Have segments turned a corner? · They could potentially allow a one-pass lining, saving the...

38 Tunnelling Journal

The first SolidCast Polymer manholes were installed in 1998 as part of the Greater Houston Wastewater Program. The City of Houston was looking to trial new products and so borrowed the polymer concrete structures from the chemical processing industry, where they had been used successfully for years in highly corrosive environments.

From polymer concrete manholes, surely the next logical step is to polymer concrete tunnel segments? They could potentially allow a one-pass lining, saving the materials and time needed to add a second lining to protect the first against corrosion.

It’s a step SolidCast Polymer president Rich Cubeta has been eager to take for a long time, but to date polymer concrete segments have been considered too expensive. “It’s been talked about a lot, but it’s just economics,” says Jon Kaneshiro, technology leader for tunnels, at Parsons.

That could be set to change, thanks to a new idea that significantly cuts the amount of material

required. Currently SolidCast Polymer segments are under consideration for a deep waste water project in Dubai, where Parsons is responsible for design, programme management and construction management.

It does feel like the pace of change is quickening generally in this field. Other areas where advances are being made include the use and understanding of fibre reinforcement, new forms of hybrid, integrated protective linings and testing technology.

There are several reasons for this: we are building more tunnels globally as populations migrate to cities and authorities need to move infrastructure, services and other facilities underground. Communication is faster and easier, with information being shared informally, as well as formally, on platforms like LinkedIn.

Despite the fear factor, some owners have a public innovation agenda. And, while procurement methods and forms of contract may not yet be

Have segments turned a corner? Materials and technologies that speed up installation and lower lifetime costs are finally coming of age. By Kristina Smith.

Tunnelling Journal 39

entirely helpful to that aim, it does mean that more consulting engineers and contractors are working to push new ideas forward.

Kaneshiro also highlights growing environmental conscience: “Concrete has a tremendous carbon footprint, which is another reason why these polymer resins need to be looked at,” he says. “I would like to see a paradigm shift.”

Slimmer and strongerFor a corrosive environment – such as a waste water tunnel – polymer concrete would be ideal. Cubeta says that 300 years-plus is a very conservative estimate of its life, a statement that he says is backed up with research. But there are other benefits too.

Because polymer concrete is so much stronger than Portland Cement concrete, polymer concrete segments could be far thinner, Cubeta reckons a three-inch (75mm) thick polymer segment would be equivalent to 11 inches (280mm) in concrete. However, there’s a caveat:

“You can go a little bit thinner but you still need the area to thrust on,” explains Kaneshiro. “You might be able to save a couple of inches.” Dowels and gaskets must be accommodated too.

Cubeta considered ways to reduce the amount of polymer used per segment. Adding waffles to the outside face was rejected because it could hinder the flow of the anulus grout; waffles on the inner lining would impede the flow of the water within.

Then he came up with the idea of using cores, formed with cores made of light-weight materials such as Styrofoam, to reduce the volume of polymer used, a technology he calls QOR-TEC which he eventually managed to patent recently. “We found out that by including the cores, we lost less than 5 percent of the segment’s load-bearing characteristics,” says Cubeta. “If you did the same thing with Portland Cement concrete, you lose almost 50 percent.”

The polymer concrete segments would be far lighter than standard ones too, making handling easier and they are faster to manufacture. “We can cast these materials and then in five or six hours pull them out of the mould. In seven or eight hours, the material will be cured. There’s no need for an oven,” says Cubeta.

With the capital cost reduced thanks to QOR-TEC, Cubeta hopes he has cracked the market this time. “It’s pretty frustrating,” admits Cubeta. “If I’d come up with this idea ten years ago, we could have won those jobs.”

Time and schedule savingsAnother idea which allows a one-pass segmental lining to be used in aggressive environments is to cast the protective layer into the concrete segments. This isn’t new – it’s been at least ten years in the making – but incremental developments are moving it on.

There are two recent projects to talk about: Contract 2 of the Twinning of the West Trunk Sewer Project for the Region of Peel in the US and the main trunk sewer for the Inner Doha Re-sewerage

Implementation Strategy (IDRIS).One of the earliest uses of this type of system was

on the Upper Northwest Interceptor in Sacremento in 2009 when Ameron’s T-Lock PVC liner system, commonly used with cast-in-situ linings or precast pipes, was cast into segments, and the joints welded on site.

