The Metro viaduct between the South Campus and Delhi Cantt Metro Stations of the under construction 59 km long Majlis Park- Shiv Vihar corridor of Delhi Metro's Phase 3 which will cross over the existing alignment of the Airport Express line at Dhaula Kuan will be a major engineering achievement for the Delhi Metro Rail Corporation (DMRC), as the viaduct will be constructed without hampering movement of trains on the Airport Line and the road traffic movement (Ring Road - Sardar Patel Marg) below.
The height of the viaduct will be 23.6 mtrs at this spot (as high as a 7 storey building) and will be the highest point of Delhi Metro so far surpassing Karkarduma where the Metro is 19 mtrs above the ground.
The launching operation above the Airport line is being done only during the non-operating hours (i.e between 12.30 AM till 4AM) to avoid any disruption to the traffic on Airport line.
During this time, no activities for train operations are permitted on that portion of the Airport Express Line. Launching work starts only after getting all clearances from Operation and Maintenances (OandM) Department of the Airport line. All the parts of launcher are earthened before commencing the work. A diversion road has also been constructed so that there is no inconvenience to the road users during erection.
In order to ensure the safety of the workers and the trains and traffic below, the DMRC has installed CCTV cameras at various locations on the viaduct of the Airport Line and on the launcher to monitor the overall activities. A team of six civil engineers, two safety experts, the engineers from OandM department and other experts are closely monitoring every movement of launching in the night so as to ensure that process of erecting segments over the existing viaduct and OHE of the Airport Express line is carried out smoothly without causing any inconvenience/damage to the already operational line.
The design team of DMRC also prepared the design of the viaduct after closely studying the requirement of passing over so many major landmarks such as the Airport Line viaduct and the flyover at such a height.
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Three spans of 37 metres and are being made by segmental box girder by the launcher. A span of 37 metres, has 13 segments weighing 45 tons each on an average which means each span of 37 metres has a weight of 585 tons and weight of the launcher is 350 tons.
Difference between the rail levels of this under construction line and existing Airport Express line is 11.90 metres,. The viaduct of the Airport Express Line is at a height of 11.7 metres from the ground level.
This under construction viaduct above the Airport express line, flyover (Sardar Patel Marg) and slip roads is 111 metres, long and is supported by 4 piers of 23.6 metres height. This viaduct will be completed by the end of October 2014 as during one block only one segment can be erected.
Apart from Dhaula Kuan, the elevated viaducts of Delhi Metro's Phase 3 will pass over the existing viaducts of the Phase 1 and Phase 2 Metro corridors at four more different locations. These are: Karkarduma, Netaji Subhas Place, Mayur Vihar and Anand Vihar.
Due to close proximity with the existing flyover and Airport line viaduct, and as the segments are to be lifted to a height of about 23 metres, a systematic methodology has been planned for the erection of the segments.
The segments are being erected through a special four step method because of the extra height involved.
In the first step, the trailer brings the segment and parks between the already constructed piers.
In the second step, the segment is lifted by extended winch assembly having a load carrying capacity of 120 T, where as the maximum weight of any segment is 55 T and transfer of the same to the extended Macalloy bars extended by couplers as the normal arrangement of winch and Macalloy bars fixed to a slider can launch the segment only up to 15m height. Then the segment is to be transferred to normal winch assembly and extended macalloy bar is to be removed and again lifted to height so that it is transferred to macalloy bars fixed to slider.
In the third step, the segment is rotated and is attached with segment trolley/ slider using four numbers of 40 mm dia Macalloy bars having a capacity of 129 T. Additional safety has also been provided by way of two slings of adequate capacity along with 4 Macalloy bars fixed to sliders.
In the fourth step, the segment trolley/slider is pushed to one end of the pier where it is to be erected, through segment launcher.
Then the gluing of the segments is carried out followed by stressing.