Presentation on theme: "Consolidation of Clays"— Presentation transcript:
1Consolidation of Clays N. SivakuganDuration: 17 minutes
2What is Consolidation? When a saturated clay is loaded externally, GLthe water is squeezed out of the clay over a long time (due to low permeability of the clay).
3What is Consolidation?This leads to settlements occurring over a long time,timesettlementwhich could be several years.
4In granular soils…Granular soils are freely drained, and thus the settlement is instantaneous.timesettlement
5During consolidation… Due to a surcharge q applied at the GL,the stresses and pore pressures are increased at A.q kPa..and, they vary with time.GLsaturated clayu’A
6During consolidation… remains the same (=q) during consolidation.u decreases (due to drainage)while ’ increases,transferring the load from water to the soil.u’GLsaturated clayq kPaAu’q
7One Dimensional Consolidation ~ drainage and deformations are vertical(none laterally)~ a simplification for solving consolidation problemsq kPasaturated clayGLwater squeezed outreasonable simplification if the surcharge is of large lateral extent
22Settlement computations Two different ways to estimate the consolidation settlement:q kPa(a) using mvHsettlement = mv H=q(b) using e-log v’ plotnext slideeo, vo’, Cc, Cr, p’, mv-oedometer test
23Settlement computations ~ computing e using e-log v’ plotIf the clay is normally consolidated,the entire loading path is along the VCL.initialvo’eoevo’+
24Settlement computations ~ computing e using e-log v’ plotIf the clay is overconsolidated, and remains so by the end of consolidation,note the use of CrVCLvo’initialeoevo’+
25Settlement computations ~ computing e using e-log v’ plotIf an overconsolidated clay becomes normally consolidated by the end of consolidation,VCLvo’initialeoevo’+ p’
26PreloadingPreloading at West Kowloon Expressway, Hong Kong. (5-10 m embankments for 2-5 months)
27PreloadingPiezometers measure pore pressures and thus indicate when the consolidation is over.
28Preloading Installation Cross section of PVDInstallationPrefabricated Vertical Drains to Accelerate Consolidation
29Prefabricated Vertical Drains Installation of PVDs