Larger tunnelling projects requiring substantial amounts of concrete, whether sprayed or cast in situ, will need their own batching plants on or near the surface working site. There have even been instances of batching underground, but the raw ingredients will still need delivery. The mixes may be required for sprayed concrete (primary or permanent) support, grouting. Even when most support lining is provided by pre-cast elements, there will still be a need for cement mixes to fill the annular gap, for concreting non-standard structures, and perhaps for injection grouting and a final lining. Whatever the requirement, the batching operations will need to be capable of producing the amounts required on time, and have the versatility for mix adjustment to suit, perhaps changing, requirements.
Compact plant
Even if the tunnelling project is fortunate enough to have plenty of room in the working site, a compact, modular batching plant may still be preferable to reduce transport and erection requirements.
The use of NATM in the construction of the 11.7-mile (18.8km) Phase 1 of the GBP 3.31bn (USD 5.25bn) Dulles Corridor Metrorail Project in Washington DC involves the use of a special dense sprayed concrete mix including microsilica and steel fibres. Preparation of the mix necessitated a mixing plant with a small footprint, since limited space was available, for which a Liebherr Easymix 1.0 plant was used. This is containerised to include most of the components in one assembly: mixing system, aggregate bins, water tank and microprocessor-based control room. The mix weighing equipment and cement feed are transported separately. With a steel base to the container, no separate foundation construction is necessary, but the plant was enclosed for winter protection.
The main mixer is a standard 1m3 ring pan mixer, with 48kW drive, but with the addition of a rotary agitator to better ensure a consistently high quality mix. The fine microsilica is stored in a special silo with its own screw discharge and weigher. Steel fibres are also added at this point using a vibration bowl and belt conveyor delivery to the mixer. Another additive is a retarder to ensure a 3-hour mix workability life before application.
The mix control is achieved with a Liebherr Litronic BCSII computerized system including a Litronic FMS-II moisture controller. The output of the plant is about 30m3/h (109m3/day) with a batch cycle time of two minutes; plenty for the project’s requirements. The plant’s pan mixer discharges onto a belt conveyor and thence into special lowprofile truck mixers to go into the tunnel. Construction started in March 2009 and is scheduled to finish in 2013.
Another Liebherr Easymix 1.0 is being used by Vegas Tunnel Constructors (joint venture of Healy and Impregilo) for the Lap Take No. 3 Tunnel Project in Nevada, US for Las Vegas water supply. The plant again supplies fibre-reinforced sprayed concrete plus annular grout for the tunnel to be lined with precast liner rings, and standard concrete for foundations. The plant is configured to supply spraying concrete very quickly through 24 hours.
For England’s A3 Hindhead Tunnel, contractor Balfour Beatty employed a Liebherr Mobile 90 batching plant to produce sprayed concretemix for a composite-type support and waterproofing lining.
Grout and more
Team Mixing Technologies (TMT) of Canada tends to concentrate on plants to produce grout and backfill mixes, chiefly for the mining market, but has also supplied some major tunnelling products such as the Brisbane Airport Link. The company’s list of supplies includes materials handling systems, electrical and control systems, and dust control measures as well as the basic batching plants.
In western Venezuela, TMT supplied 60m3/h concrete batching plants for both ends of the 24km-long Estrada Lara irrigation tunnel. The tunnel is to supply water from the lush Yacambu valley to the desert area in the neighbouring Quibor valley. The plant products are both concrete for spraying and for cast lining. The plants feature 4-yd3 (3.1-m3) Voelier pan mixer and is plc controlled. TMT carried out all functions from design to commissioning and training. Other features of the plants include aggregate storage bins, three cement silos each with screw conveyors, weigh hopper, dust collection system, belt conveyors and controls.
For the Thiess-John Holland joint venture on the Brisbane Airport Link TMT designed fabricated and equipped two, fully automated, 2-component grout plants of 23m3/h capacity for annular gap filling around the two Herrenknecht EPB TBMs over 15km of tunnelling at 12.45m diameter. As with other TMT grout plants, the system features the company’s highshear colloidal mill mixers for maximum grout strength with minimal ‘bleed’. Highpressure Elepon ETK peristaltic pumps are used to transfer grout and accelerator to holding tanks on the TBM back-up systems. TMT also undertook on-site training and service support.
CIFA’s (part of the Zoomlion group) range of concrete batching and mixing plants include both dry and wet work. The wet line has both horizontal and vertical concrete plants, the latter suiting limited space availability. These include the Cifamix units, whilst Turbomix and Rotomix double horizontal shaft concrete mixers have outputs of batched concrete up to 4m3. The dry process range come in Compact, Personal and Dual models with outputs of 40-150m3/h. Aggregate storage capacities are up to 300m3.
Tunnel projects that have been supplied with batching plants by Sinem of Italy include the Mont Blanc Tunnel post-fire reconstruction, and the Kurichu Dam and Tala hydroelectric projects in Bhutan. The Sinem Wetbeton range is modular in design to reduce site erection and assembly times to no more than ten days, and without any welding.
For the Mont Blanc project Calcestruzzi of the Italcement Group used a single Wetbeton 120 plant for the supply of sprayed concrete and cast structural concrete. The work demanded concrete batching work 24h/day over 15 months.
The Wetbeton 120 model was also used by Hindustan Construction Company (HCC) in Bhutan for the Kurichu and Tala dams and the Tala headrace tunnel. Production was up to 100m3/h using aggregates up to 120mm in size, plus flaked ICE and chilled water for concrete cooling in the dams.
Adler Technologies of France offers horizontal, semi-vertical or vertical concrete batching plants with capacities of 10-60m3/h. Storage capacities are included according to client specifications in the ranges of 40-700t for aggregates and 30-100t in silos. Adler uses various mixing technologies but has developed the vortex principle in mixers in which the cement mixture is suspended whilst aggregates are propelled upwards into it. This is claimed to reduce cycle time, optimise mix quality, and reduce cement consumption. Other types of mixing used are turbo, planetary and horizontal shaft. Dedicated automatic control systems for batching plants are available.
Truck to place
If the tunnel project has a relatively low concrete requirement, due to its dimensions or self-standing support, then it is possible to meet all concrete requirements by mixer-truck ‘ready mix’ concrete, particularly if the site is within economic travelling distance of a commercial general batching plant. In tunnels of sufficiently large section the mixer-trucks may enter the tunnel itself to carry the concrete to the area required.
CIFA’s latest truck mixer addition to a wide range is the HD 12+, which, on a 4- axle carrier with a capacity of over 45t, is designed for heavy-duty applications including payload capacity of over 12m3. It features a thick-section drum and blades, double rollers with sling bar for improved off-road support, and an anti-rebound device. The discharge chute and charging hopper have wear plates, and the chute is hydraulically driven from a manual pump with adjustable support. The discharge chute can optionally be shaped to a cone with a 200mm-diameter hose extension. An on-board water tank, pressurised if required, is another option.
The compact Liebherr Easymix 1.0 batching plant used to produce reinforced sprayed concrete for the Washington Dulles Corridor Metrorail Project, US, includes many components in one standard container Another Liebherr Easymix 1.0 is used at the Lake Mead No. 3 tap tunnel project by Vegas Tunnel Constructors. Here is occupies a small footprint (left centre) within the working shaft site; CIFA’s latest heavy-duty truck mixer, the HD12+
