33_CEG 4012 Notes Fall 2011 CEG 4012 Notes Fall 2011

33_CEG 4012 Notes Fall 2011 CEG 4012 Notes Fall 2011 - and...

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p16 o Graphical presentation of Fluid-Filled Cylinder with Spring Analogy: , , , Depends on Soil Properties Soil lIu (excess) ....................................................... _ ...... ...... ----- !i.crv , ... ~cr'v ,- , , , , , Pressure Depends on Opening Size .............................................. ~ ...;.z._. ... ~ ---- p ,- ........ PSPRING , " ----- I Analogy PWATER Force Time Time o When a load is applied to a saturated clay soil, it is initially carried by the pore water as an excess pore water pressure (over hydrostatic), lIu. The applied load, due to a foundation, increases the pore pressure already there. o With time, water will move out of the clay layer to the surface, or to some drainage boundary. The rate of this movement is primarily a function of the soil permeability and the layer thickness. o As the water moves out, the excess pore water pressure decreases, and the soil skeleton (spring) carries some of the stress. Also, a volume decrease occurs, and thus settlement. o Settlement will cease at Pc when the excess pore water pressure has dissipated to zero,
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Unformatted text preview: and there is no more tendency for water to flow out of the clay. o The process may take 100 yrs to occur (Palacio de Bellas Artes, Mexico) o For sands, the process is instantaneous, Le. no "consolidation settlement". o Normally use simple theories for saturated clays and 1-D flow (vertical or radial). o Example: Clay y=120pcf I Pi T I 10 It 10 It Mat foundation 32 It x 32 It q = 679 psf, point P at z = 10 It m: B/z:I!/'" 1.& n :Uz: 1&1"0'_'., I : 0,221 tJ.crv: 'I (I, 1'I) (U. 111 J' bOO nt @ Point P befgre buildin.a: "-" ~ 10 lll.u)~ I1.OUrs~ \.l~ 1l)(~1. .cl).-(,). .'1 fSr cr~: (J",,-"'-~ 5 l bpd II Stress, psf lI"v = 600 pst----""' . .....--;cr'v , , , , , , lIu @ 1=0, immediately alter building: tlv ~ t1ll0~ /,c1O<: '&ttl t"H LlIA: 110",,: boo fj~ \ .... ", \"t-olAlA' b7tr-+ [,00::: I U'l cr' v : ~-v..: 1'i"o-IU1: 5)6 AU'v :: 0 @ I = long lime cr,,: 1'100~' bOo:: ,goo fj( Liv. .: o,c,~('2'II'Jr Time, yrs (j'v: cr"-.... : l~oo-(,2'( ':" Ilit fJf .d tr til (, DO fSr...
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