The author of a number of technical papers on an ambitious project to rehabilitate a series of ageing brick sewers under Kolkata, recently travelled to Australia to present on the project.
Dr Ayanangshu Dey discussed the Kolkata Municipal Corporation project, which is considered to be one of the best examples of brick sewer rehabilitation, using sliplining and glass reinforced plastic liners.
Kolkata is the capital of West Bengal, India. The city was under British-colonial rule until the country’s independence in 1947. Today, it has a population of more than 4.5 million people and is considered one of the most congested urban environments in India, let alone the world.
Between 1757- 1911 Kolkata served as the administrative capital of pre-partition India for the British Raj. By the middle of the 19th century, its insalubrious sanitary conditions could only be compared to the legendary ‘great stink’ of London.
At the time, several sanitation schemes were proposed for the city; however, a municipal engineer at the time, William Clark’s design was adopted for implementation in 1858. This coincided with similar works being undertaken on London’s Central Sewerage System by Sir Joseph Bazalgette.
The Victorian-age infrastructure served Kolkata for more than a century, but by the end of the 20th century it was in desperate need of major refurbishment. The first phase of the £32 million (US$41 million) project, which started in 2007 and was completed in 2011, included the refurbishment of three major trunk sewers, with a combined length of 12 km, and represented a highly successful brick-sewer rehabilitation using slip-lining and glass reinforced plastic (GRP) pipes.
It featured a gruelling schedule that was essential due to the absence of stand-by sewers to divert the flow. The entire exercise was carried out between 11pm and 5am, during lean flow condition. Instead of blocking the sewers, operations were completed with over-pumping.
As the sewers were combined with lines carrying storm water with municipal sewage, monsoon seasons disrupted the progress every year for an estimated 3-4 months. The sewers were located in the centre of the city which also meant access pits had to be completely covered during the city’s festive seasons.
The project addressed issues such as the retention of discharge, capacities of sewers, regaining their structural integrity, reduction in water logging, protection against corrosion, future cleaning and maintenance, and the socio-environmental benefits. Trenchless Technology made the execution of the logistically complex rehabilitation possible in one of the most heavily congested urban areas in the world.
The execution of the project was the perfect example of municipal asset management and sustainable urban renewal for a colonial city that has been in existence for over 300 years. Its completion represented one of the most successful brick-sewer rehabilitation projects which has used sliplining to install GRP liners anywhere in the world.
Presenting the project
Dr Dey recently spoke about the rehabilitation project at three separate events in Australia; the first on 9 February 2017 in Sydney, and the other two on 15 and 16 February 2017 in Brisbane. Following his presentations, he answered several questions on the technical aspects of rehabilitation project; and the existence of other utility lines inside Kolkata sewers, which raised eyebrows among attendees.
Dr Ayan said almost all the existing electrical, communication cables, water lines inside sewers were eventually removed and that the new liner material would safeguard the sewers from any future intrusion.
His presentation also included meaningful information on the organisations which manage the various utility lines in the city, which at times during the project, caused coordination issues and delayed decisions which impacted on progress. The presentations were organised by the local officers of the American Society of Civil Engineers (ASCE), Institute of Civil Engineers (ICE) and Engineers Australia (EA). A number of ISTT members were in attendance in Brisbane.
This article was featured in the Summer edition of Trenchless International. To view the magazine on your PC, Mac, tablet, or mobile device, click here.
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