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Foundation settlement causes and treatment

Short answer

A foundation is the lowest part of a structure transferring loads to the ground; types include shallow (spread, strip, raft) and deep (pile, pier, well). Settlement is caused by consolidation, weak or non-uniform soil, water table changes, overloading, adjacent works and earthquakes. Treatment includes underpinning, enlarging footings, grouting, drainage, load reduction, piles/micropiles and crack repair.

Define foundation with its types. What are the causes of foundation settlement and how can we provide treatment for foundation settlement?

Foundation

A foundation is the lowest part of a structure, in direct contact with the ground, which transfers the loads of the structure safely to the soil.

Types

  • Shallow foundations: spread (isolated) footing, strip (wall) footing, combined footing, strap footing, raft (mat) foundation, grillage.
  • Deep foundations: pile foundation, pier foundation, well (caisson) foundation.
 Shallow: [__|__]      Deep:  |   |   |   piles
 ----------------------     weak soil
                            ===hard layer===

Causes of foundation settlement

  1. Consolidation of compressible clay and silt layers under load.
  2. Weak, loose or filled soil and poor compaction.
  3. Non-uniform soil strata, giving differential settlement.
  4. Lowering of ground water table or seasonal shrinkage and swelling of clay.
  5. Overloading or unequal loading of foundation.
  6. Adjacent excavation and construction, and vibrations.
  7. Tree roots drawing moisture.
  8. Loss of soil by erosion or leakage, and underground voids.
  9. Earthquake causing densification and liquefaction.
  10. Faulty design or construction: footing too small or shallow.

Treatment of settlement

  1. Underpinning: Pit method, pile method, or by extending the footings deeper to a firm stratum.
  2. Enlarging the foundation to spread the load.
  3. Soil improvement: Grouting (cement, chemical), compaction grouting, jet grouting.
  4. Drainage: Control surface and ground water, repair leaking pipes.
  5. Reducing the load, or tying the structure with beams.
  6. Pile or micropile supporting under existing footing.
  7. Removal of trees, or root barriers.
  8. Repair of cracks after settlement is stabilised.

✓ Answer checked by Claude Opus 5.5 (high effort)

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