Kolkata Metro East - West Project

Twenty four self bored tests were carried out at four critical locations along the alignment of the proposed metro in Kolkata, India. The pressuremeter testing component of the site investigation had been specified by W S Atkins. For the most part the tests were conventional in material that behaved either as a clay or sand. What was different about this project was the technical and practical difficulties that had to be overcome to achieve success - see figure 1.

Fig.1 Self boring in Kolkata (click for full-size)

The work was conducted on a 24 hour basis at pavement locations in the heart of the city. The only rig available turned out to be a small, light and rather old quill drive system where most of the controls had long broken down. Rate of rotation and advance was down to the skill of the driller, who knew his rig and how to coax results from it. On more than one occasion the rig rotation system broke down whilst driving the pressuremeter, and the boring was completed by rotating rods by hand.

In some ways a worse problem was an inadequate water pump, as no boring is possible if the pump is not delivering a sufficient flow. However as our report noted at the time, these issues were a problem for the rate of progress of the fieldwork rather than the tests themselves, which were of reasonable quality.

Some of the expansions in the more clay-like material were turned into consolidation tests. The tests typically took two hours to complete, and were popular with the drilling crew. There is an increasing need for complex transport infrastructure in such locations and this project is typical of the kind of testing we are asked to do.