Consolidation settlement

Consolidation settlement

• 1.
  Consolidation Settlement
• 2.
  What is Consolidation? When a saturated soil is loaded externally, GL saturated clay the water is squeezed out of the soil and the soil shrinks, over a long time may be up to several years depending upon the permeability of the soil this whole phenomena is called consolidation.
• 3.
  Concept of Consolidation Asthe time passes the water comes out of the soil voids and so the volume of soil decreases, this is the cause of the settlement. The settlement is directly proportional to the decrease in volume of soil= The volume of squeezed out water
• 4.
  Settlement due toconsolidation 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.
  Settlement vs. Time Thisleads to settlements occurring over a long time, Settlement End of Primary Consolidation Cα Logarithm of Time which could be several years, depending upon the permiability of the soil.
• 6.
  Consolidation Settlement • Itoccurs 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.
  Since water flowsout in any direction, the process is three dimensional. But, soil is confined laterally. Hence, vertical one dimensional consolidation theory is acceptable. Spring analogy explains consolidation settlement. Permeability of soil influences consolidation.
• 8.
  Settlement-Void ratio Relation Equating the two expressions for average vertical strain, consolidation change in void ratio settlement H e Ho 1 eo initial thickness of initial void ratio clay layer
• 9.
  Settlement computations Two different ways to estimate the consolidation settlement: q kPa (a) using mv settlement = mv H =q H (b) using e-log v’ plot e settlement H 1 eo
• 10.
  Settlement by MvMethod ~co-eff of volume change=mv ~volumetric strain in a soil element per unit increase in stress no units change in volume original volume V i.e., mv V kPa-1 or MPa-1 kPa or MPa
• 11.
  Virgin Consolidation Line original state virgin consolidation line eo void ratio p’ log v’ vo’
• 12.
  Settlement computations ~ computinge using e-log v’ plot If the soil is normally consolidated, the entire loading path is along the virgin compression line. initial eo e vo’+ vo’
• 13.
  Settlement computations If an overconsolidated clay becomes normally consolidated by the end of consolidation, initial eo e VCL vo’ p’ vo’+
• 14.
  Practical Applications Cross section of PVD Installation Prefabricated Vertical Drains to Accelerate Consolidation
• 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 is water confining ring t = Time taken d = Drainage path sample porous stone