As mentioned in the previous article, highway legal truck mixers can be used to deliver concrete and grout mixes to near the point of use in a tunnel, providing the dimensions allow it. There are also more compact specialist vehicles, more suited to tunnel conditions, but of normally lower capacity. However, in most large tunneling projects with long drives, rail transport is employed to deliver materials. The frequently large volumes of concrete employed, particularly for permanent cast in situ lining, require high capacity vehicles.
Rail cars
Rail transport specialist Muhlhauser (KHM) offers a wide range of rolling stock for concrete and ingredients transport including both standard and custom-made designs. Standard Muhlhauser concrete remixer cars, with longitudinal axis rotation, have electrohydrostatic drives and a range of capacities from one to 14m3. For greater requirements, up to five cars can be used in series together in a train, one feeding the next up until the discharge point. Recent applications have been for the Gotthard Tunnel (TAT consortium) and the Brenner Tunnel. Mortar containers (portable boxes or cars) are made with internal auger mixers with electric, hydraulic or pneumatic drives. Recent applications have included the Finnetunnel, Denmark (17m3 mortar car), SMART project in Kuala Lumpar, Malaysia (20m3 mortar car), La Cabrera Project, Argentina (11m3 mortar box, and Barcelona Metro Line 9 (6m3 mortar box).
An alternative is the transport of dry mix ingredients using silo cars with discharge devices such as horizontal screw or belt conveyors, or gravity feed chutes. The latter can have manual or automatic actuation of closure flaps. Muhlhauser says that all components are oversized long operating periods and life.
Trackless
Dedicated trackless concrete transport vehicles from Normet Utimec range in capacity from 4.4 to 5.6m3. They are lower in height than highway truck mixers, but the different models have a range of features to suit the circumstances. The Utimec LF 600 Transmixer, for example, with a capacity of 4.4m3, has an available tractive effort of 190kN for steep inclines and rough ground. It also has smaller wheels for fast operation.
The Normet range also includes a transferable cassette system called Multimec, one cassette of which is a concrete remixer. Such a system can be used for intermittent concrete transport needs, but is most often found in mining applications. For greater needs, dedicated concrete transporters such as Normet’s Utimec Transmixers and agitators can be used. The larger Variomec MF 050 M concrete remixer is a part of another Normet interchangeable module system, but mounted on an articulated carrier. Other modules are available for rock hauling and an access boom man-lift.
Truck mixer delivery
Where the tunnel section is sufficiently large, and removed of major obstructions, to allow the highway-legal truck mixers, one still has to decide on how the concrete is to be transferred to the means of use. The same applies to specialist underground truck mixers and modules such as from the Normet and Muhlhauser ranges, including rail-mounted mixers in the latter.
In many cases, particularly in the case of sprayed concrete, the truck mixer chute can be simply sited over the reception hopper of the shotcreting equipment for direct use while keeping the mix agitated.
At the other extreme there may be no alternative to pumping the concrete for cast in situ placement, such as in order to ‘hose’ the concrete behind formwork shuttering, particularly at high levels.
Where they can be used, small belt conveyors offer a mid-way to concrete delivery. They are best suited to low level concrete delivery such as for invert lining, track beds and pavements. Limitations are that delivery has to be in a straight line and steep angles of delivery may result in material slump back. The mechanism is relatively simple, however, compared to concrete pumps.
The Liebherr range includes compact LTB belt conveyors that can be carried on top of truck mixers using folding belt heads. In the 4-model range, delivery radii vary from 11.5 to 16.2m. In all cases the output is around 70m3/h.
Pumped
The other major option for concrete transport in tunnels, particular through smaller sections, is pumping. Although perhaps not as versatile as wheeled transport to cover distance, pumping can also be used to go around angles quite easily, including placing concrete behind formwork, and at higher levels. Even so, pumping can reach substantial distances that can make its use feasible in many tunnels. For example Putzmeister claims a world distance record for concrete pumping of 2015m, achieved with a BSA 14000 HP-D pump on a site in France. A top pumping height of 532m using a pumping pressure of 18.5MPa (185bar) has also been achieved.
The Putzmeister range can be applied to most operations up to 220m3/h delivery and 40MPa (400bar) pressure. Finer (up to 32mm grain size) materials, such as grouts and shotcrete mixers, can be handled by small, high-pressure pumps with ‘S-tube’ technology. Grout mortar (grain sizes up to 8mm) can be pumped over particularly long distances using pumps with ball-valve technology, obtaining pressures up to 13MPa (130bar).
Although there are many suppliers of concrete pumps, including truck-mounted versions, there are few that offer the range of tunnelling specialist equipment presented by Putzmeister and CIFA. The main areas of difference are in boom reach and pipe articulation, but this is more a matter of placement covered in the next article. There are also special skid- and railmounted pumps such as Putzmeister’s RCU-702 Rail Concrete Unit.
When transporting concrete mix over long distances or great differences in height, whether by gravity, pumping or pneumatic conveying, attention has to be paid to the possibility of mix separation with a tendency to segregation of heavy aggregates from binding ingredients and water. In order to combat this pump design and operation can be coupled with the use of mix additives.
In cases of intermittent mix usage, some form of bunkering may be advantageous. Dedicated remixer cars and similar devices are their own bunkering. In pumping operations Putzmeister offers the Jumbo Trough JT5000, the basic design of which can be adapted to particular user needs. The standard design has several mixing spirals to homogenise the mix, thus helping to avoid segregation. Capacities range from 2 to 15m3.
CIFA’s latest mobile pump is the Series 8 Models 1007/712 with outputs of up to 100 and 65m3/h with respective maximum concrete pressures of 72 and 115bar. The low-noise, Deutz diesel-driven, trailermounted unit is designed for heavy-duty conditions. The main pump unit is of axial piston type for variable for capacity and constant power. The ‘S-shape’ valve fitted is suitable for any type of concrete. Components compensate automatically according to wear. Optional radio remote control is available.
Trains & shunting
A recent appearance of an Adler Technologies tunnel concreting train was the new Gotthard base-tunnel just before the first main breakthrough in October last year. It started concreting the beds for the first metres of rail track in the southern portion whilst tunnelling continued further north. Work commenced after several weeks of ‘real situation’ testing and validation overall length of several hundred metres. The train comprises 23 cars weighing a total of 1200t, and will be used to concrete the 57km of tunnel at a rate of 260m/day. Adler already supplied a similar train for the Channel Tunnel. Concrete batching train capacities range from 15 to 60m3/h for functions such as foundation bed and side structure placement and grout injection using onboard pumps or transfer cars.
An unusual means of moving concrete mix in tunnels is in the reported use of an ex-Swiss Army Mercedes Benz Unimog by contractor Marti in the Cassanawald Tunnel, Switzerland, last year. The Unimog can work on tracks due to road-rail attachments fitted by specialist company Zwiehoff by which it can negotiate gradesup to three per cent.
The 40m-long train, weighing about 60t, included a 19m-long ‘machine wagon’ carrying both wet and dry-process concrete sprayers. The second wagon carried a permanent concrete mixer, the third compressors, and the fourth materials silos. Protection screens against concrete bounce-back are provided for the Unimog and the machine wagon. The equipment was used to apply layers of fireproofing mortar.
A Normet Utimec low profile truck mixer emerging from a tunnel on Washington’s Dulles Metrorail Corridor project The largest of Dieci’s range of compact truck mixers – the F7000 with a capacity of 5m3 A concreting train on Malmo City Tunnel project carrying an electrically operated Putzmeister and mixer cars to lay a slab track system The new Series 8 Model 1007/712 trailer concrete pump to be launched by CIFA in April
