Below ground: Diaphragm wall works for metro expansion in Indian metropolis

Chennai, India – A pulsating metropolis with millions of inhabitants, a port city and capital of the Indian state of Tamil Nadu – that's Chennai. As with many large cities in India, the city has experienced rapid population growth in recent years. The need for infrastructure is correspondingly high as a result. One solution to deal with the high traffic volume in the heavily built-up city is to move it underground. The Chennai Metro was opened in 2015 and so far has two lines with a total length of approx. 46 km. Now the network is to be expanded. Phase 2 of the extension includes the Chetpet Metro Station, a major project, what started in April of this year. As part of this project, BAUER Engineering India Pvt. Ltd., a subsidiary of BAUER Spezialtiefbau GmbH, was tasked with execution of the required diaphragm wall work.

In total, Bauer constructs more than 15,100 m² of diaphragm wall up to a depth of 35m. When constructing a panel, the work is divided into three steps: excavation of the trench using bentonite as the stabilizing slurry, installation of the steel reinforcement cages, and concreting work. "The steel reinforcement cages are each around 33 m long and weigh 35 t," explains Hassan Farhat, Project Manager at Bauer India. In total, 286 m³ of concrete is filled in for each diaphragm wall panel in just six hours, with 30 secondary panels produced by the beginning of November..

What's special about this project: There is zero tolerance for the trench excavation. However, this isn't the only challenge, as the site is in an area with significant rainfall in the monsoon season, i.e. during the construction phase. The ground composition of sand, silt, stiff clay and rock is also very demanding. "Another challenge is logistics. Since the new metro station is located directly in the urban area, the works need to be implemented in a very confined space. This requires extreme caution and excellent organization," continues Hassan Farhat.

A BAUER MC 96 duty-cycle crane with DHG-C hydraulic grab as well as an MC 128 duty-cycle crane with BC 40 cutter are being used for the works. In addition to this, digital tools such as the Bauer data management software b-project and the Virtual Site Installer are also being used.

"We are currently running on time and are more than satisfied," is Hassan Farhat’s summary of the project so far. "If everything continues to go as planned, we expect to successfully complete the project before the end of the year and thus a few weeks before the originally scheduled completion date at the end of January."