28_CEG 4012 Notes Fall 2011 CEG 4012 Notes Fall 2011

28_CEG 4012 Notes Fall 2011 CEG 4012 Notes Fall 2011 - if...

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p11 6. Calculate void ratio e from R lO o for each load p and plot e-log p curve to find preconsoJidation pressure Pc using Casagrande constwction-: void ratio, e , \J, ~('tfJ (,lJ;(V ( "Apparent" Over·consolidatlon ""- log P a) Find 0; - a um curvalure (minimum radius) on reloaQ. .Rortioll.ot. .. laboratory cuNeo 5) Draw fiorizontalline and tangent to curve at point A c) Biseclangle between horizontal and tangent at point A. (1) Extrapolate straight line "virgi!Lcurv "to intersect bisector alprecons.olidation Rress.ure Pc o Preconsolidation, Pc ( =a' c) vs. C~[[ent elfectiveostress, a' 0 - - " . Soils "remember" past stresses, Pc (or a'c) represents the maximum past effective stress _ = a Nt o Over-consolidated (OC)
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Unformatted text preview: if p.' cr', o Normally consolidated (NC) H p. c-,. o Under-consolidated (UC) I' ,., L ,,-; o Over-consolidation Ratio Oc.R.-fl' /(J~; Reasons for pc > a'o : o overburden/load removal including erosion, dune movement, structure removal, melted~ I glaciers, etc. (this is the strict definition) I rise in groundwater levels which lowers effective stress o past desiccation induced capillary forces o seepage forces o tectonic forces, earth movements-Many researchers now believe that truly NC soils are rare, lowest natural OCR = 1.1 UC soils are infrequent and may indicate active consolidation (and lots of settlement!)...
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