Mega Tunnels of Samruddhi PKG-14

An Engineering Marvel by Afcons Infrastructure

The Package-14 of Samruddhi Mahamarg is going to be special for more than one reason. Besides having the country’s widest and Maharashtra’s longest road tunnels, it will give motorists a breathtaking view of the Sahyadri ranges while driving on Viaduct-II, which has been built over a dense forest area overlooking the mountains. While the mega tunnels were completed in early 2021, in a record time of two years, viaduct-II has come about on time to complete PKG-14 in its totality.
The PKG-14 is set to open soon, along with few other packages of the Maharashtra Samruddhi Mahamarg.

Geographical challenges

Package-14 is 13.1 km long and will connect Pimpri Sadroddin in Nashik with Vashala Budruk in Thane. The project’s location made the construction an arduous task. Package-14, executed by Afcons Infrastructure, is complete and has been handed over to the client.
“The project location falls in Igatpuri, which is the highest rainfall zone in Maharashtra. For some years, we faced unprecedented rainfall that took a toll on our tunnel construction and impeded our efforts at Viaduct-II. Due to the dense forest area, mountainous terrain, high rainfall, and lack of access roads, we had to proceed with extreme caution. Heavy showers and dense fog also caused visibility issues. However, we implemented the best safety practices to ensure a safe work environment,” said Sekhar Das, Project Manager at Afcons.”

Tunnelling in a downward gradient

The major focus of our execution was on the twin tunnels, which were completed in a record time of two years despite the pandemic. The tunnels at Igatpuri are divided into three sections: the shaded tunnel, the cast-in-situ cut-and-cover tunnel, and the main bored twin tunnel. Initially, the shaded tunnel was provided to reduce the water catchment area near the tunnel face. To achieve a safe overburden for the construction of the main tunnel, a cut-and-cover section, similar in size to the tunnel, was provided.
“Due to the geographical location, the tunnels were constructed using the New Austrian Tunnelling Method (NATM) and adopted the Heading & Benching excavation technique of NATM. In addition to the Heading & Benching excavation for speedy excavation, we also adopted a unique methodology in the construction of the tunnels. Initially, two vertical shafts were planned for the tunnels. After a detailed review of the terrain and execution methodology, one vertical shaft was changed to an inclined shaft. This change facilitated tunnel excavation by opening multiple work fronts. The inclined shaft was strategically placed at the center of the tunnel length, which helped us complete the excavation in record time,” explained Das.

The same inclined shaft can now be used as an escape tunnel in case of any emergency.
The tunnels are designed with a 2.49% downward gradient and an S-curve shape to mitigate the steep slope of the Ghat section. Since the roads were narrow and steep, heavy vehicle movement was impeded. The bulk construction material had to be stored on the Igatpuri side and moved in small quantities. Despite the pandemic, heavy monsoons, and other challenges, the mega tunnels were completed in a record time of two years. Each tunnel is 7.78 km long and 17.6 m wide, with three lanes in each direction.

Viaduct through Sahyadri ranges

Viaduct-II, which is 1.2 km long, was the second most challenging part of the project after the tunnels. It had to be constructed over a forest area with practi-cally no approach roads. The absence of access roads made the transportation of materials to the Viaduct-II location a major challenge. On top of that, navigating the monsoon season and setting up a camp in the area was an extraordinary task.

Besides its location, there was another unique challenge at Viaduct-II — its height. The viaduct is a balanced cantilever cast-in-situ bridge, 1.2 km in length. It has 35 piers, with the highest pier standing at 60 meters (equivalent to 20 floors). There are 29 spans, with the longest span measuring 98 meters.

The reinforcement steel cage was assembled on the ground, and the entire reinforcement module was lifted and placed for various components, including pier lifts, pier caps, hammerheads, and
segments. The Cantilever Form Traveller (CFT) shutter was also modified. This helped to reduce the cycle time for 5-meter balanced cantilever segment casting from 15 days to 9 days.

“Working at 60 meters in height, in a valley facing strong winds and heavy rainfall, was not easy. However, adequate safety measures were taken to complete the work. We are happy to have completed the project and finished the minor works within the stipulated time,” Das added.

Safety features in mega tunnels

The twin tunnels are equipped with a cross passage every 300 meters to facilitate evacuation in case of an emergency. There are a total of 26 cross-passages in both tunnels. Additionally, a layby area is provided every 750 meters to park any breakdown vehicles. The tunnels are equipped with the most advanced fire protection systems. It is noteworthy that a high-pressure water mist system, the first of its kind in any tunnel in India, has been installed.

Afcons Infrastructure Ltd
Web : www.afcons.com