Concrete can be supplied to tunnel projects from commercial ready-mix concrete suppliers to specification. Alternatively an on-site or nearby batching plant can be justified by the economics of scale, the remoteness of the site or special mix considerations. CIFA offers a wide range of equipment applicable to concreting in tunnels including formwork, transport products, mobile mixers, pumps and batching plants. Depending on the design, these plants are made to produce output according to changing requirements and improve overall efficiency, especially in supply.
Transport
The main practical choices for getting concrete to its point of use in tunnels are greatly affected by the section of the tunnel and where it is practical to locate the batching plant. Depending on the logistics of the tunnel, drop-chutes, hopper or mixer trucks on rails or tyred vehicles, belt conveyors, and long distance pumping can all play a part.
During construction of the railway extensions to London’s Heathrow Airport Terminal 5, concrete pumping specialist Pochin supplied a static pump with 240kW diesel drive with site operator and 1800m of pipe to deliver concrete over this distance, claimed to be a record. The US$367,500 contract surpassed previous record work for Balfour Beatty on Terminal 4.
Pochin’s fleet features the Putzmeister PUMI combination truck-mounted concrete pump and mixer. The compact 8-wheel vehicle has a turning circle of 21.5m and carries the TMP 60 CS pump and TMM 21 boom. Output is up to 56m3/h and a maximum delivery pressure of 57bar. The Z-fold boom system carrying a 100mm diameter delivery line has a vertical reach of 20.6m and a net horizontal reach of 14.5m.
Maxon Industries, based in Indiana, originally developed open-top concrete transport dumpers for paving, and then developed Agitor models which prevented the mix for separation over long transport runs. Underground activities began with the 1980s development of the Maxcrete, a low-profile, open-top carrier for mine development featuring a full-sweep paddle design for complete remixing/retempering of the concrete. These units can be skid-mounted or carried on rail or tyred vehicles. Recent developments include:
• a patented high-dump swing-away chute for Agitors
• a self-powered Mobile Maxcrete specially for tunnelling
• the Maxon Maxslide that can dump to either side and rear of the carrier on a turntable arrangement
• employment of a Maxcrete as a surge hopper for a concrete pump whilst being reloaded by Agitors or rail wagons for rapid concrete placement
The Mobile Maxcrete can travel at 10mph on a bi-directional chassis running on the tunnel invert. Maxon also has a range of concrete handling and placement equipment especially for small-bore tunnelling.
As one of the best known manufacturers of rail-based equipment for tunnelling and mining Mühlhäuser supplies specially designed cars for concrete transportation including remixers, silo cars, and cars for ingredients such as aggregate and cement.
Placement
One of the latest applications of Putzmeister concrete pumps and placement equipment is the 12.8km long Lainzer Tunnel for trains through Vienna. Models employed include the BSA 2109HE pump and the models BSA 1408 E and BSA 2104 HP E. The first pumped concrete over 350m at rates of around 40m3/h.
Segment backfilling was another recent project for six Putzmeister KOV DUO 550 PM pumps on Madrid’s M30 tunnel project. The pumps are equipped with ball valves to control the pump in feeding two separate delivery lines. Four further KOV 1050 ball valve pumps were used to transport mortar material from silos, with controls integrated with the other six units on the TBM back-up system. The system was used over three shifts, seven days a week. The FCC-Dragados contracting consortium also leased a truck-mounted Putzmeister concrete pump from Ibérica de Bombeos Especiales for various other concreting jobs on site. This included feeding a BSA 2109 stationery pump from the tip of its boom for long-distance pumping. In a relay operation this delivered the concrete up to 600m through a SK pumping line.
Since becoming part of the Putzmeister group in 2007, Allentown (now Allentown Shotcrete Technology Inc.) has been offering the Putzmeister range of BSA trailer concrete pumps and Snorkel distributors. Although mainly for wet process shotcreting, these units are also applicable to concrete placement duties in major projects.
