HOW TO AVOID FOUNDATION FAILURE IN BLACK COTTON SOIL?

by

Black Cotton Soil

Black cotton soil has a tendency to shrink and swell excessively. When these type of soil come in contact with water, they swell and when becomes dry, it shrinks. This alternate process of swelling and shrinking results in the differential settlement of foundation which in turn causes cracks in building. The cracks thus formed are sometimes 15 to 20 cm wide and 2.5 to 4.5 m deep.

Therefore necessary precautions need to be taken during construction to avoid any damage to building foundation.

Following precaution should be employed during construction on black cotton soil.

Precautions to be Taken

  1. The maximum load on black cotton soil should be limited to 5 tonnes/m2. If there is a chance for water to come in contact with foundation, then the load should be limited to 4.9 tonnes/m2.
  2. Foundation should be placed at a depth where the cracks cease to extend. The minimum depth of foundation should be at least 1.5 m.
  3. The main wall of the building must be provided with all round reinforced concrete ties or bands.
  4. Reinforced concrete ties or bands having 10 to 15 cm deep should be placed at plinth level, lintel level and eaves level.
  5. In case the depth of black cotton soil is only 1 m to 1.5 m, then completely remove the entire black cotton soil and place the foundation below that depth.
  6. Try to avoid direct contact of black cotton soil with foundation material. This can be achieved by making wider trenches for foundation and filling spaces on either side of the foundation masonry with sand or morroum.
  7. Ram the bed of the foundation trench to make it farm and hard. On this rammed bed, spread a thick layer of morroum (i.e. 30 cm) in two layers, each layer being 15 cm. each layer should be water and rammed properly to get highest possible density. On this compacted layer of morroum, place either sand or stone upto desired height where concrete foundation bed has to be made.
  8. In case of important structures, raft foundation should be provided.
  9. For less important structures (such as boundary wall construction), the foundation should preferably taken at least 15 cm below the depth at which cracks in soil cease to occur.
  10. Construction should be done in dry season.
  11. For main walls or for load bearing walls, the width of the trench should be dug 40 cm wider than width of foundation. Then fill the space on either side of the trench (i.e. 20 cm in each side) with coarse sand. This is done to separate the foundation masonry from direct contact with black cotton soil. In case of compound wall this width of sand filling can be reduced to 15 cm on each side.
  12. Under reamed pile foundation is also a good choice of foundation in black cotton soil.

5 thoughts on “HOW TO AVOID FOUNDATION FAILURE IN BLACK COTTON SOIL?”

  1. Black cotton soil ehh, build in dry season is good idea I read, yes yes why did not Irene no think of that. How far down is water? Can you get 4 or six foot down with no water? One test hole to 8 or 10 foot or deeper to make sure you don’t have water within 2 foot of the bottom of 4 foot. If water is 8 foot or deeper for little small house maybe 2 bedroom with a plastic kite for a roof. Take black cotton soil out of ground in sections. Like hopscotch the game you jump in the 12 squares missing the square where you threw the rock.

    Take one section at a time. Maybe one week time or more to work one section. Rainy season good time to work sections unless you get water at 8 or six foot deep and it stays. If water is deeper in rain season spread out one block of black cotton soil on ground level. Find sand, screenings, furnace slag, 5 rock, drain stone. Find a material you can spread on top of your black cotton sand pizza crust that’s not more black cotton or leaves or branches or roots. 2 part filler to 1 part black cotton sand. Take u pizza out the oven and put it aside and make 11 more pizzas.

    If the bottom of your hole for black cotton sand makes wet wet quick sand, use 5mm to 8 or 9 cm sized rocks or stones. Mix sizes good like cake batter. Pack cake batter in bottom of black cotton holes until quick sand goes away. Push with tracker or cow or dozer, roller compactor on low vibrate one direction. Make rocks and stones hard like concrete floor or major highway to big city. Put gray cotton soil with rocks 1 to 1 or 2 cotton to 1 rock back In hole. Do same thing that you’re been doing make

    Reply

  2. Ours is a black soil area. I need to build a compound wall that is cost effective but withstand the troubles of black soil.i prefer not to go for concrete bases and pillars.i need some idea.will you share?

    Reply

  3. THNXX A LOT..it’s very helpful..
    but can u sand additivies name which is easily available.&send unique additivies (latest) also latest news for black cotton soil

    Reply

  4. i have to construct my house in my Agricultural land which is having black Cotton Soil . how much it is costlier the pile foundation structure than the normal structure constructed on plot where the strata is hard on 4 to 5 ft .
    Is it advisable to construct the Building in Agricultural land ( Black Cotton Soil ) or to purchase the plot of 2500 sq ft @ 15- 20 lacs .

    Reply

Leave a Comment