Construction of Flyovers
By Aravind Babu S.R, 3rd Year, Civil Engineering
Ever since my childhood it has always been fun to pass over a bridge. It is so much fun that I can’t even express myself with words. The joy we have experienced while passing the bridge may last for some minutes but constructing a flyover/bridge may take years. In this episode let’s look at how things are practiced on-field. This is a vast topic but let me try to make this the shortest possible.
Okay now before all the process begins the necessary details like the coordinates are marked by using survey equipment . As soon as this process gets done the road is ready to get expanded by relocating the utilities. The purpose of this expansion is to make sure that the road users are comfortable at all times. Then according to the readings / data/measurements the officials /engineers plan to raise piers by proper excavation, cutting and filling etc. Accordingly the pile is driven and reinforced with concrete. After piling pile caps are constructed. The depth of the pile cap varies according to the diameter of the pile driven. Then after pile caps are casted with proper reinforcement the pier is raised by shuttering .
The image below is a raised pier installed with proper formwork. In this case this is called scaffolding and this process is also called staging. This bone-like platform is used to help the labourers to work efficiently. Here a pier cap is already installed. Pier cap is something that is placed right above the pillar / column. The image on the right hand side is the stage before installing a pier cap. In this case pier caps are mostly casted on-site; they are not pre-fabricated.
While this is being done a lot of other works move on parallelly like elevation of low level roads to flyovers, drainage assembly, raising of electric poles to ensure safety etc.
The picture above is a compacted road, here in this case it is levelled up till the base course above this layer asphalt is placed properly. In the above picture you can notice the electric poles being raised so that the locals can use electricity without any hassle. Also both the roads are not compacted at the same time, they are done alternatively so that traffic can be avoided and when the compacted road is laid with asphalt it is ready to be used. After all this the other half of the road is also done in a similar manner .
After a solid compaction of the base course now the process of spraying lubricants begins. Usually spraying of bitumen is done and to achieve this the sprayers are fitted behind a heavy vehicle .
A series of spraying is done before laying the tar/asphalt. After this process the paver is brought to the site and the work of laying asphalt begins.
Now when this happens on one side the engineers also make sure that other utilities like landline cables, drainage slabs are properly installed .
In the picture above you can see a transit mixer /concrete mixer transferring concrete to install a drainage channel with a slab on top of it. After this the concrete is compacted manually by the labourers.
The picture above is a step previous to the above one. After this process the slabs are installed, here you can see the reinforcements clearly, after this they are properly shuttered and casted with concrete on site.
Now after all these processes service roads / frontage roads / exits are installed so that the vehicles passing over the flyovers can get access to the utilities available below.
As you can see the above picture is shuttered and reinforced properly to construct the service road/ frontage roads. Here many wet mats are covered over the casted concrete, it is done for the purpose of curing, in simple words it is done to prevent dryness.
Now it’s time for the most interesting part. So far we have seen how things go on ground surfaces. Now let’s get a little bit higher, let us look into the elevated part of the flyovers .
After the insertion of pier caps usually pedestals, bearings and PSC girders are installed in sequence. In this case I haven’t noticed any PSC girders on site. This bridge is a different form of segmental bridge, this one is considered to be more efficient and time saving one when traffic is concerned .
In the above image you can see segments being carried by heavy trucks and machinery. These segments are Pre-casted and brought to site, they are done in large numbers in order to finish the work as soon as possible. The image below is a clearer one for your reference.
Now let’s see how these are fitted above the pedestals. Notice the top left corner where you can see some reinforcements, they are done to cast the pedestals .These segments are lifted with the help of hydraulic machinery. They are mostly done at night times to ensure safety and hassle free work. Here you can see some holes also in the segment, they are called tendons where several numbers of steel rods are inserted inside each holes, generally 19 steel rods are installed inside and post tensioning is continued to ensure stability of the series of segments .
In the above images you can see a “Launcher Gantry ” this red- colored machinery is the hero of such similar projects. With the help of a hydraulic jack and railing system the segments are installed. This happens in sequence and the launcher keeps moving with the help of railing and trolley systems. This is a very long process and a very hectic one too. The above information may consist only 40 -50 % of the actual work. There’s a lot of work on -site like lot of manpower, machinery and other such resources are put into such projects. It is still disheartening to see bills/posters stuck on the piers/columns. The purpose of sticking posters was to pass on the message, where there was no means of communication but nowadays sticking posters is a pride. The above content is scripted to the best of my knowledge.
HOPE THIS WAS INFORMATIVE !
SEE YOU ON THE NEXT ONE !