The recently inaugurated Zero Mile Freedom Park metro station is a multi-storied commercial building. The building has multi-level underground parking with a concourse level below the platform level. There is also planning for hotel rooms and luxury guest rooms at various floor levels above platform level.
As the track structure is coupled with the building structure at Zero Mile station, vibrations generated from the train wheels rolling on the tracks will be directly transmitted to the building structure.
The vibration of floors and walls may cause perceptible vibration, rattling of items such as windows etc or a rumble noise causing disturbance and annoyance to the occupants. In extreme cases,the vibration can also cause damage to building.
Therefore, it was necessary to assess the expected vibration level in the building during operation of regular metro train services. Accordingly Maha Metro engaged a renowned consultant in this field for assesment of vibration levels.
The analysis report submitted by the consultant revealed that the expected vibration level during train operation may be much higher than the prescribed threshold values. The consultant also prescribed various options for mitigation i.e reduction of vibration levels in the building. Out of the various available options,the consultant recommended that provision of the floating track slab on steel spring isolators as the best solution for mitigation of high vibration levels.
Accordingly, the track structure at Zero Mile station has been specially designed as a floating track slab (30 mm above station slab) supported on 176 chrome alloyed steel spring system isolators. This type of floating track slab on viaduct has been executed for the first time in Indian metro railway system.
The track slab of 135 m length, covering full length of the platform on both up and down lines has been concreted in single pour on each track slab without any expansion joint. The unique track slab mass spring system (MSS) is a maintenance free system and having a design life of 75 years.