Presentation on theme: "Consolidation of Clays"— Presentation transcript:
1 Consolidation of Clays N. SivakuganDuration: 17 minutes
2 What 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).
3 What is Consolidation?This leads to settlements occurring over a long time,timesettlementwhich could be several years.
4 In granular soils…Granular soils are freely drained, and thus the settlement is instantaneous.timesettlement
5 During 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
6 During 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
7 One 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
22 Settlement 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
23 Settlement computations ~ computing e using e-log v’ plotIf the clay is normally consolidated,the entire loading path is along the VCL.initialvo’eoevo’+
24 Settlement 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’+
25 Settlement computations ~ computing e using e-log v’ plotIf an overconsolidated clay becomes normally consolidated by the end of consolidation,VCLvo’initialeoevo’+ p’
26 PreloadingPreloading at West Kowloon Expressway, Hong Kong. (5-10 m embankments for 2-5 months)
27 PreloadingPiezometers measure pore pressures and thus indicate when the consolidation is over.
28 Preloading Installation Cross section of PVDInstallationPrefabricated Vertical Drains to Accelerate Consolidation
29 Prefabricated Vertical Drains Installation of PVDs