Metro-III will explore new depth — station at 29 mts,below another line

The average depth of existing Metro stations is 17 metres.

To prepare for the engineering feat,the Delhi Metro officials have begun a massive upgrade of construction infrastructure. The unique aspects include,the atopography and design of the station,the mode of construction and the machinery deployed.

Officials said the new Hauz Khas station will also be a vital Metro hub,connecting Metro lines between Gurgaon (Huda City Centre-Jahangirpuri) and Noida — thereby,reducing travel time.

The new station will be perpendicular to that of the Yellow Line at Hauz Khas. This,officials said,means use of new technology to accomplish the complex nature of construction.

Connecting NCR Gurgaon & Noida

Officials call the upcoming Hauz Khas station as the ‘Rajiv Chowk’ of the Phase-III.

The interchange will allow Yellow Line passengers from Gurgaon to switch to a direct Metro to Botanical Garden in Noida,instead of travelling all the way to Rajiv Chowk.

“This new interchange will contribute towards decongesting Rajiv Chowk station,which receives a daily average footfall of 5 lakh. The passengers travelling between Gurgaon and Noida,and South Delhi localities like Nehru Place and Kalkaji will not need to travel to Rajiv Chowk. They can change trains at Hauz Khas,” a DMRC spokesperson said.

The travel time between two NCR cities is expected to come down by at least half an hour,allowing commuters to reach from Noida to Gurgaon,and the other way around,in 50 minutes.

Metro officials expect the an average daily footfall of 1.69 lakh commuters,when the line opens in 2016.

The interchange on many levels

The subway from the south access point of the existing Hauz Khas Metro station will be widened to allow for integration with the Phase-III station.

“The subway,12 metres wide,would be constructed expanding from the present south entry/exit. Since the outline of the existing Hauz Khas station is a zig zag pattern,cut and cover technique will be used to integrate it with the new station,” an official said.

The subway will be constructed in five phases so as to not disrupt the traffic movement on Outer Ring Road. During the construction,the one entry/exit of the station would be closed temporarily. After the construction,there would be three entry/exit points.

After the commissioning of the interchange,the AFC gates at the existing station would be shifted to the concourse level from the ground level.

The interchange between the two stations will be at the concourse level. The new station will have four levels.

“The interchange between the two stations will be systematic and organised. The connectivity between new and old Hauz Khas stations will be connected through a ramp. Further,the subway will be expanded to make the movement convenient,” the official said.

Sixteen escalators and four elevators will be provided at the interchange point.

The construction 29 metres below

“The nature of the area is such that the construction of the Metro station will (have to) be carried out at such a depth. The Hauz Khas flyover meant that the station could come below it. For the new station,a location off the road was the most apt. At any other location,the station would have to be constructed at least 47 metres below. Since this was not viable,a depth of 29 metres was (viewed as) most appropriate,” a senior official said.

To allow construction of a station at such depths,the authorities drew up a unique design (see box).

A major challenge for the DMRC would be construction of a tunnel below an existing tunnel — the two tunnels will be separated by just three metres.

“To balance the pressure exerted due to torque of the moving rail coaches in the tunnel and (to ensure) zero settlement of soil does not take place,real-time online monitoring of the tunnels would be carried out constantly and at the diaphragm wall. Also crackmeters will be installed in the tunnel,” the official said.

The crackmeter,comprising a graduated steel scale and a transparent plastic cursor with a red hairline mark,monitors appearance of cracks on differential ground settlements.

Keeping the noise down

For the first time,the DMRC will be deploying sound barriers and floating tracks to reduce sound disruptions and curtail vibration.

“To ensure that the construction of the station does not affect the residential properties,Mass Spring System will be used. This will mitigate the vibrations generated by the passing trains at the source itself. While to curtail the noise during construction,sound absorbing material would be attached at the barriers,” the official said.

The floating track elastically separates the track slabs in the tunnels or on the viaducts from the supporting structure. The material used for isolation is a microcellular polyurethane elastomer. This will minimise the transmission of vibrations (structure-borne noise) to the surrounding establishments and also reduce the development of audible secondary airborne noise.

The system has been used on urban rail networks like Hong Kong,London,Vienna,Berlin,Singapore,Seoul and Sao Paulo.

The DMRC,at the construction phase,will fix sound barriers on the barricade boards,which will be four metres higher than usual. The inner side of the barricades would have a sound-absorbing material — more than one-third of the sound will be blocked by the arrangement.

“Since the station is coming up adjacent to residential colonies and a school,sound-proof barriers would be installed on the barricades,” the official said.

The station will be in the vicinity of Sarvapriya Vihar Colony,Delhi Colony,RBI Colony and Laxman Public School.

Hauz Khas will get deepest metro station

To provide anchorage to the deepest Metro station,the DMRC will lay a diaphragm wall 35 metres below ground.

The additional 6 metres depth (the station will be 29 metres deep) will provide support to the station.

For construction,a sophisticated machine — Cassa Grande with Baya grab machine — has been imported.

The equipment will ensure that the diaphragm wall is built vertically straight.

The top-down method of construction will be used. In this,the construction takes place as the excavation progresses.

The method accelerates construction and allows top surface (road) to be re-established quicker.