About DF SkyWay - Engineering Concept

About DF Skyway

The Engineering Concept

HCC has used highly innovative engineering for the construction of the dfskyway™ Every process has involved careful planning followed by superior execution.

Actual Construction Sequence:-

Pilling was carried out by hydraulic rigs. Two types of piles were used to build a firm foundation for the 4.4 km. Elevated Highway i.e. friction piles with a 1,200 mm. diameter and end bearing piles with a 1,500 mm diametre.
Process of Pilling Work
Coordination of the piles was calculated from alignment drawings and marked with precise surveying equipment at the pier location
The pilling rig was brought into position to bore the pile
All loose material and muck was removed using Bentonite Slurry Flushing
The reinforcement cage was lowered into the bored pile and then the trimmie pipe was lowered.
Concreting was done in a way that ensured no slurry or voids remained while concreting the pile cap.

Pile Cap: In order to transfer load safely onto the piles, the pile cap was provided at the top of the Group of Piles.
Process of Pile Cap Casting
Excavation below ground as per the dimensions of the pile cap
Cutting of a 0.7 m pile head
Providing a PCC course to create a firm platform
Providing reinforcement as per the design & drawing of the pile cap
Erection of the shuttering & supporting platform to carry concreting
Concreting of the pile cap

Pier & Pier Cap: The pier and pier cap were provided to transfer the load of the superstructure to the foundation. Special moulds were fabricated to case the pier & pier cap monolithically, which reduced the time cycle by up to 4 days.
Process of Pier Casting:-
Reinforcement was provided as per the design & drawing
The shutting/mould was erected as per the required height of the pier
The pier start-up of around 100 – 500 mm. was cast to match the shutter as per the required height
The remaining height of the pier and pier cap was cast in a single pore with the help of the boom placer
After gaining sufficient strength, the mould was removed

Innovative Engineering:The innovative shutter design was implemented for both the pier and pier cap, which made it possible to cast both in one pour. This type of self-supporting shutter decreased the cycle time from 15 days to 3 days, which in turn led to early completion of the project. This process also left the cast piers with a slim design and provided for wonderful aesthetics.

Segmental construction was used in order to save time and money. The super-structure was composed of 2091 pre-cast segments that were cast at the casting yard using the Long Line method.
Process of Segment Casting:-
Setting out and surveying
Casting mould erection
Making and fixing of reinforcement cage
Positioning and fixing duct for the pre-stressing cables
Lowering of the reinforcement cage in moulds
Survey check
De-shuttering and curing
Sequence of segment casting
Lifting & storing in the storage bay and curing

Generally, the superstructure of the elevated highway is cast keeping the bottom level parallel to the ground and the cross slope adjusted in the top deck. But in Badarpur, the soffit too, has the same cross slope as the top, thereby giving the overall structure an elegant look while reducing the required concrete and steel. In order to achieve this, a special mould, which can be positioned in all three dimensions, was designed by a Swiss designer. This method also requires the very precise detailing of each and every segment before casting.
The pre-cast segments were transported to the site and erected with the help of the launching girder. For erection at curved locations, a trestle arrangement was used.
Process Segment Erection:-
Segment lifting, shifting & positioning on LG
Dry matching
Gluing & temporary pre-stressing
Threading, bearing plate fixing & permanent stressing (4 pairs)

The RE Wall was designed and erected with pre-cast panels of different sizes. These pre-cast concrete panels were cast as per a design based on the proposed height of the RE Wall. This requires limited construction space and occupies less space than a conventional wall system.
Process RE Wall Erection:-
Provided a concrete leveling pad
Erected the panel as per the position and alignment of the drawing
Fly ash or soil was filled in between the erected RE Panels and compacted to not less than 95% of the MDD.
The flyash was filled and compacted in layers
A reinforcing geogrid was placed in a position perpendicular to the RE Panels, folded at panel face, passed through the embedded connector rod and held in position with a cross insert rod.
It was then backfilled to the full height of the half-panels and compacted
After backfilling and compaction, the GSB, WMM, DBM and BC are laid to provide the approach to the elevated highway.

The construction of 40,000 sq. metres of RE Wall required 3.1 lakh cu.m. of earthwork. However, in Badarpur, we used fly ash instead of earthwork to save our precious land. Fly ash is a waste product that is generated during the production of electricity in a thermal power plant. Fly ash, in its dry state, is very light and blows easily with the wind, resulting in respiratory problems and irritation in the eyes. Also, no vegetation can grow in an area where fly ash is dumped. The use of this fly ash in the embankment filling saved a lot of land area and precious soil.