The Chennai metro rail is the third largest metro rail system in India. It provides a high capacity mass transit sustainable solution to improve connectivity and reduce the growing traffic problems. The idea is to offer public transport that is properly integrated with other forms of public and private transport, including buses and suburban trains in heavily populated areas, in addition to improving the city’s liveability.
At a recent Indian Infrastructure conference, “Metro Rail Construction”, Anto Jos Menachery, general manager (UG-C), Chennai Metro Rail Limited (CMRL), spoke about the progress under the Chennai Metro Project, key challenges faced, lessons learnt and best practices. Excerpts…
Story so far
In the first phase, the Chennai metro rail operates over a length of 45 km and consists of two corridors – Corridor 1 from Washermenpet to Airport and Corridor 2 from Chennai Central to St Thomas Mount. Nearly 55 per cent of the corridors in Phase I are underground and the remaining are elevated. Of the 32 stations, 13 are elevated and the remaining 19 are underground. Further, intercorridor interchange stations are available under this network at Alandur (elevated) and Chennai Central (underground), respectively. Phase I of the Chennai metro is fully operational and was commissioned in stages. Stage 2A of the underground corridor commenced operations from May 14, 2017. Meanwhile, works on the Corridor 1 extension from Washermenpet to Wimco Nagar have been completed and the metro rail was opened for public on February 14, 2021. Corridor-1 extension has a total length of 9.05 km, of which 6.7 km is elevated and the remaining 2.4 km is underground. Of the eight stations on this section, six are elevated and two are underground.
Phase II of the Chennai Metro Rail has a total network length of 118.9 km, of which 42.6 km is elevated and 76.3 km is underground. It has three corridors under its ambit – Corridor 3 from Madhavaram to SIPCOT (45.801 km), Corridor 4 from Lighthouse to Poonamalle By pass (26.10 km) and Corridor 5 from Madhavaram to Sholinganallur (47 km). Two depots will also be developed under the project, one at Madhavaram and the other at Poonamallee. At present, work for Corridor 3, Phase II, of the project is under construction and has achieved physical progress of 3 per cent. The elevated section of Corridor 4 is also in progress and the current progress is 7 per cent. The ongoing work at Corridor 3 includes construction of a diaphragm wall for those underground stations where the tunnel boring machines (TBM) are proposed to be launched. The general consultant for the Corridor 3 and 5 project is a consortium of Nippon Koei India Private Limited, Aarvee Associates Architects Engineers and Consultants Private Limited and Balaji Railroad Systems Private Limited and the general consultant for Corridor 4 is a consortium of AECOM India, Oriental Consultants Global and Nippon Koei India Private Limited. Meanwhile, the contract for a few packages under Phase II of the project has been awarded to Larsen & Toubro, Tata Projects and a joint venture of the Hindustan Construction Company and KEC International.
Pain points and lessons learnt from Phase I
The execution and implementation of Phase I of the Chennai metro was challenging in terms of planning, design and construction. The alignment of the metro network was mostly along the arterial road corridors and meeting the minimum curve radius was, therefore, a challenge. Further, the planning had to be done keeping in mind future road expansion and maintaining vertical clearances. The design of the flyover proposal along the underground corridor also posed issues.
Another key challenge faced during project implementation was the geology and space constraint that the highly densified city of Chennai faces. The mixed soil condition (top layer being sandy and bottom layer being hard rock) impacts TBM selection and design. In addition to this, equipment such as disc cutters face extensive wear and tear, thereby requiring regular maintenance. Further, the geological conditions led to localised design changes, which resulted in delays. Other design challenges include crossing of railway tracks, rivers, bridges, etc., safeguarding heritage and old buildings along the alignment, intermodal connectivity, ensuring minimal public inconvenience and tackling the drainage aspects.
During the execution of the project, traffic management also emerged as a major issue given the limited road width. Other challenges incurred during the execution of the project include vibration and noise during excavation, cracks in buildings and their rectification, managing unforeseen issues, sink hole formation and its management. Meanwhile, foam and slurry leakages, plugging of borewells, road distortion, differential settlements and ground improvement, propping of old buildings with struts and extra precaution in case metro alignment passes in close proximity to heritage buildings are some other issues that were faced during project construction.
Best practices and the road ahead
Chennai metro offers a unique crossover experience at the Chennai Central metro station, wherein both corridors meet underground. Developed over a length of nearly 365 metres, the station spreads from the Ripon building to the Central Railway Station on the premises of heritage Buildings. It is a terminal station for Corridor 2 and has the provision for parking trains before service operation hours. It also has two levels of platforms as upper-track level (for Corridor 2) and lower-track level (for Corridor 1). It has been the retrieval point for six TBMs at breakthrough and is the only underground station that has three tracks at each platform level. It also has a network of subways built on the roof slab to enable crossing the Poonamallee High Road. It also has a subway parking provision.
Another unique feature of this stretch is the elevated Corridor 2 (provided to facilitate the crossing of the Kathipara flyover near Alandur) that is provided with three spans of a balanced cantilever, which were constructed without providing any temporary supports from underneath. Apart from this, traffic diversion schemes were implemented in stages, in order to tackle traffic management issues.
In a bid to move towards digitalisation, the the Project Management Information System is being deployed for Phase II. All documents and paperwork are now uploaded on the web portal and can be accessed online with ease. The documentation has been completely digitalised in Phase II. Drones are used for surveys while preparing the detailed project report.
For the construction of an elevated section of Phase I, trapezoidal segments have been used. These have been fabricated and brought to the site and post-tensioning has been adopted. During the construction of Phase II, a launching and retrieval area has been introduced within the underground stations, in order to avoid delays during construction and facilitate early completion of tunnel arrays. This is the key change in the underground construction technique from Phase I to Phase II. Under Phase I, the station box was used for launching and retrieval of TBMs.
Non-fare revenue for the project is expected to be generated from property development. Projects for the same are already underway under Phase I. Plans for building multi-storey buildings and shops are also under way.