Question: Explain types of foundations (with neat sketches) that can be provided for following conditions.

1) Black cotton soil up to depth of 10 cm.

2) Foundation of column close to boundary.

3) Multi-storeyed building on low bearing capacity of soil.

Civil Eng > Sem 8 > Design and Drawing of Reinforced Concrete structure

ddrcs mumbai university • 331 views
modified 7 weeks ago by gravatar for Ankit Pandey Ankit Pandey60 written 4 months ago by gravatar for tanya.tanyabarnwal tanya.tanyabarnwal0

(1) Black cotton upto depth of 10 m

1.Pad foundation

2.Pier foundation

3.Under-reamed pile foundation.

  • Such foundations are provided for construction purpose in black cotton or any expansive soil.

  • Under reamed pile is most suitable type foundation for black cotton soil. As it provides more stability to the structure and the ball present in the under reamed pile installed below the critical depth means below the moisture movement area which helps the structure to maintain its load bearing capacity.

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(2) Foundation of column close to boundary.

  • Shoe footing is the half footing cut-out from the original footing and it has a shape of shoe.
  • It is provided in the comer of the plot. Where there is no provision of setback area.
  • They are constructed on property boundary.
  • Column is provided or loaded at the edges of footing.
  • It is provided when the exterior column is close to the boundary or property line and hence there is no scope to project footing much beyond the column face.
  • Shoe footings are constructed when the soil bearing capacity is the normal 24 $\mathrm{KN} / \mathrm{m} 2$

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(3) Multi-storeyed building on low bearing capacity of soil.

  • Raft foundations are used for combining the footings of group of columns of building when column carry heavy loads on weak soils.

  • Also when the isolated footing occupy more than 75% of the plan area, raft foundations are used.

  • Centers of gravity of column loads and the footing are matched to obrain uniform upward soil pressure. If this is not possible, non-uniform pressures should be taken into account in design.

  • The exact manual analysis of raft foundation is not possible because the beams run in both the directions and share of the loads by these beams cannot be easily calculated.

  • In raft foundation the settlements under individual columns tend to be uniform.

  • Therefore inconventional design the reactions in the beam at their junction with the columns are so adjusted that their sum equals to column load.

  • Raft foundations may be used for buildings on compressible ground such as very soft clay, alluvial deposits and compressible fill material where strip, pad or pile foundation would not provide a stable foundation without excessive excavation.

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Advantages of raft foundation

  1. Raft or mat foundation is economic to combination of foundation and floor slab.
  2. It require little excavation.
  3. It can cope with mixed or porred ground condition
  4. It reduces differential settlement.
modified 7 weeks ago  • written 7 weeks ago by gravatar for Ankit Pandey Ankit Pandey60
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