The DMRC architects and engineers, for the first time, completely redesigned the underground station, utilizing all three levels i.e. the Mezzanine, Concourse and Platform, to accommodate all the essential equipment, which are generally, placed only at Concourse and Platform levels of underground stations. This was done by reducing the length of the platform for relocating Ticket counters and Automatic Fare collection gates and shifting of Ancillary buildings and Ventilation Fan rooms vertically upwards. DMRC, thus, ensured that despite less space, the commuters got the same facilities and quality of service.
Less Space, More Scope to work
The Ashram underground station on line-7 of Phase-III Delhi Metro, was a typical underground station box of 265m length located along the Ring Road at the intersection of Mathura Road at the Ashram Chowk junction. The PWD had also proposed an underpass at Ashram Chowk, which was to be constructed in the future. So, keeping provision for this underpass, the rail level at the station was dipped to -20m below ground, so that in the future, the proposed underpass could be constructed above the station concourse level.
Planning and detailed design of the station was done, and construction was started. However, there was a private plot which was needed for the construction of a part of the station box; acquiring it was posing a problem for completion of the project. It may be noted that construction of the tunnel from Hazrat Nizamuddin was already complete at this stage and the TBM used was waiting to be retrieved. Therefore, the station box boundary shrank a little further.
Given the constraint of a flyover adjacent to one side of the station box being constructed, and CSIR apartments along the other side, there was no other option but to shift or relocate the station box. At this stage, it was decided that design options should be explored to contain the station box within the available space on site. This provided for an internal length of 151 metres for the new station box. After many deliberations, an alternate design for the underground station at Ashram was developed.
The design change was made after duly considering aspects related to changes in alignment, land requirement, systems design and structure design. The problem got further complicated due to the fact that half the diaphragm wall was already constructed as per the original design, thus, restricting the levels of slabs possible within the station box. The new design had to fit within the existing parameters of site constraints as well as the structural design.
Platform and the Interiors
The length of the platform for a typical 6-car train is 140 metres. At this station, the length of the platform was reduced to 135 metres, which is just enough to ensure clear 3 metres width in front of the passenger doors as well as the driver cabin door of the rolling stock. In addition, the center-line of the platform was shifted by 57 metres towards Hazrat Nizamuddin to keep the platform length within the station box. This was done to ensure that the passenger service area, including the island platform, stairs, escalators and the lift remained undisturbed, and the quality of passenger service was not compromised.
Certain service areas such as Ticket Operating Machines (TOM) and Automatic Fare Collection gates (AFC) were relocated at the mezzanine level and the location of the entry near the CSIR apartments as well as the vent shafts and firemen stairs at ground level were changed as per the new configuration.
The challenge was to design a tunnel ventilation system within the existing space. A tunnel ventilation system typically comprises a Tunnel Ventilation Fan (TVF) room, Air Plenums on either side of the TVF room and Air Nozzles connected to the air plenum on the tunnel side. The entire assembly occupies about 38-metre space on either end of the station box. In the new design, and the tunnel ventilation system has been accommodated at the concourse and mezzanine levels. At both ends, two TVFs were placed across the tracks, one over the other at the concourse and mezzanine levels and were connected with each other and the tracks by vertical plenums.
Apart from the tunnelling work and platform design, the allocation of functional necessities like Auxiliary Sub Station (ASS) and Environmental Control System rooms are very crucial at the initial stage of construction. These were accommodated at the concourse and mezzanine levels. Moreover, the location of ancillary buildings like Pump Room, Water Tanks, DG sets and Cooling Towers etc., had to be relocated over the station box near the CSIR apartments. Earlier, the ancillary building was supposed to be located in the private land, but could not be built as proposed earlier, since the land could not be acquired.
However, though these spontaneous makeshift arrangements seem minimal and even go unnoticed at the later stages of completion, the efforts in dealing with the issues at the initial stage has become a legacy for engineers to follow in the future.
* The article is a part of the book, Delhi Metro – Phase 3 Challenges, which encapsulates the various engineering challenges encountered by Delhi Metro during the construction of its Phase 3 corridors.