Black cotton soils have a tendency to shrink and profusely bloom. This type of soil swells when exposed to water and shrinks when it dries. This alternating process of swelling and shrinkage results in differential settlement of the foundation which in turn causes cracks in the building. The cracks thus formed are sometimes 15 to 20 cm wide and 2.5 to 4.5 m deep.

Hence necessary precautions need to be taken during construction to avoid any damage to the foundation of the building.

The following precautions should be taken during construction on black cotton soil.

precautions to be taken

  1. Maximum load on black cotton soil should be limited 5 ton/m2, If there is a chance of water coming into contact with the foundation, the load should be limited 4.9 ton/m2,
  2. The foundation should be laid at such a depth where the cracks stop spreading. Minimum depth of foundation should be at least 1.5m,
  3. The main wall of the building should be provided with all-round reinforced concrete ties or bands.
  4. reinforced concrete ties or bands It should be placed at plinth level, lintel level and eaves level when it is 10 to 15 cm deep.
  5. If the depth of the black cotton soil is only 1 m to 1.5 m, remove the entire black cotton soil completely and place the foundation below that depth.
  6. try the Avoid direct contact of black cotton soil with foundation material, This can be achieved by creating a wide trench for the foundation and filling the spaces on either side of the foundation with sand or mortar.
  7. Ram dug the foundation trench to make the field more hard. Spread thick layer of Morum (i.e. 30 cm) in two layers on this covered bed, each layer of 15 cm. Each layer must contain water and penetrate properly to achieve the highest possible density. Place either sand or stone to the desired height on this compacted layer of moorum where the concrete foundation bed is to be made.
  8. In the case of critical structures, raft foundation should be provided.
  9. For less critical structures (such as boundary wall construction), the foundation should be driven at least 15 cm below the depth at which the soil stops cracking.
  10. should be done in construction dry season,
  11. For main walls or for load-bearing walls, the width of the trench should be dug 40 cm wider than the width of the foundation. Then fill the space on both sides of the trench (ie 20 cm on each side) with coarse sand. This is done to isolate the foundation masonry from direct contact with the black cotton soil. In case of compound wall this width of sand filling can be reduced to 15 cm on each side.
  12. Under remade pile foundation in black cotton soil is also a good alternative to foundation.

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.