To limit the load on the soil to 5.5 tonnes/sqr.m.
The minimum depth of foundation should be at least 1.5m.
To provide reinforced concrete ties or bands all around the main walls of the building. The R.C.C ties or bands which may be 10cm to 15cm deep should be placed at plinth level, lintel level and eaves level. In case of flat roof, R.C.C slab itself acts as a tie and as such no extra band needed to be provide near the roof in such cases.
If the depth of the black cotton soil at a given site is only 1 to 1.5m, the entire black cotton soil above the hard bed may be completely removed and the foundation may be laid on the hard bed below.
The swelling of soil in direct contact with the foundation material causes maximum damage. Hence it is necessary to prevent the direct contact of black cotton soil with masonry work below ground level. These can be achieved by making wider trenches for foundation and filling spaces on the either side of the foundation masonry with sand or moorum.
The bed of foundation trench should be made firm or hard by ramming it well. On the rammed bed a 30cm layer of good hard moorum should be spread in layers of 15cm, each layer being well watered and rammed before laying the next layer. On this layer either stone or sand bed should be provided to the desire height to place the foundation concrete bed block upon it.