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Foundation classification and problems

Short answer

Foundations are classified as shallow (spread, strip, raft, etc.) when depth ≤ width, or deep (piles, piers, caissons) when deeper. Common problems are differential settlement, dampness, cracks, deterioration, soil movement, overloading, adjacent work effects, and earthquake damage.

What are the general classifications of foundation? What are the common problems of existing foundation?

Classification of foundations

Foundation is the lowest part of the structure which transfers the load to the ground. They are classified into two main groups.

1. Shallow foundations (depth Df≤D_f \le width BB, or less than about 3 m)

  • Spread (isolated) footing, wall (strip) footing, combined footing, strap (cantilever) footing, raft (mat) foundation, grillage footing, stepped footing.

2. Deep foundations (depth greater than width)

  • Pile foundation (bearing, friction, bored, driven), pier foundation, well (caisson) foundation, drilled shaft.
 Shallow: strip   [|____|]     Deep: pile   | | |
 ground ====================     weak soil  | | |
                                hard stratum  ===

Common problems of existing foundations

  1. Differential settlement causing cracks and tilting, as the soil is unequal or the load is increased.
  2. Dampness due to capillary rise through walls where DPC is poor.
  3. Cracks and deterioration of concrete, masonry and steel through sulphate attack, corrosion and weathering.
  4. Soil movement: Swelling and shrinking of clay, erosion, scour.
  5. Overloading by additional floors or change of use.
  6. Effect of adjacent excavation, vibration, and water table change.
  7. Earthquake damage and liquefaction.

Remedies: underpinning, grouting, soil stabilisation, drainage, widening of footing, and jacketing.

✓ Answer checked by Claude Opus 5.5 (high effort)

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