The first version of Herrenknecht’s Combisegment were also used in 2009 on the Yuzhny Sewage Pipeline in Tzariayno, Moscow. These featured a GRP cast-in liner, which proved to be too rigid; the materials is difficult to get into the moulds and can break is something heavy is dropped onto it.

The latest Combisegment has an HDPE liner which is far more flexible. The other improvement is that the EDPM gasket is integrated into the plastic liner during the first step of the manufacturing process so that no welding is required. This version is being used for the first time by Technicore Underground on a section of the West Trunk Sewer Project, a 3m-diameter tunnel which runs mostly through shales, with some mixed ground, and water pressure of up to 2.6 bar in places.

“There was a little bit of a learning curve but once we went past that, it went fairly well,” says Technicore CEO Tony DiMillo of the Combisegments.

One of the first issues came during the

HAVE SEGMENTS TURNED A CORNER

SolidCasy Polymer’s QOR-TEC technology could make polymer concrete segments a viable and longer-lasting alternative to traditional ones.


casting process itself, which was done by Ewing Fabricators, part of the Technicore group of companies. The HDPE lining material was distorting due to the heat of hydration.

The supplier’s solution was to heat up the material and cut it to size at a higher temperature before it was put into the injection mould. However, this approach was not ready in time for the first of the two sections, so Technicore had to cast the linings in without attaching them to the gaskets and weld the joints afterwards.

There were a few challenges during installation too. There was difficulty with the vacuum erector which wasn’t always able to get a good seal on the HDPE. “That did slow us down but overall it was only 85 rings so it was not too bad,” says DiMillo. “If I were to do it again I’d probably go back to the old way of using a ball and grab system.”

The tunnel segments on the IDRIS-MTS01 project have to cope with a tougher environment than those in the West Trunk Sewer. Externally, there is up to 5 bars of pressure with ground water that can contain salts, sulphides and chlorides and internally the presence of hydrogen sulphide gases.

Using an integrated HDPE liner on the project brought significant time and cost savings compared to the original design which called for a 250mm thick secondary concrete lining with protective HDPE liner. It decreased the overall lining thickness by 200mm which, in turn, reduced the excavation quantity by 20 percent and meant the Bouygues Travaux

Public and Urbacon Trading & Contracting JV could use two TBMs rather than four.

“The removal of the secondary concrete lining – which represented between three and five months on the critical path after the TBMs had finished their drives – was a key element in securing the overall programme,” says Thibaut Lockhart of Bouygues, who was technical manager on the project.

But the decision to cast the HDPE into the segments was driven as much by quality considerations as cost, says Lockhart: “We knew it would be complicated to cast this kind of secondary lining to guarantee the quality of the concrete,” he says. “If you are doing a 16km-long tunnel, there are bound to be issues with quality at several points that have to be repaired.”

Bouygues looked at the Combisegment system but were not confident that it was the right solution for IDRIS, says Lockhart, due to site-specific constraints. The resin used to overmould the gasket and to achieve connection with the membrane did not meet the durability requirements. Tests showed that if the TBM rams were not positioned correctly

and pushed directly on the resin frame, the joint would crack open, compromising the lining’s watertightness.

Rather than suction pads, the TBM’s mechanical erector lifted the segments

via an attachment screwed into an HDPE socket cast into the segment and

welded to the membrane before the concrete is poured. These sockets

were also used to support the TBM services to avoid drilling through

the membrane, once the segments were installed.

Bouygues’ system did require 2.5km of

Technicore used Herrenknecht

Combisegments on the West

Tunnel Sewer Contract 2 in Mississauga,

which requires no welding because gasket and liner

are joined during the manufacturing

process


We’re all about communicating. Clearly!

welding, 2km more than would have been required for the cast-in-situ secondary lining. Special training of the welders by the HDPE supplier ensured that this operation went smoothly.

One challenge for any cast-in lining system is how to check the integrity of the segments, as the concrete is hidden behind the membrane. On IDRIS-MTS01 Bouygues carried out destructive testing of a few segments initially to validate the segment fabrication process, and then random tests on segments at regular intervals throughout the precasting period.

Bouygues researchers are working on a non-destructive test method that uses terahertz imaging and tomography, using the lower band of infrared light. “We can see very clearly the studs on the back of the membrane, the joints between segments and the erector screws, down to a resolution of about 0.5mm. But we need to get down to 0.2mm or 0.1mm to be able to see cracks,” says Lockhart.

