FPS.”

The European Federation of Foundation Contractors (EFFC) and Deep Foundations Institute (DFI) are also working on updating their “Guide to Working Platforms”, which was originally released in 2020. The joint task group is looking to compare different testing methods for working platforms that can ensure they are fit for purpose, as well as being quick and low cost. In addition, the group is investigating how different working platform design methods can produce more consistent results by doing a sensitivity analysis on the input parameters.

Chick also wanted to highlight the attitudinal change that has occurred in recent years, as well as a loss of awareness of what can go wrong if the platform is not adequate.

“And it’s only going to get worse, because there’s a bit of an arms race in plant with rigs getting bigger, masts getting taller – particularly in the CFA [continuous flight auger] market. You’re now looking at rigs that are 36-37m tall – if that goes over, that’s going to land two streets away,” he said.

Doulala-Rigby added: “Some people criticise the EFFC guide because it has an image with blood on the asphalt, saying that it’s too gruesome. No, it’s not – this is exactly the consequence that people really have to understand. People will die if things are not getting done properly.”

She further stressed that education is required, particularly targeting smaller ground engineering firms that might not keep abreast the latest industry developments. She believes the industry needs to have mandates, and prosecution should be a real possibility.

“We need to make people afraid of the consequences; it’s the fear of the law that makes people follow the rules,” she added.

“Those of us who represent industry bodies and associations, we are the ones who need to make decisions and enforce this mandate.”

Key issues that have come to the fore in recent years include the scarcity and cost of good quality fill material for the working platforms.

“When I first walked onto a piling platform, it was concrete, rubble and demolition waste,” said Gavin & Doherty Geosolutions managing director for onshore Yvonne Ainsworth. “Generally, in the noughties, the platforms, if they were designed properly and they were installed properly, they functioned perfectly.

“What I'm seeing now is that we haven't got any crushed concrete anymore; that material isn't available. So, we have to make do with something else.”

Material being delivered for projects often complies with the 6F5 specification - based on National Highways’ Series 600 document - meaning it does not have too many fines, but it could effectively be "play sand”, Ainsworth said.

She stressed that a “better materials specification” is needed, as 6F5 is “no longer fit for purpose for piling platforms”.

She added: “Sustainability has made us look very carefully at the platform designs. There have been complaints that the piling platforms are over designed and conservative. Geogrids are a great way of reducing the thickness, but we need to be very careful on that aspect because people got so used to having that buffer, that safety factor in the platform, due to the conservatism of BR 470.”

Heathcote picked up on the point of conservatism in design, saying: “It’s important to make sure you’re not over specifying platforms, because there are sustainability and commercial aspects to that, but you can’t look at that in isolation; you’ve also got to consider that you’ve got a 100t machine on it and it is going to dig that platform up. If you’re going to go with a very tight design, you’ve got to look at the quality of the material and also how you maintain it.”

Ainsworth commented: “When you’re the designer, the consultant, you have no influence over the material - you specify it as 6F5 but you have no influence over where it comes from and what it looks like – and you have no control over the maintenance.

“I’m not saying it’s too conservative; I like BR 470 because it gives a buffer for human error. I think we need to bear in mind the fact that people are trying to squeeze it down, and every 50mm on a big platform will count, as it will drop the price and make it more competitive. So, there will be more pressure to get it as thin as possible.”

Doulala-Rigby responded to Ainsworth’s point about geogrids: “Thin platforms stabilised with geogrids are not the problem; we have been doing this for over 30 years saving hundreds of thousands of cubic metres of fill with no failures. Key issue for all geosynthetics’ performance in working platforms is the fill; we need to 100% understand the type of material used. When I joined Tensar 17 years ago, it was all crushed chunks of concrete, and that was much better than the finer material we see now.

“I fully agree the 6F5 is not fit for purpose anymore. One approach could be for the industry to build a specification from scratch based on previous experience and suggested requirements in recognised guidance. The TWF guidance does mention 6F2 and 6F5, but it recognises it’s a broad band of materials. So, we need to do something. But not just us, the whole industry.”

