If a building settles by 100 mm in a 5-year-period after construction, the type of soil below the foundation is _____ and the reason of settlement is _____. 

Explanation:

• Settlement over a long period of time—like 100 mm over 5 years—typically indicates consolidation, especially in clayey soils. 

• Clay has tiny pores, and water moves through it very slowly.

• It takes years for the water in clay to be expelled under a building’s load.

• Consolidation refers to gradual compression of a saturated clay layer due to the expulsion of pore water.

• Happens after construction, as the load from the structure compresses the soil.

• Unlike sand, where most settlement happens during or immediately after construction, clay settles over many years.

 Additional InformationCompaction:

• Compaction is the mechanical process of increasing the dry density of soil by rearranging soil particles to eliminate air voids.

• Achieved by applying external forces using rollers, rammers, or vibratory equipment.

• Commonly done during construction to improve bearing capacity and reduce future settlement.

• Compaction occurs immediately, often during site preparation or backfilling.

• No delayed settlement is expected after proper compaction.

• Granular soils like sand and gravel respond well to compaction.

• These soils have little to no cohesion, and densify easily when vibrated or tamped.

Consolidation:

• Consolidation is the time-dependent compression of saturated cohesive soils, primarily clays, due to expulsion of pore water under load.

• Happens when a building or structure applies pressure on the ground, squeezing out water from between clay particles over time.

• Controlled by drainage path length and permeability of the soil.

• Unlike compaction, consolidation occurs gradually, often over months to years, especially in deep clay layers.

• Most significant in clayey soils with low permeability and high compressibility.

• Not relevant for sandy soils, which drain quickly.