What is Tunnel Form and its usage in Construction

What is Tunnel Form and its usage in Construction

Form work is one of the most important factors in determining the finished appearance of in situ construction, strength & durability of the structure. Yet the role of the form work and the choice of the correct form work system have been subjects neglected in the construction industry. Today the trend in the construction industry is towards reduced construction time and cost, improved work place safety and standardization. In the recent past, the incidents of natural calamities like earth quake etc have become were frequent. The quick re-habilitations of the victims is a long challenge being faced by most of the countries.

To catch the above trends, it is imperative to develop form work systems which are productive, quick and easy to erect, quick and easy to strike, reusable at least more than 100 times and cost effective, tunnel form system is one of the such systems. This is a method in which the walls and the slab in a single operation with collapsible ensuring easy workability. In this system the construction time is much shorter than the conventional methods. Several studies shows that almost 50% of the time is saved compared to additional methods for completion of the project thereby reducing overall cost and risk of prolongation of duration.

- Fast construction fits to tight construction schedule.
- One set of tunnel form can provide a for half day cycle in place of 20-25 days cycle with conventional methods.
- Saving through reduced construction time. No effect of price hike
- Shuttering may be stripped after 12 hours of the concreting
- A monolithic structure, which needs the requirements of building codes of the countries/ area located in earth quack zones.
- Form work strength of 5.5 t/ Sqm. At normal pouring rates.
- A nice concrete surface that eliminates much of the finishing work like plastering
- A prefect daily rhythm for the other operation at site
- Dimensional accuracy that allows pre-fabrication of finishing material.
- Complete work place safety

The tunnel form is placed in position with the help of a tower crane to half shells which are placed together to form a room or a cell, while several shells are making an apartment. After placing two tunnel forms together, the level can be adjusted with the help of its leg jacks and wheel strut. The soffit level can be adjusted with the inclined prop. The two adjoining room tunnel forms are tied together with the help of tie rods. To fix the tie rods, a spacer cone is provided between the vertical panel of two tunnels & the tie bolt pass through this cone. At the gable end of the building gable end frame is erected to support the outer wall to form strong back. The global end frame is specially designed frame to support end form & it can be installed within no time. for sidewalks & to facilitate stripping, stripping platforms are erected. The typical arrangement is given in the sketch

The next morning tunnels are ready for opening after testing of the cubes. The opening procedure is also very easy & can be solved very fast. In fact the opening of the tunnel on one floor & its mounting on the other floor can go on simultaneously. It saves lot of time. For this purpose all the insulating materials are removed, tie rod & nuts are removed and placed on horizontal walling. After opening of all ties, the leg jacks are lifted first and then a slight deformation is given to the half tunnel form by shortening the inclined struts. The half tunnel array will drop down automatically to the floor. After this the forms are manually rolled out onto the stripping platform and the lifting triangle is attached by securing the wing nut of the triangle. Than the form are placed to next location. All spacer cones re removed from the wall by means of a punch.

- The wall thickness is reduced
- Dead load of structure reduced
- Monolithic construction
- Smooth finish
- Reduced construction time

- Fits in modular construction
- Building should be so planned that max tunnel from can be done with the help of one location of tower crane.