REPORT ON TUNNEL

SUBMITTED TO:- PREPARED BY:- Brig. S.K. Sharma(Retd.) Nitesh Chowdhry (12CVU033) Shivam Sharma (12CVU043) Deepanshu Goel (12CVU017) INDEX S.NO TITLE PAGE NO. 1 INTRODUCTION 3 2 HISTORY 5 3 COMPONENTS 6 4 CONSTRUCTIO 8 N SEQUENCE 5 ADVANTAGE 9 6 SUMMARY 10 7 REFERENCES 11 INTRODUCTION

Slip forming, is a method in which is poured into a continuously moving form. Slip forming is used for tall structures (such as bridges, towers, buildings, and dams), as well as horizontal structures, such as roadways. Slip forming enables continuous, non-interrupted, cast-in-place "flawless" (i.e. no joints) concrete structures which have superior performance characteristics to piecewise construction using discrete form elements. Slip forming relies on the quick-setting , and requires a balance between quick-setting capacity and workability. Concrete needs to be workable enough to be placed into the form and consolidated (via vibration), yet quick-setting enough to emerge from the form with strength. This strength is needed because the freshly set concrete must not only permit the form to "slip" by the concrete without disturbing it, but also support the pressure of the new concrete as well as resist collapse caused by the vibration of the compaction machinery.

In Vertical Slip forming the concrete form may be surrounded by a platform on which workers stand, placing steel reinforcing rods into the concrete and ensuring a smooth pour. Together, the concrete form and working platform are raised by means of hydraulic jacks. Generally, the slip form rises at a rate which permits the concrete to harden by the time it emerges from the bottom of the form.

In Horizontal Slip forming for pavement and traffic separation walls concrete is laid down, vibrated, worked, and settled in place while the form itself slowly moves ahead. This method was initially devised and utilized in Interstate Highway construction initiated by the Eisenhower administration during the 1950s.

HISTORY

The slip forming technique was in use by the early 20th century for building silos and grain elevators. James Macdonald, of Macdonald Engineering of Chicago was the pioneer in utilizing slip form concrete for construction. His concept of placing circular bins in clusters was patented, with photographs and illustrations, contained in a 1907 book, “The Design Of Walls, Bins, And Grain Elevators”. In 1910, Macdonald published a paper “Moving Forms for Storage Bins,” describing the use of molds for moving forms, using jacks and concrete to form a continuous structure without joints or seams. This paper details the concept and procedure for creating slip form concrete structures. On May 24, 1917, a patent was issued to James Macdonald of Chicago, "for a device to move and elevate a concrete form in a vertical plane". The technique was introduced to residential and commercial buildings in the late 1960s. One of Its first uses in high-rise buildings the United States was on the shear wall supported apartment building at Turk & Eddy Streets in San Francisco, CA, in 1962, built by the San Francisco office of Macdonald Engineering. The first notable use of the method in a residential/retail business was the in Niagara Falls , Ontario, which was completed in 1965. Another unusual structure was the tapered buttress structures for the Sheraton Waikiki Hotel in Honolulu, Hawaii, in 1969. Another shear wall supported structure was the Casa Del Mar Condominium on Key Biscayne, Miami, FL in 1970. From the 1960s, the vertical technique was adapted to mining head frames, ventilation structures, below grade shaft lining, and coal train loading silos; theme and communication tower construction; high rise office building cores; shear wall supported apartment buildings; tapered stacks and hydro intake structures, etc. It is used for structures which would otherwise not be possible, such as the separate legs of the Troll A deep sea oil drilling platform which stands on the sea floor in water about 1000 feet (300 m) deep. COMPONENTS OF SLIPFORM

