At least, two unique features describe the much awaited underground railway connection between Calcutta (Kolkata) and Howrah, two large cities situated on either side of River Hooghly. These are, the very concept of it was put forward by a Bengal-born British Engineer Sir Harley Hugh Dalrymple-Hay way back in 1921 and its twin tunnels under River Hooghly are the first of its kind in India.
Eventually, it took almost a century to realize the conception of Sir Dalrymple-Hay as the East West Metro Railway promises to inflict a significant and far reaching impact on Kolkata's transportation system in years to come and the way people commute between these two congested city centres. A field trip to these two under construction tunnels was organized by ICE Kolkata Chapter on 3rd June 2017 exclusively for local ICE members.
The East-West Metro Corridor Project is conceived to connect the East of Kolkata (Salt Lake Sector-V, Kolkata's IT Hub) with the West end i.e., Howrah (Kolkata's twin city). The whole project is being executed by Kolkata Metro Railway Corporation Limited (KMRCL) with partial financial support from JICA.
The entire stretch is divided into three parts, namely, UG-1 (underground portion from Howrah Maidan to New Mahakaran), UG-2 (underground portion from Esplanade to Subhash Sarobar) and elevated portion from Subhash Sarobar to Salt Lake Sector-V. This field trip was for the tunnel portion under UG-1 contract package. This UG-1 contract package is being executed by TransTonnelstroy-AFCONS Joint Venture (TTAJV).
A consortium (MYCEL) led by AECOM is the General Consultants (GC) to KMRCL. The works include 2-tier Howrah Maidan Station, one cross-over near Howrah Maidan Station, the 4-tier Howrah Station adjacent to present Howrah Railway Station (Kolkata's Railway Hub to rest of India) to provide interface between underground and surface railway transportation for commuter traffic coming to the cities from suburbs.
Under the project, there are twin tunnels each of 5.5 m internal diameter of total length of about 3 km and a Vent Shaft cum Emergency Exit on Kolkata's side by Hooghly river. The tunnels under river would be passing through mostly clayey silts at a depth of 11 to 15 m below river bed and under submergence of 13 m average tide water in the river. There are EPBM type two Tunnel Boring Machines (TBM) at work from Herrenknecht, Germany (named "Rachana" meaning "Composition" and "Prerana" meaning "Encouragement").
The tunnel is being constructed with pre-cast segments (5 regular segments and 1 key) of M50 grade concrete along with all necessary arrangement to ensure waterproofing, resistance to earthquake and floatation for a design life of 120 years. During tunnelling (other than utilities and land issues), the biggest challenge is to ensure the safety of buildings and structures above ground (some of them are almost century-old and remnants of the colonial era) with suitable preventive measures. Tunnels have successfully crossed Howrah DRM building with nominal damage and it is considered to be one of the achievements in this project, of course other than tunnelling below Hooghly river bed.
The site visit was approved by KMRC and facilitated by the engineers of both AECOM and AFCONS and was attended by about 30 ICE members, mostly civil engineering students who got a rare glimpse of such a huge and complex civil engineering project in a very congested urban area. On arrival, a briefing about the project works was given to all the attendees and this was followed by safety training by the site safety officer of AFCONS.
Every visitor was provided with safety shoe, helmet, jacket, water bottle, and was given a check of air quality and ambient conditions inside the tunnel. Then, the members were escorted by the engineering team of AECOM and AFCONS into the tunnel in two separate groups, one after the other.
The groups travelled through the eastern tunnel where the works have been stopped for the moment to negotiate with the authorities to safeguard the existing building for tunnelling operation underground on Kolkata side. The groups walked all the way up to the control room for the TBM and a little beyond that.
Markings inside the completed tunnel indicated the landmarks on the ground, e.g. Howrah Station, important buildings, River Hooghly, etc. It took almost an hour for the tunnel tour to be completed. On return to office, members were provided with tea and snacks. Various relevant questions were asked by the members following the visit which were responded by the engineers. Lastly, roll calls were taken and visitors' names were checked against the sign-up sheet before entering the tunnel.
The group dispersed on completion of the formalities and thanked the engineers for their support and guidance to make this a memorable field trip for them.