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Soil exploration, safe bearing capacity, improvement

Short answer

Soil exploration uses test pits, augering, wash boring, percussion, rotary drilling, SPT, and geophysical surveys. Safe bearing capacity is the maximum load per unit area safely supported without shear failure or excessive settlement, obtained by dividing ultimate capacity by factor of safety (2.5–3). Methods: compaction, drainage, gravel replacement, larger footing, stone columns, grouting, stabilisation, piles.

What do you know about the methods of soil exploration? Define safe bearing capacity of soil and describe briefly the methods of improving bearing capacity of soil.

Methods of soil exploration

  1. Test pits (trial pits): Pits dug 1.5 to 3 m deep; the soil is inspected and samples are taken. Cheap; for shallow depths and small buildings.
  2. Auger boring: A hand or power auger drills holes in soft soil up to about 10 m deep; gives disturbed samples.
  3. Wash boring: A water jet cuts the soil inside a casing; used in sand and clay.
  4. Percussion boring: A chisel breaks hard soil or rock.
  5. Rotary drilling: Core drilling for rock and hard strata.
  6. Sampling: Disturbed and undisturbed samples (thin-wall tube, split spoon).
  7. Field tests: Standard Penetration Test (SPT), static and dynamic cone penetration tests, vane shear test, plate load test.
  8. Geophysical methods: Seismic refraction and electrical resistivity, for large areas and depth profiles.
  9. Laboratory tests: Grain size, Atterberg limits, shear strength, consolidation.

The number and depth of boreholes depend on the size of the building and the variation of the soil; the depth of exploration is at least 1.5 times the width of the footing (the depth of significant stress).

Safe bearing capacity

Safe bearing capacity is the maximum intensity of load per unit area that the soil can carry safely without shear failure and with permissible settlement:

qs=quFSq_s = \frac{q_u}{FS}

where quq_u is the ultimate bearing capacity and FSFS is the factor of safety (2.5 to 3).

Methods of improving bearing capacity

  • Compaction by rolling and ramming.
  • Drainage of ground water.
  • Replacement by a compacted sand or gravel cushion.
  • Increasing the depth or width of the foundation.
  • Sand piles and stone columns.
  • Grouting and chemical injection.
  • Stabilisation with cement or lime.
  • Confinement by sheet piles; preloading; geosynthetics; or pile foundation.

✓ Answer checked by Claude Opus 5.5 (high effort)

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