Both Technicore and Bouygues will look to use integrated lining systems again. Bouygues is already looking at tenders in the Gulf and elsewhere where the system could be used.

“Compared to the alternatives right now, it’s the best way to go,” says DiMillo of the Combisegments. “The section of the tunnel where we had to weld afterwards was painful. I wouldn’t want to do that again.”

Jon Hurt, global tunnel design leader at Arup, who was Technicore’s designer on the West Trunk Sewer contract says that the system is under consideration of the Silicon Valley Clean Water Pipeline along with a conventional two-pipe solution and a system that involves including sacrificial concrete on a single lining thickness.

“One of the challenges you have to think about with a cast-in HDPE liner is that if the tunnels are

deep you have to make sure there’s enough bond between the concrete and the HDPE so that it doesn’t de-bond,” says Hurt. “The West Trunk Sewer tunnel was low load, in relatively stable ground with fairly low permeability.”

Fibres: design moves onWe can’t claim that fibre reinforced tunnel segments are novel. According to new design guidance published by the Fédération internationale du béton (fib) in October 2017, the very first fibre reinforced tunnel segments were used in Italy as early as 1982.

The fib Bulletin 83, ‘Precast Tunnel Segments in Fibre-Reinforced Concrete’, lists 77 projects which have used fibre reinforced concrete (FRC) and shows that their use has increased dramatically over the past ten years. It also gives very clear design guidelines for owners and designers who want to work with fibre reinforced segments.

“It’s a nice piece of work,” says Colin Eddie of Colin Eddie Consulting. “It was compiled by Professor Alberto Meda who has probably brought the clearest thinking to this subject.” Meda headed up a panel of experts, with representatives from the US and Japan as well as many European countries.

“It’s a powerful document for promoting FRC and precasting,” says Benoit de Rivaz, global business manager for Bekaert Maccaferri Underground Solutions. “It provides detailed design cases, durability requirements, fire. People will feel safer with this document to hand.”

The Grand Paris Express metro project will use FRC segments for the first time. “It’s a huge project and a big breakthrough for it to be using FRC because the Paris administration was seen as very conservative,” says de Rivaz. “If Crossrail in London and now Paris are using FRC, that will influence other countries.”

The US is a growing market for Bekaert Maccaferri. Last year it set up a manufacturing facility there, timely in the face of President Donald Trump’s ‘Buy American, Hire American’ campaign.

Bekaert Maccaferri has also launched a new, stronger version of its 4D fibres most commonly used in segment, the 4D 80 60 plus. “The higher tensile strength is required to take into account the evolution of the concrete mix designs which are getting stronger,” explains De Rivaz.

In Australia, the new fibre is being used for the first time in segments for the Perth Airport Link, being constructed by Salini-Impregilo and NRW. Bekaert


Bouygues designed its own system of integrated HDPE liner for segments for the IDRIS-MTS01 project in Doha.


Maccaferri has won a second project for the Sydney Metro which will start in May this year.

Though macrosynthetic fibres are a far less mature technology than steel ones, the use of these is now spreading. EPC, which supplies macrosynthetic BarChip fibres, has secured its first contract in North America, a 2.75 ID CSO storage tunnel which will have 7kg per cu m of Barchip fibre with the first rings expected to go in during June.

“It’s a big step for North America, especially given that they have produced guidelines for segments made of reinforced concrete which only talks about steel fibres, not plastic ones,” says EPC group chief engineer Ralf Winterberg. He refers to the American Concrete Institute’s 554.7R-16 Report on Design and Construction of Fiber-Reinforced Precast Concrete Tunnel Segments, published in 2016.

EPC, which is negotiating for a second segmental tunnelling project in North America, got its toehold in the region through forming strategic partnerships with progressive design consultants. “Many companies like to embrace new technology,” says Winterberg. “They are looking for innovative ideas that can bring benefits, such as the durability plastic fibres bring in corrosive environments.”

New hybridsProfessor Meda, with others from his university, has been researching the use of fibre glass reinforced polymer (GFRP) reinforcement for several years. GFRP reinforcement could work well in environments where steel might corrode or where segments are later broken out, for example for cross passage construction.

Some of Mesa’s latest research looked at what patterns of polymer bars worked best, carrying out large-scale tests on metro-size tunnel segments. University researchers are also looking at combinations of light GFRP cages and high-performance steel fibres.

EPC is also researching the use of GFRP and macrosynthetic fibre hybrids. It is working in

partnership with an Italian manufacturer

which can produce closed links in GFRP. “It’s new

technology. We are waiting for a patent,” says Winterberg.

