Tackling loose soil

A look at a simple, traditional practice which is not adopted nowadays.

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When the British ruled India, among the many local practices they despised was that of the construction sector. To them, ideas of our past generations appeared unprofessional, hence introduced the European systems from their land. No doubt India benefitted in numerous ways by these new systems, but unfortunately, time-tested wisdom got lost in this process. Among these casualties, systems of foundation are notable.

Different regions of India followed different methods to solve the problem of transferring the building load to the ground. There were earth consolidations, wooden piles, boulders, stone slabs, deeper external wall foundations, sand packing and many more, which appeared flimsy to the British.

They introduced the method where dressed stone or masonry blocks are laid in layers, each upper layer narrower compared to the lower one, creating the stepped appearance, popularly believed to be stronger. It requires dressing the block into neat looking sizes, lime or cement mortar, back-filling the trench and needs to start from the hard strata of earth, hence could be many feet deep into the earth. In loose soil, such foundations demand much money and effort.

A simpler and traditional practice in this direction has been to drive down small poles 4 to 6 inch diameter into the soil at every one foot distance in both the directions. A normal 3 ft. wide and 3 ft. deep foundation trench is first dug out, with the top soil still loose.

Any locally available bamboo, casuarina, forest wood or such other poles which tend to grow narrow, straight and long are chosen with the desired length with the bottom tip left blunt or slightly tapered. The whole pole is given anti-termite treatment for durability and the top part wrapped with cloths or tied with ropes to avoid it splitting due to hammering.

Each one is steadily and slowly hammered down into the loose soil till it stops moving down. Technically, this method is nothing but a pile foundation, where modern concrete piles had their predecessor in wooden piles. This ensures the bottom strata of soil is made denser and tightly packed, hence is empowered to take greater load. Upon this layer of piles, masonry foundation was laid to the full width of trench, by packing stone boulders, quarried laterite, local bricks or any other local material.

The negatives

The flip side of this system is difficulty in gauging the increased load bearing capacity, which if needed can be found out by conducting on-site pile capacity testing. If the soil is excessively dry, intermittently water logged or termite infested, additional precautions need to be taken.

The driving down of the poles, mostly done manually, should be done honestly till they reach the layer of hard soil.

Soil types vary due to percentage contents of clay, sand, black cotton, gravel, laterite and such others, hence have varied expansion, water retention and shrinkage characteristics, which need to considered.

As modern science of construction is advancing, an occasional looking back may unearth forgotten knowledge systems that are resource saving and eco-friendly.

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Posted on January 11, 2014, in concepts and tagged , . Bookmark the permalink. Leave a comment.

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