A slipform assembly can only start after the foundations of the walls have been correctly laid and a starter for the walls laid out in its correct alignment with all the necessary steel for the walls already in position. The slipform shuttering is then firmly aligned to this starter with the means of yokes on each side of the shuttering that help to keep the panels in position. The yokes are all connected by horizontal crossbeams. Hydraulic jacks are then installed rigidly to the crossbeams that can all act simultaneously so that the entire slipform shuttering moves upwards. The heights of such slipform shuttering will normally be between 1.1 meters to 1.5 meters in height. The yokes and horizontal crossbeams are also used to support a working platform that can afford space for men and materials. The jacks climb using jacking rods that are installed within the concrete and become a permanent part of the structure, or can be retrieved if so desired. The design of the working deck and the yokes and horizontal crossbeams are a very vital part of efficient slipform construction. It is very important that the entire structure be such that its rigidity and shape is maintained at all times. It is quite normal for the two sides of the shuttering to be inclined towards each other at the top with the correct wall dimension available at the center. This allows the shuttering to move easily and eliminates any drag that concrete can cause on the shutters to prevent its free upward movement. The rigidity of the supporting platform is also essential so that all parts of the structure move simultaneously. If there is any lag from one part to the other, this can cause the shuttering to drag and make it difficult to be pulled up. It is also possible to reduce wall thicknesses as the construction gains height and arrangements have to be made in the slipform structure that will enable such reduction at regular intervals.

Once the slipform shutters along with the jacks and support deck are in position, concreting operations can then commence. Sufficient working space has to be created on the deck to accommodate reinforcement bar activity. The bars have to be continually lengthened and placed in position as per the structural requirements for the wall. The concrete is poured in layers, and by the time the concrete level has reached the top, the concrete at a level 300 mm above the bottom of the panel should have gained the initial set. The rate of pouring of the concrete has to be adjusted so that this is achieved. The slipform is then moved upwards in steps of 10 mm to 25 mm and both the concreting and placing of the reinforcement bars is done continuously till the final height is reached. All jacks are fitted with brakes that act automatically by mechanical means and do not allow the jacks to slip on the jack rods. CONSTRUCTION SEQUENCE

1. The formwork and the access platform are assembled on the ground.

2. The assembly is raised using hydraulic jacks which are mounted on strategically located steel frames to lift the formwork as the concrete is poured into the forms.

3. As the formwork rises continuously, continuous concrete and supply are needed until the operation is finished. 4. As the formwork is raised, reinforcement is held in the correct position using guides, horizontal reinforcement is tied to the vertical reinforcement.

5. Concrete is poured into the forms in layers of approximately 200 mm. The setting rates of concrete are constantly monitored to ensure that it is matched with the speed at which the forms are raised. The jacks lift the form approximately 25mm per stroke generally producing a slip-forming rate of 300 mm per hour

6. Slipforming can be performed on either a continuous basis (i.e. 24 hours per day), or a discontinuous basis (i.e. pouring to a predetermined height usually within one working day) .

7. Block outs for doors and windows can be formed with either timber or steel. These are in-stalled as the slipform proceeds and can be stripped from the trailing decks .

8. Recesses are made to host the connections between the beams, slabs and the slipform walls.

9. When the formed concrete is exposed from the bottom of the steel form panels it can be sponged or treated if required .

10. At the end of the operation the formwork is removed using a crane, the entire process is thoroughly inspected and highly controlled Slip forming relies on the quick-setting properties of concrete, and requires a balance between quick-setting capacity and workability. Concrete needs to be workable enough to be placed into the form and consolidated via vibration. This strength is needed because the freshly set concrete must not only permit the form to "slip" passed the concrete without disturbing it, but also support the pressure of the new concrete as well as resist collapse caused by the vibration of the compaction machinery. ADVANTAGES OF SLIPFORM

• A major cost of concrete structure construction comes in the form of the required formwork to retain the concrete while it retains it necessary shape and gains the necessary strength till it can be safely de-shuttered and be able to support itself and other imposed loads. • This greatly reduces the cost of the formwork as well as any time that may be required to erect and move it for re-erection, which can result in huge savings in time as well as money. • The continuous operations also allow for an evening-out of the manpower requirements and also a huge saving in the labor that may have to be periodically employed during otherwise intermittent concreting operations. • The reduction in the movement of formwork and workers also leads to far more safe working conditions that also make it a major advantage.

• The slipform setup provides a safe and protected work environment for your crew. Relatively little climbing is required, the work area is compact and unchanging and weather protection can easily be added to the formwork setup. Enclosed spaces can be heated during the cold weather periods.

• Slipform is never released from the structure during climbing, as is commonly done with other form systems. It only climbs in small increments and is continuously connected to the structure at multiple points, making it a very safe system. SUMMARY