BUILDING ON WELLS
Once well rings are filled to the top with concrete, plinth beams are laid connecting all of them which help in transferring loads.
People who have visited Varanasi would have wondered about the lofty palace-like structures on the banks of river Ganga. How were they built many centuries ago and how are they still standing tall? What is the secret behind their sturdy construction? Look at port cities like Fort Cochin or the early buildings of Kolkata harbour. How could they stand on watery ground without our modern mass concrete foundations?
What our elders did then is today called as pile foundation, where thick and long trunks of hardwood trees are driven into the loose ground until they hit the hard strata deep underground. The mechanism driving them down will stop at that level indicating that the tree trunk has reached a safe level, capable of taking building load. Simultaneously, as these straight trunks are driven close by, they tighten the ground, increasing the effective density of the soil. In turn, the load bearing capacity of the ground increases by the combined effects of wooden piles driven up to hard strata and overall compaction achieved by close placing of these piles.
Concrete piles have replaced wooden piles today, but this is done mainly for large buildings with advanced mechanism, professional designs and skilled supervision. Thousands of smaller buildings and residential structures cannot afford to go for concrete pile foundation, due to exorbitant costs.
There is a simplified system called well ring foundation, applicable to any building on loose, water logged sites, where the conventional stepped stone foundation is not possible. Concrete footing would be expensive due to the excavation depths or in general we wish to reduce the consumption of steel and concrete towards more eco friendly architecture.
Pre-cast round rings are generally available in most parts of India, which are inserted into the ground while the open pit is dug manually. Though this method is for open water well, same could become a foundation by pouring concrete into the well. Most rings come in 3 to 4 feet diameter, ideally for the foundation width. The depth of the well ring foundation, diameter and spacing distance needs to be calculated by structural engineers. Further, either load bearing or frame construction can be adopted as decided by the engineers. In case unequal settlement is suspected, the well rings may have to be tied together not only by the plinth beam, but each ring foundation will need to be fixed into the plinth beam.
In very loose soil, while digging, the side walls may cave in or in high water table areas we may have to continuously pump water out while concreting. Very few engineers have designed well ring foundations; as such, ensuing proper technical calculations are mandatory, followed by quality workmanship at site.
Such ideas which resemble wooden pile may sound difficult; however once done, we realise they are doable again.