Consolidation settlement


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Consolidation settlement

  1. 1. Consolidation Settlement
  2. 2. What is Consolidation? When a saturated soil is loaded externally, GL saturated claythe water is squeezed out of the soil and the soil shrinks, over a long time may be upto several years depending upon the permeability of the soil this whole phenomenais called consolidation.
  3. 3. Concept of ConsolidationAs the time passes the water comes out of the soilvoids and so the volume of soil decreases, this is thecause of the settlement. The settlement is directly proportional to the decrease in volume of soil= The volume of squeezed out water
  4. 4. Settlement due to consolidation Settlement is the vertically downward movement of structure due to the shrinkage in volume of soil due to consolidation. e settlement H 1 eo
  5. 5. Settlement vs. TimeThis leads to settlements occurring over a long time, Settlement End of Primary Consolidation Cα Logarithm of Timewhich could be several years, depending upon the permiability of the soil.
  6. 6. Consolidation Settlement• It occurs due to the process of consolidation.• Clay and Organic soil are most prone to consolidation settlement.• Consolidation is the process of reduction in volume due to expulsion of water under an increased load.• It is a time related process occurring in saturated soil by draining water from void.• It is often confused with Compaction.• Consolidation theory is required to predict both rate and magnitude of settlement.
  7. 7. Since water flows out in any direction, the process isthree dimensional.But, soil is confined laterally. Hence, vertical onedimensional consolidation theory is acceptable.Spring analogy explains consolidation settlement.Permeability of soil influences consolidation.
  8. 8. Settlement-Void ratio Relation Equating the two expressions for average vertical strain,consolidation change in void ratiosettlement H e Ho 1 eoinitial thickness of initial void ratioclay layer
  9. 9. Settlement computations Two different ways to estimate the consolidation settlement: q kPa (a) using mv settlement = mv H =qH (b) using e-log v’ plot e settlement H 1 eo
  10. 10. Settlement by Mv Method ~co-eff of volume change=mv ~volumetric strain in a soil element per unit increase in stress no unitschange in volume original volume V i.e., mv V kPa-1 or MPa-1 kPa or MPa
  11. 11. Virgin Consolidation Line original state virgin consolidation line eo void ratio p’ log v’ vo’
  12. 12. Settlement computations~ computing e using e-log v’ plot If the soil is normally consolidated, the entire loading path is along the virgin compression line. initialeo e vo’+ vo’
  13. 13. Settlement computations If an overconsolidated clay becomes normally consolidated by the end of consolidation, initial eoe VCL vo’ p’ vo’+
  14. 14. Practical Applications Cross section of PVD InstallationPrefabricated Vertical Drains to Accelerate Consolidation
  15. 15. Consolidation Test settlement Increment of load At any degree of consolidation, comparison in time taken dial gauge for consolidation between laboratory & Topcap field with respect to drainage path iswater confining ring t = Time taken d = Drainage path sample porous stone