169_CEG 4012 Notes Fall 2011 CEG 4012 Notes Fall 2011

169_CEG 4012 Notes Fall 2011 CEG 4012 Notes Fall 2011 - 60...

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DF43 Drilled Shaft Toe Bearing: \.- 0 be careful about sludge on shaft bottom/ o also need to check soil/rock 18 to 28 under toe for voids and variability - use SPT or double tube rock core (~ 4" dia.) o Cohesive Soils (O'Neill Reese, 1999 FHWA manual) for 0/8 > 3, C u ~ 5.0 ksf (250 kPa) Iqt = N~ C U I where N: = 6.5 for C u = 0.5 ksf (25 kPa) = 8.0 for C u = 1.0 ksf (50 kPa) = 9.0 for C u ~ 2.0 ksf (100 kPa) C u = average C u for a depth of 28 below toe but if 8> 75" (1.9 m) then must reduce qt as follows where F r = 2.5 ~ 1.0 'P 1 B b + 2.5'11 2 4J 1 = 0.0085B b + 0.083(D/B b ) where Dand B b in ft 4J 1 = 0.0280B b + 0.083(D/B b ) where D and B b in m 4J 2 = O.014.JC: where C u in psf 40'2 = 0.065.JC: where C u in kPa o Cohesionless Soils (O'Neill Reese, 1999 FHWA manual) qt = 1.2N 60 < 60 ksf for qt in ksf qt = 57.5 N
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Unformatted text preview: 60 ~ 2900 kPa for qt in kPa where N 60 = the average SPT blow count (corrected to 60% energy) for a depth of 2 Bb below the toe (~ 50 blows per foot) if 8 &gt; 50&quot; (1.2 m) requires settlement of about 2.5&quot; (60 mm) at ultimate . 50&quot; h B&quot; h reduce qt If need less settlement: %r =-qt were b In inC es B b 1.2m h B' qtr =----s-qt were b In m b o Rock o special topic, consider rock type, jointing, core recoveries, qu RQD = rock quality designation =[r.(L&gt;4&quot;)]/length of run o conservatively use Terzaghi bearing capacity equation (typically lProck &gt; 45 deg, and ~ cohesion very high)...
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