Unstable land poses sewer challenge in India
Shifting sands mean a change of direction for a new sewerage network in a coastal community.Bringing mains sewerage to people living on reclaimed spits of land off Mumbai (formerly known as Bombay) in India is no easy task.
Salt water, extremely deep bores, large diameter installations, working in landfill, all posed major problems for Michigan Engineering on a major project to improve sanitation for the thousands of people living there.
Many of the difficulties stemmed from the nature of the spits themselves which were once sandy islands just off the coast. Over the years the short stretch of water between the mainland and islands has been used as landfill so that now they are joined to the coast by thin fingers of land.
As the land extended, inhabitants moved in and the now densely populated spits were desperately in need of an efficient sewage system. The aim was to lay 500mm (197-inch) dia sewer pipes down each main street to drain waste from the open sewers running down the side streets.
Traditional digging methods soon proved unworkable. The reclaimed land was wet and extremely uneven, and as the pipes had to be laid 4-5 metres deep to connect with the existing sewers, this meant working well below the water table.
Michigan decided a different approach was necessary and, using a Vermeer® D80x100 NAVIGATOR HDD undertook horizontal directional drilling in tandem with the Vermeer Interragator GPS system. Specifically designed for non-specialists, the crew was able to work efficiently with the system in less than an hour. Vermeer also provided on-site training and support for all the start-up projects.
'These housing areas have grown up without any planning,' said managing director of Michigan Engineering, Mr Patel. 'That means nothing has been mapped, so the Interragator was invaluable in helping us locate underground obstacles.'
To make sure the PE pipe was in at the right angle, it was installed in 90m (295-foot) sections, boring from pit to pit and checking the gradient at each step. Due to the terrain, it was installed directly behind a 610mm (24-inch) fluted reamer.
'Going straight from the pilot bore to installing the 500mm pipe was an unusual and potentially risky manoeuvre,' said Mr Patel.
'However, working in such unstable conditions (below the water table and through landfill), there was a high probability that the bore would collapse if we enlarged it in stages.
'Although an unusual approach, we know the landfill wasn't properly compacted and so were reasonably confident there would be minimal resistance to the reamer and the pipe,' he added.
The successful installation of the sewer pipes as planned, using Vermeer HDD technology has attracted the attention of city officials across India.