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Daily Digest Wed Oct 13 23:00:03 2004

 
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ibarua
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Joined: 26 Jan 2003
Posts: 1039

PostPosted: Sun Oct 17, 2004 2:22 am    Post subject: Daily Digest Wed Oct 13 23:00:03 2004 Reply with quote

17 October, 2004

Re.: Change of "Z" factors depending on soil conditions
--------------------------------------------------
Prof. A R Chandrasekaran has rightly pointed out the legal problems that may arise out of increased base shears due to change in "Z" factors. The BIS should protect those engineers who have designed a structure that may fail despite having been designed correctly according to the existing Codes. The BIS may also remember that retro-fitting is very costly and time consuming.

However, the really good thing about microzonisation is that the locations of pockets of liquefiable soils will be identified and thus, knowledge about liquefiable soils will be widely disseminated. I stress this point as many structural engineers, and indeed, so called geo-technical experts seem to be blissfully unaware of the dangers posed by liquefiable soils. As an example, I may quote the instance of a Central University being built on the north bank of the river Brahmaputra in Assam in seismic zone V. The site is ringed by a number of known epicentres of earthquakes of maginitude 5.5 to 8 on the Richter scale at a distance of 25 to 50 km. When I happened to be at the project site as a casual visitor, a mere visual inspection of the excavation in the foundation of a building was enough to tell me that the soil at the site could be prone to liquefaction. The soil was cohesionless and fine grained, and appeared to be unconsolidated. A perusal of the soil investigation reports of the site elicited not even a whisper about liquefaction. I conveyed my apprehensions to the project authorities, who, at my suggestion, commissioned a detailed investigation to determine the possibility of liquefaction or rule it out. This investigation confirmed my worst fears: the foundation soil was indeed prone to liquefaction, which could be triggered at contact pressures as low as 3 t per sq.m. While the soil could be reconditioned for future construction, buildings already constructed are sitting on dangerous ground. I also saw fr
the Government of India under construction in a nearby area. As far as I know, the project authorities there are unaware of the dangers lurking beneath their buildings.  

It is perhaps not entirely coincidental that in both these projects, the consultants were chosen on the basis of the "lowest tender".  Who will educate the owners and builders of such multi-crore projects?

Indrajit Barua.
Guwahati, Assam.
(ibarua@deguild.com)

On Wed, 13 Oct 2004 general@sefindia.org wrote :
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