“The target is to have light cage concentrated along the ring joint. Fibres do the general work but you have extra reinforcement where you need it,” says Winterberg. “If you have big segments, bending moments get large, and the risk of damage rises exponentially. If you are looking at tunnels larger than metro, you cannot do fibre only, you need extra reinforcement, especially for the handling cases.”

The use of hybrids of traditional rebar and steel fibres has increased over the past decade too. Marti recently produced the most heavily reinforced hybrid segments it has ever made, for Switzerland’s largest diameter tunnel to date, the Belchen road tunnel which was bored with a 14m-diameter Herrenknecht machine. The geology here is complex with folds and faults and swelling rock.

There were three types of segment for Belchen, with between 110kg and 240kg of reinforcing bars per cubic metre and a further 30kg per cubic metre of fibre. “The challenge for us was the concreting requirements, combined with the fibres,” says Paul Freudiger, Marti project manager. “With the huge amount of rebar, stiff concrete and fibres, we had to increase the vibration time quite a lot.”

Following on from the Belchen tunnel, Marti manufactured the segments for the Eppenberg tunnel at the same facility. These tunnels were traditionally reinforced with no fibres, but did involve some ‘firsts’.

It was the first time a cast-in gasket had been used in Switzerland. Marti used gaskets from Datwyler.

Marti also worked with supplier Optimas to develop a new clip system, called Breakaway Sockets, for fastening accessories into the segments. “Rather than using bolts, you just clip your item into a special socket that you weld into the formwork,”

Segments for Switzerland’s

14m-diameter Belchen Tunnel,

constructed by Marti, are

reinforced with both rebar and

steel fibres to cope with the

forces from the swelling ground.



explains Freudiger. “When you take the segment out of the framework, the plastic clip just breaks, whereas with bolts you have to take time to unfasten them first.”

As a manufacturer of segments, Freudiger would always like to see hybrid reinforcement for larger diameter tunnels. “I don’t like to go into a tunnel and see segments that we have perfectly produced with damaged corners and damaged edges.”

Segment damage, usually during erection and shoving, is a universal problem. Eddie cites a study where several contractors pooled their data and showed that in general there is damage to a segment every six rings.

All things considered, hybrid segments should not be more expensive, says Freudiger: “In my opinion, it does not cost more. You have to do the calculations. The amount of rebar is reduced when you add fibres and you have a better product and its better protected so less time and money is spent on repairs.”

Researchers at Ruhr-Universität Bochum are looking at ways to concentrate fibres where you need them, looking at processes that mix two types of concrete as it is poured into the mould – ‘fresh on fresh’ - and also investigating using precast elements with fresh concrete, ‘fresh on solid’. Sven Plückelmann, with others, has been working on the latter case, looking at the best way to bond the precast elements with the fresh concrete and seeing how small samples performed under loading.

“Due to surface roughening of the precast components, we found that a sufficient high bonding could be achieved under tensile loading,” says Plückelmann. “We also found that Concentrated pre-loads, simulating the jacking forces, can weaken the bonding strengths.”

Plückelmann’s research is part of a wider programme which aims to enhance the safety, durability and roughness of hybrid lining segments. Next steps will see full-size segments produced and tested.

Digital accountabilityThe other area where strides are being made – though there isn’t space to report in detail here – is in the monitoring of segments during construction and in service and how that data is analysed and used. Technologies including fibre optics and non-destructive testing offer the opportunity to feedback performance data into the design process.

Bouygues Travaux Public installed fibre optic instrumentation into three fibre reinforced test rings, installed on Paris’ Line 14. The assurance this gave as to the segments’ performance means that the client can confidently allow the use of such segments on the hundreds of kilometres that will form the Grand Paris Express.

With the progress of digital construction – the way we analyse, use and share information – it will be possible to keep a much more complete and detailed record of the structures we are building. Drones and remotely operated vehicles mean that inspections can be carried out far more frequently, so we can ‘see’ how tunnels are performing.

Ultimately this means that lessons can be learned more quickly – although the perennial challenge of how to share failures remains. Certainly, if owners are more able to measure and record the state of their tunnel lining, they can write specifications and contracts accordingly.

Marti trialled new Breakaway Sockets from Optimas on the Eppenberg Tunnel segments, clips that snap off as a segment is demoulded, speeding up the manufacturing process

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