Tunnel Form Technology

GEM has been appointed as a project manager by one of the reputed developers in India, at their project in Pune wherein tunnel formwork system is being used. This is our first experience with the Tunnel form technology. The project has a built-up area of 13.83 lakhs sq.ft. in (Phase 1) out of which about 10 lakhs sq.ft. built-up area will be made using tunnel form. RCC part of each of the 22 story buildings is planned to be completed in just 4 months with half set of formworks. The tunnel forms can thus be released and be available for Phase 2 of the same project!
Tunnel form technology like any other new technology requires attention to many aspects and challenges of construction in a different manner than in conventional works. Some of these challenges may be:

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• The planning of the building should lend itself to the adoption of tunnel form technology. That is why the decision to use tunnel form should be taken even before the schematic of the building is finalized.
• Similarly, the tunnel form supplier should also be on board from an early stage so that their inputs to optimize cost of tunnel form can be incorporated in design if possible. In time delivery of tunnel forms can also be assured by having the vendor on board early.
• The number of flats (repetition) should be large enough to justify the higher capex on tunnel form.
• The concrete mix should be carefully designed to allow pouring all concrete in one pour and should have the right workability and early strength development.
• Other resources like tower crane, concrete batching and rebar handling and placement should match the speed afforded by tunnel form
• Trained manpower should be available to handle the tunnel form as it has more to do with assembly (mechanical work) than carpentry!
• The form work must be handled and maintained carefully else many of the advantages will evaporate.

At the same time, Tunnel form technology offers many advantages over conventional beam-column-slab construction which may overcome above mentioned challenges faced by designers, construction managers and contractors. Many of these advantages hold good even when it is compared with monolithic slab-wall type of construction using Aluform (popularly known as Mivan technology).
Major Advantages of Tunnel Form System:

• High seismic resistance due to monolithic slab & walls construction
• Monolithic structure reduces number of joints and improves water tightness
• Reduce labour costs (greater requirement of tower crane)
• Reduce mobilization costs on site
• Reduced construction times (2-3 days slab casting cycle can be achieved) which is up to 3 times faster than conventional
• Higher quality finishes &#;Fair faced finish concrete can be achieved
• No need for plastering

If the technology is adopted right from the planning and design stage, project costs savings up to 25% can be achieved.

Tunnel form is a formwork system that allows the casting of walls and slabs in one operation resulting in a cellular RCC structure. It combines speed, quality, and accuracy with the flexibility and economy of in-situ construction. The system creates an efficient load-bearing structure for use in a wide variety of applications. A tunnel form is a box-sized steel fabricated form that allows the wall and the slab to be cast in a single operation. The system creates an efficient concrete wall slab load-bearing structure for use in a wide variety of applications. The typical assembly of various elements of the tunnel formwork system. It is most suitable for mass housing & fast build projects which require more repetitions at a faster rate of building construction. While the initial cost of formwork is very high, it is more than made up by faster construction, the number of repetitions, zero rework, and low maintenance cost. Tunnel form has integral working platforms and edge protection systems. In addition, the repetitive, predictable nature of the tasks involved encourages familiarity with operations, and, once training is complete, productivity improves as construction progresses. The minimal requirement for tools and equipment when moving the tunnel form further reduces the risk of accidents on site.

Advantages of tunnel form

Tunnel form technology offers many advantages over conventional beam-column-slab construction. Its major advantages are;

• Collapsible strut provides clearance for form stripping
• The composite wheel assemblies help in accurate form positioning and blackouts eliminate nailing
• Multiple rooms can be concreted and that provides flexibility in scheduling.
• Tunnel form can be adapted to special building features, like balconies.
• Allows variety in architectural designing
• The dimensional accuracy of the concrete structure allows the placement of partition walls and fixing of all other finishing material such as joinery right after casting
• Standard push-pull props can be used at every tunnel dimension due to their telescopic nature and make it very easy to adjust vertical and horizontal leveling.
• Installation of all utility conduits in the shell reduces the internal finishing work
• Tunnel formwork required less slab cycle time due to that construction becomes fast and reliable
• Construction of box-type structure is safe against horizontal forces like earthquake and cyclone forces
• Tunnel formwork is available in half units in the shape of an inverted L
• Ensures correct application and completion of the project by minimizing measurement errors during the production process
• Comes with integral working platforms and an edge protection system
• High seismic resistance due to monolithic slab & walls construction
• The monolithic structure reduces the number of joints and improves water tightness
• Reduce labour costs
• Reduce mobilization costs on site
• Reduced construction times which is up to 3 times faster than conventional
• Higher quality finishes &#;Fair faced finish concrete can be achieved
• No need for plastering
• The in situ casting of units on-site and the local availability of ready-mixed concrete supplies reduce transportation impacts

How does tunnel form work?

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The cycle time of the tunnel formwork system lies between 1 to 3 days, which is very little compared to other formwork systems. So tunnel formwork took a lead in the time-saving of projects which indirectly affect the total project cost.

Slab cycle time involves the following activities

• Wall shuttering
• Slab shuttering
• Slab level
• Leveling
• Line and plumb
• Wall reinforcement
• Slab reinforcement
• Electrical fitting
• Casting of slab
• De shuttering wall
• De shuttering slab

Tunnel formwork is a mechanized system for cellular structures. It is based on two half-shells that are placed together to form a room or cell. Several cells make an apartment. With tunnel forms, walls and slab are cast in a single day. The structure is divided into phases. Each phase consists of a section of the structure that will be cast in one day. The phasing is determined by the program and the amount of floor area that can be poured in one day. The formwork is set up for the day&#;s pour in the morning. The reinforcement and services are positioned and concrete is poured in the afternoon. Once reinforcement is placed, concrete for walls and slabs shall be poured in one single operation. The formwork is stripped in the early morning and positioned for the subsequent phase. The formwork is manufactured in a fully automated plant.

1. Stripping of the formwork from the previous day.
2. Positioning of the formwork for the current day&#;s phase, with the installation of mechanical, electrical and plumbing services.
3. Installation of reinforcement in the walls and slabs.
4. Concreting and if necessary, the heating equipment.

When is tunnel form suitable?

Tunnel form is widely used in the construction of cellular structures with a high degree of repetition such as:

• Prisons
• Hotels
• Student Accommodation (Hostels)
• Private Housings
• Commercial Developments

Conclusion

Tunnel form is a formwork system that facilitates the casting of walls and slabs in one operation. It not only enhances the accuracy of concrete construction but also helps create efficient load-bearing structures that are known to be earthquake-resistant and can be used in a wide variety of applications. Additionally, this technique helps to save finishing cost to a great extent. The surface of the reinforced structure requires minimal finishing, and the structure is particularly effective in the construction of residential blocks, hotels, student accommodation, barracks, and prisons.

If you want to learn more, please visit our website steel formwork trolley for tunnel and highway construction.