The largest trailer pump in the range is claimed to offer the highest pressures and outputs available today, with a maximum theoretical pressure of 220bar and maximum delivery of 102m3/h on the piston pump from a 470kW Caterpillar diesel drive. The TSV 5-12 Snorkel, as the largest standard distributor unit in mounted with rails together with a extendible pipe scissor system, also on rails, and powered by a 15kW hydraulic power pack. The telescopic ‘snorkel’ unit can turn through 360 deg. The pipe diameters are 125 or 150mm.
Concrete Pumps of Durban, South Africa, has been supplying the simple and economical air-powered SEM concrete placer pump for forty years. Since the 1980s it has added piston-type concrete pumps including models from the Putzmeister and Thom Katt ranges. The Company also proposes solutions to concrete placing problems and commission the equipment until it is successful.
SEM Concrete Placer Pumps are said to cost only 10-13% of the price of a conventional piston pump, and has no moving parts to maintain or break down. The pumps can operate continuously or in several plug batches, the latter to enable the maximum placement distances and heights to be increased. So far up to 400m horizontally has been achieved. SEM Pumps have been used as trailer-mounted units on the Khimti 1 hydropower project in Nepal, and for a new underground pump station at the Blyvooruitsicht gold mine, South Africa.
The latest model from Tek.Sp.Ed under the Bunker trade name is the versatile B100XP combined mixer, pump and spray system that can handle shotcrete and plastering as well as concrete placement. The diesel hydraulic drive, trailer-mounted unit is designed to mix on-site. The mixer has a 350l capacity, a screw pump, and a loading skip with a digital weighing machine. The pump has a maximum theoretical output of 250l/min with a maximum pressure of 12bar, pumping distances can be up to 60m horizontally and 20m vertically.
With a catalogue of over 20,000 part numbers, Construction Forms (Con Forms) of Wisconsin, US, offers a very wide range of piping systems used in concrete mix transport and distribution. This includes a special Tunnel Placer design to meet the requirements of each project. Features include a boom to rotate through 300 deg., jib extensions such as horizontal and vertical scissor systems, and various power options. The Company has a European operating division in the UK and Con-Forms Asia based in Johor Bahru, Malaysia.
Formwork
In order to cast the poured concrete tunnel lining or other construction into the required shapes, thicknesses and perhaps surface finish, some type of formwork will be necessary. This could be custom designed and made on-site, employ a proprietary modular system of standard components, or use various types of specialised tunnel standard or custom designed formwork. Site fabricated formwork is generally non-viable except for small constructions, by site assembled modular systems are widely used for cut-and-cover tunnels and non-standard sections. Some manufacturers design specially systems for arch shapes.
Specialist tunnel travelling formwork is viable for longer runs of tunnel, and can be easily renovated for use in subsequent projects. The ‘travelling’ principle of location and erection offers several advantages but principally timesaving. Ceresola Tunnel Linings Systems offers formwork of steel and steel/timber combinations to custom designs or standard sections. Types include formwork for roof vaults, inverts, and full sections, suspended slabs, niches and cross passages, together with similar products for erections concrete reinforcement and exterior forms for ‘false’ tunnels and ava-lanche protection. Recent applications include California’s longest highway tunnel, the Devil’s Slide Tunnel, and the Weinberg Tunnel for the Swiss Federal Railways in Zurich. The Devil’s Slide twin-bore tunnel uses two steel forms 10m wide x 8m high and 12m long. The order also included a rebar placing gantry, three concrete curing gantries with controls to prevent microcracking, and special forms for niches and by-pass passages. The Weinburg order included and invert form for the 5km long TBM drive.
Doka‘s large-area Top 50 formwork, often used in tunnel construction, features made-to-measure designs from a modular system of only three system components including timber beams. The shape, size, anchor pattern and sheeting of the panels adapt to suit any set of requirements. The many recent tunnel references include the Lötschberg Tunnel in Switzerland and, in cut-and-cover, the twin-tube motorway Steinhaus Tunnel.
