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EM 1110.2.2504 31 Mar 94 Tell.. S.2 Ratio oI"~ (All. All... Dun..... ..... _ '111) Soi Trpe Sand Wood &.KO.76 &. K 0.55 &. K 0.76 &. K 0.50 Conc:re18 _I &. K 0.54 &. K 0.54 Sitt & Clay Tell.. W Velu. of & for Verloue In"""'" (eflw U.s. D8partm..1 of the IUvy '182) SoiTrJIlI (e) SlNI sheet pi... I ~ (deg) Cle8n gravel, gra",,' sand mixtures, ....-graded rocIdiIl with spaIIs 22 Cle8n sand, silty sand-gra",,1 mixture, ...gle-size herd rocIdill 17 Silly sand, graY81 ... ...d mixed wilh sitt or cIlly 14 Fine ...dy sIl, nonplastic sHt 11 (b) Concrete sheet piles Cle8n gra\l8l, gra",,1 sand mixtures, well-graded rockfiU wilh spaIIs 22.26 Cle8n sand, sillr sand-gra",,1 mixture, single-size herd roddiU 17.22 Silly sand, graY81 ... sand mixed with _tt or cIllr Fine sandy silt, nonplastic sil 17 14 TeIl..lI-4 eo.....tIon of Unclrelnecl Sheer Slr""llth of CIey (quc2c) SalUral8d ~ SPT Unn Weight Consisl8nc)' (psI) (bIowslft) (psI) V8fY Soft 0.500 0-2 cl00-110 Soft 500.1,000 3-4 100-120 Medium 1,000-2,000 5-8 110.125 Sliff 2,000-4,000 '.16 115.130 V8fY Still 4,000-8,000 16-32 120-140 Herd >8,000 >32 >130 3-4 (S) Since an undrained condition may be expecled to occur under "fasl" loading in the field, il represents a "short-Ienn" condition; in time. drainage will occur. and the drained strength will govern (the "Iong-Ienn" condi- tion). To model these conditions in the laboratory. three types of Iests are genera1ly used; unconsolidated undrained (Q or UU), consolidated undrained (R or CU), and consolidated drained (S or CD). Undrained shear strength in the laboratory is delermined from either Q or R Iests and drained shear strength is eslab- Iished from S IeSIS or from consoli~ undrained Iests with pore pressure measurements (R). e) ~ . (6) The undrained shear strength. Suo of a nonnally consolidaled clay is usually expressed by only a cohe- sion inlerCepl; and il is labeled Cu to indicate thaI , was Iaken as zero. Cu decreases dramatically with water cOnlenl; therefore. in design il is common to consider the fully salUrated condition even if a clay is partly saluraled in the field. Typical undrained shear strength values are presenled in Table 34. Su increases with depth (or effective stress) and this is commonly expressed with the ratio "S,jp" (p denoles the effective vertical stress). This ratio correlales roughly with plas- ticily index and oven:onsolidation ratio (Figures 3-2. 3-3. respectively). The undrained shear strength of many oven:onsolidated soils is further complicaled due to the presence of fISSures; this leads to a lower field strength than Iests on small laboratory samples indicale. e) (7) The drained shear strength of nonnally consoli- daled clays is similar to thai of loose sands (c' = 0). excepl thai , is generally lower. An empirical corre- lation of the effective angle of inlernal friction. ,'. with p1asticily index for nonnally consolidated clays is shown in Figure 34. The drained shear strenglh of over-con- solidaled clays is similar to thai of dense sands (again wilh lower f), where there is a peak strength (c' nonzero) and a "residual" shear strength (c' = 0). (8) The general approach in solving problems involving clay is that. unless the choice is obvious. both undrained and drained conditions are analyzed sepa- rately, The more critical condition governs the design. ToIaI stresses are used in an analysis wilh undrained shear strength (since pore pressures are "included" in the undrained shear strength) and effective Slresses in a drained case; thus such analyses are usually called tolal and effective SlreSS analyses. respectively. (9) Al low stress levels, such as near the top of a wall. the undrained strength is grealer than the drained e)