She added: “Another important issue to stress here is that while all geosynthetics work, their performance can dramatically vary from one product to another as different geogrid/geotextiles interact and perform in a different way with the fill. So, for safe platforms, we need to make sure that any ‘swap’ of geogrid/geotextile and/or fill material, must be accompanied by the appropriate bespoke design, as stipulated in TWF good practice guide and CDM regulations."

Chick contended that, in addition to the materials issues, the procurement and programming of the works can also create challenges.

“We probably need to be more vocal early on, as the procurement route chosen sometimes doesn’t help. If you have demolition and enabling packages let together, while laying the piling mat might be by somebody else before the piling contractor comes in – there’s an inevitable disconnect, which is a recipe for creating soft spots and leaving obstructions under the piling platforms.”

International Geosynthetics Society UK chapter chair and Huesker technical manager Dave Woods also highlighted that the problem might be linked to an unwillingness to provide full ground investigation for a site, particularly of areas with only temporary works.

“When we're dealing with heavy rigs, we really should be looking far deeper into the soil; it should be a proper site investigation to see if there is soft alluvial material or peat or something underneath the site that's going to be affected by the larger pressure bulbs that we get underneath the tracks of these heavier machines that are penetrating a lot further into the soil,” he said.

Hall noted: “From what we see on site, the piling mat is designed for the loadings that that we give for our rigs and equipment. But before we turn up and put a rig or a crane onto that mat, it's normally plate load tested anyway. And then if there's any significant change through maintenance or whatever, then we step back and ask again whether we can do a plate load test. So, in response to Yvonne saying you specify and design the mat, there must be some testing to verify what you've designed. I know some people will just install a mat to the design and as far as they're concerned that will sign the working platform certificate off. But perhaps by tightening up those guidelines to say each mat must be plate load tested as opposed to just designed and installed, as per the design. Is that a way forward?”

So, which stakeholders on a project should ultimately take ownership of the safety of these working platforms? And what can the industry do moving forward to improve safety?

“In terms of ultimate ownership, the people putting those rigs to work – we are those people,” Chick answered. “We need to own the message and push back very hard if we’re expected to work on an unsuitable platform or using an unsuitable material. Aveley was the shock that woke up the piling world; I think we need to remind people of that before we have another shock.”

Hall added: “With respect to the responsibility, it's unfair to expect the designer to actually be on site, as they might be sat 100 miles away. It then has to be passed down to the contractor to take responsibility to install that mat and test it to the requirements of the design. And therefore, if a rig fails, which hopefully it won't, 100% that that goes back to the contractor in failing to install it correctly.”

Butcher continued: “Aveley happened 20 years ago - and the industry learned and moved on. It would be worthwhile that new starters to the industry look back on it to understand some of the issues we discussed. These are often difficult to explain in design codes and standards.”

Doulala-Rigby stressed that the client needs to be a part of the discussion. “We need to stop contractor self-certification,” she added. “The designer is not there, and the subcontractor sometimes is not strong enough to say ‘stop the works’ because the material is not suitable. My view is that an independent person is needed on site to do this.”

Woods agreed that the absence of an appropriately qualified groundworks supervisor is a key challenge.

He said that on top of a third party checking the design, a groundworks foreman should be appointed on sites to “ultimately sign off on the rig loading, design certification and check and supervise the depth and quality of the platform installation and quality of fill material”.

Hadley also believes that the industry needs more education about alternative design techniques using geogrid reinforcement, and dynamic testing to cover wider areas in a way that is more representative of how rigs work.

Doulala-Rigby noted: “Education is important, but I’m not sure how you reach every little contractor and subcontractor out there. So we need some form of heavy financial repercussions."

Instead of fines, Ainsworth however believes that reputational damage will be a bigger deterrent for the industry.

She also added: “I think we will not get around writing a new specification for the material. That will require lobbying, and it probably needs to involve National Highways, because their specification is what everybody goes to, the Series 600.

“If we want to create a change, by having better material, for me that’s the only way – by getting it implemented into Series 600. Then the quarries will produce it, because it becomes the standard and it won’t have a negative commercial impact on procurement as it is a ‘standard’ material.”

Earlier this year, the FPS launched a safety training video on the topic of working platforms. It was produced to bring clarity and guidance to this known area of safety concern, following a number of incidents related to large plant items overturning in recent years.

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