The mega tunnels of Samruddhi Mahamarg are an engineeringmarvel. However, this longest expressway in the country posed immensegeographical challenges, which were ably met by the experts at Afcons.

The Maharashtra Samruddhi Mahamarg, the longestexpressway in the country, is 701-km long and connects Mumbai with Nagpur. Withpart of the expressway now operational, the focus has shifted to the remainingpackages of the corridor.

After becoming fully operational, the traveltime will reduce by half between the two cities. The expressway will acceleratethe development of industrial corridors between Mumbai and Nagpur.

Afcons has delivered two packages – Package-2and Package-14 – in this entire corridor, which are complex and highlystructure-intensive. The Package-14 at Igatpuri will have the country’s widestand Maharashtra’s longest road tunnels, and it will also give motorists abreathtaking view of the Sahyadri ranges while driving on Viaduct-II, which hasbeen built over a dense forest area overlooking the mountains. It is, perhaps,the most critical package in the entire Samruddhi corridor because it comprisesIndia’s widest road tunnels in the Kasara Ghat area along with two viaducts,and an interchange.

Geographicalchallenges

The package is 13.1km long and will connectPimpri Sadroddin in Nashik with Vashala Budruk in Thane. The location of theproject made the construction an arduous task.

“The project location falls in Igatpuri, thehighest rainfall zone in Maharashtra. Some years, we faced unprecedentedrainfall that took a toll on our tunnel construction as well as impeding ourefforts at Viaduct-II. Because of a dense forest area, mountainous terrain,high rainfall, and lack of access roads, we had to tread with extremeprecaution. Due to heavy showers and dense fog, visibility remained an issue. However,we used the best safety practices to enable a safe work environment,” saidSekhar Das, Project Manager, Afcons.

Tunnellingin downward gradient

The major focus of the execution was on twintunnels, which were completed in a record time of two years despite thepandemic. The tunnels at Igatpuri are divided into three sections — shadedtunnel, cast in-situ cut and cover tunnel, and main bored twin tunnel.

At the start, the shaded tunnel is provided toreduce the water catchment area near the tunnel face. For achieving the safeoverburden for the construction of the main tunnel, cut and cover with similarsize of the tunnel is provided.

Due to the geographical locations, the tunnels wereconstructed with the New Austrian Tunnelling Method (NATM) by adopting the Headingand Benching excavation technique. In addition to the heading and benchingexcavation to facilitate speedy excavation of the tunnels, the project teamalso adopted a unique methodology in construction of the tunnels.

Initially, two vertical shafts were planned forthe tunnels. After a detailed review of the terrain and execution methodology,one vertical shaft was changed to an inclined shaft, which in turn facilitatedthe tunnel excavation by opening multiple work fronts.

The inclined shaft was strategically placed atthe centre of the tunnel length, which helped to complete the excavation inrecord time. The same inclined shaft can now be used as an escape tunnel incase of any emergency.

“The tunnels are designed with 2.49 per centdownward gradient and S-curve shape to mitigate the steep slope of the Ghatsection. As part of construction and pre-construction activities, we obtainedpermission from the authorities to form access roads in the forest area. Sincethe roads were narrow and steep, heavy vehicle movement was impeded. The bulkconstruction material had to be stored at the Igatpuri side and moved in smallquantities,” the Project Manager said.

The mega tunnels were completed in a record timeof two years despite the pandemic, heavy monsoon, and other challenges. Eachtunnel is 7.78km long and 17.6m wide, with three lanes in each direction.

Viaductthrough Sahyadri ranges

There are two viaducts in the project. Viaduct-II,which is 1.2km long, was the second most challenging part of the project afterthe tunnels. It had to be constructed over a forest area with practically noapproach roads.

In the absence of access roads, transportationof material to the Viaduct-II location was a major challenge. On top of that,negotiating the monsoon and setting up a camp in the area was an extraordinarytask.

Besides its location, there was another uniquechallenge at Viaduct-II — its height. The viaduct is a balanced cantilever castin-situ bridge with a length of 1.2km. There are 35 piers, with the highestpier standing at 60m (equivalent to 20 floors). There are 29 spans, and thelongest span measures 98m.

The reinforcement steel cage was assembled onthe ground, and the entire reinforcement module was lifted and placed forvarious components, including pier lifts, pier caps, hammer heads, segments,along with modification of the Cantilever Form Traveller (CFT) shutter. Theproject team was able to reduce the cycle time of 5.0m balanced cantileversegment casting from 15 to 09 days.

“Working at 60m height in a valley facing strongwind and heavy rainfall was not easy. However, adequate safety measures weretaken to complete the work. We are happy to complete the project and finish theminor works within the stipulated period,” Das added.

Tunnelfeatures

The twin tunnels are provided with a crosspassage every 300m to facilitate evacuation in case of any emergency. There area total of 26 cross-passages in both tunnels. Besides this, a lay by area isprovided every 750m to park any breakdown vehicles.

The tunnels are equipped with the most advancedfire protection system. It is noteworthy to mention that a high-pressure watermist system, which is a first for any tunnel in India, has been installed inthe tunnels.

Afcons has also delivered Package-2 ofMaharashtra Samruddhi Mahamarg in Wardha ahead of schedule. The 58.4km-long Package-2was the most structure intensive, with more than 200 structures in the project.It was inaugurated in December 2022 by honourable Prime Minister Shri NarendraModi as part of Phase-1 of the Samruddhi corridor.

PKG-14highlights

-         Total length: 13.1km.

-         Includes Maharashtra’s longest and India’s widest road tunnels.

-         Tunnel length: 8.0km.

-         Tunnel width: 17.6m.

-         Tunnelling completed in a record time of two years despite pandemic.

-         Multiple cross passages inside tunnels.

-         Tunnels equipped with modern ventilation, fire-fighting, and safetysystems.

-         First ever high-pressure water mist system in any tunnel in India for firesafety.

-         02 Viaducts.

-         01 Interchange.