According to IS specifications, the minimum depth of foundation in sand and clay should be respectively

Explanation:

As per IS 1080:1985 – Code of Practice for Design and Construction of Shallow Foundations in Soils, the minimum depth of foundation depends on the type of soil to ensure stability against settlement, loss of bearing capacity, and seasonal moisture variation.

For Sand (800 mm minimum):

• Sand is a non-cohesive soil that is sensitive to disturbances and has low water retention.

• A minimum depth of 800 mm is recommended to ensure the foundation lies below the zone affected by surface weathering, erosion, and seasonal moisture fluctuation.

• This also helps mobilize sufficient bearing capacity from the deeper layers.

For Clay (900 mm minimum):

• Clay is a cohesive soil that is highly sensitive to shrinkage and swelling due to moisture content changes.

• A foundation placed at least 900 mm deep ensures it is below the active zone of seasonal moisture movement.

• This minimizes the risk of settlement or cracking due to volume changes in the clay.

 Additional Information

• The depth of foundation is the vertical distance between the ground surface and the base of the foundation.

• It must be adequate to:

  • Transfer loads safely to the ground.

  • Prevent damage from soil movement, frost, or erosion.

  • Avoid bearing failure and differential settlement.

These minimum depths are general guidelines, and actual design may require greater depths depending on load, local conditions, and soil investigation reports