Soil Consolidation and Settlement

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10 Questions

What is the primary cause of compression of soil layers?

All of the above

Which type of settlement is caused by the elastic deformation of dry soil?

Elastic settlement

What occurs during secondary consolidation settlement?

Plastic adjustment of soil fabrics

Which type of settlement is observed in saturated cohesive soils due to the expulsion of water from void spaces?

Primary consolidation settlement

What is the basis for elastic settlement calculations?

Theory of elasticity

What is the primary difference in behavior between sandy soils and clay soils when subjected to a stress increase?

Sandy soils exhibit rapid drainage of pore water, whereas clay soils exhibit slow drainage

What is the primary cause of settlement in soils?

Reduction in the volume of the soil mass

What is the relationship between the consolidation settlement and the elastic settlement in very compressible clays?

Consolidation settlement is greater than elastic settlement

What is the purpose of the pressure gauge attached to the cylinder in the simple model of saturated clayey soil?

To measure the excess hydrostatic pressure

What is the equation that represents the excess hydrostatic pressure in the simple model of saturated clayey soil?

P/A

Study Notes

Compressibility of Soil and Consolidation Settlement

  • Soil layers compress due to stress increase caused by construction of foundations or other loads, resulting in settlement.
  • Compression occurs due to:
    • Deformation of soil particles
    • Relocation of soil particles
    • Expulsion of water or air from void spaces

Types of Soil Settlement

  • Elastic settlement (or immediate settlement):
    • Caused by elastic deformation of dry soil and moist/saturated soils without change in moisture content
    • Calculations based on equations derived from elasticity theory
  • Primary consolidation settlement:
    • Result of volume change in saturated cohesive soils due to expulsion of water from void spaces
  • Secondary consolidation settlement:
    • Occurs in saturated cohesive soils due to plastic adjustment of soil fabrics
    • Additional compression at constant effective stress

Total Settlement of a Foundation

  • Total settlement (S T) = S c (primary consolidation settlement) + S s (secondary consolidation settlement) + S e (elastic settlement)

Fundamentals of Consolidation

  • When a saturated soil layer is subjected to a stress increase, pore water pressure increases suddenly.
  • In sandy soils, drainage occurs immediately, resulting in settlement.
  • In compressible clay layers, elastic settlement occurs immediately, but consolidation occurs over a longer period due to slower drainage.

Time-Dependent Deformation of Saturated Clayey Soil

  • Can be understood by considering a simple model consisting of a cylinder with a spring at its center.
  • Load applied to the piston causes excess hydrostatic pressure, which can be measured by a pressure gauge.
  • The excess hydrostatic pressure can be calculated using equation (11.1).

Test your understanding of soil compression and settlement caused by construction of foundations and other loads. Learn about the different types of settlement, including elastic settlement, and the factors that contribute to it.

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