Part of the Lötschberg base-rail tunnel featuring Doka formwork was the Adelarain Fork where an adaptable travelling formwork unit was used with Top 50 large-area formwork to line the funnel-shape cavern at Frutigen. Within a length of 275m the SATCO joint venture formed a circular section funnelling from 18.1m to 7.6m wide and 9.95 to 7.95m high. The formwork was folded down hydraulically and re-erected after each pour. For the Steinhaus Tunnel Top 50 was used in more conventional rectangular sections over 2400m but to form the concrete in a single pour as a ‘White Tank’ impermeable mass with no additional waterproofing skin. All formwork movements were controlled by a single steering unit to move to the next pouring step.
A trend to ‘fair-face’ concrete for architectural aesthetic properties using only the right concrete as a material can also be involved in tunnel construction in, for example, metro stations for public access, improve lighting or a better surface for decoration. Both Doka and PERI are among those meeting this need. As part of the B17 ring road around Augsberg, Germany, Züblin used formwork based on Peri’s GT24 girder system with a hydraulic formwork machine to carry out weekly pours. The cut-and-cover construction was set in an excavation supported by overlapping bored piles and sheet piling. To ensure water impermeability the closed-frame construction used waterproof, reinforced concrete, with monolithic pours of the base and walls avoiding construction joints.
Materials
As for concrete for spraying and pre-cast construction the mixes used for cast in-situ concrete will be designed to meet the peculiar conditions of transport, placement and performance required once cured. In this context retarders and plasticisers to promote and extend work-ability and pumpability are likely to be of importance.
Whilst the inclusion of fibres is often associated with sprayed concrete, the products of Bekaert and IFT Fasertechnik have been used for cast in-situ linings. Steel fibres have been used to improve the toughness of concrete, especially near the surfaces, and sometimes supplement or replace conventional reinforcement. Polymer fibres have also been used for structural and fire alleviation purposes.
IFT’s Duoloc steel fibres provide ‘double locking’ in the mix by hooks at both ends of the fibre and corrugations along its length. Unoloc is a version only with end hooks. Duoloc is also available in Trioloc mixes in combination with Polyloc polypropylene fibres. Microloc ultrafine polymer fibres are also available for the alleviation of possible fire damage.
The frequently tricky problem of TBM entry and exit points in shafts has been tackled by the development of ‘soft eye’ structures for easier, sealed passage of the TBM cutterhead. The thick-walled weaker concrete approach of early developments has an alternative with the production of glassfibre-reinforced plastic (grp) reinforcement panels as produced by Fortius of Belgium and Sireg of Italy. Such panels made from Fortius Aslan 100 GRP rebar were used for four station passages in slurry wall construction on the first phase of the Dubai Rapid Link (DURL) metro. These required nine ‘soft eye’ structures in all. The rebars are easily cut by the TBM.
With concerns about the sustainability and environmental effects of concrete construction, especially carbon dioxide emissions, there has been greater interest in special blended concrete mixes. The use of pozalans, as specially manufactured, natural or by-products from other processes, can reduce carbon dioxide emissions, improve performances and lower cost. These advantages may have to be balanced against concerns about fresh concrete behaviour, rate of gain in properties such as strength and durability in extremes of weather. As a manufactured material and a by-product from silicon and ferrosilicon processes Elkem Microsilica from Elkem Materials can be used to increase strength and impermeability of concrete. Many ternary blends employ Microsilica together with fly ash and ground granulated blast-furnace slag (GGBS) in the blended mix, to combine the high performance of Microsilica with cheaper, more available supplementary cementing materials with drawbacks such as slower performance rate increases. T&T
Concrete casting Multiple concrete placement tasks were carried out in the underground Kopps II power station using a Putzmeister stationary boom MX 284 with a ‘Z’-fold system and fed alternately by two columns. Concrete placement The Kopps power station columns were fed by a PM BSA 1408 E trailer pump is the access tunnel through, and loaded by mixer trucks Trailer pump Ceresola’s invert shuttering currently being used in the Zurich Weinberg Tunnel for SBB Invert shuttering Doka formwork being used on the Steinhaus Tunnel Steinhaus Tunnel The Doka formwork used for the Adelrain Fork section of the Lötschberg Tunnel at Frutigen by SATCO Lötschberg Tunnel
