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Published byDinah Norton Modified about 1 year ago

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In Situ Testing CPT & SPT

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CPT Testing

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Three Measurements q C = Cone-tip resistance u P = Penetration pore pressure (piezocone) f S = sleeve friction Ratios FR = friction ratio = f S / q C B q = pore pressure ratio = (u P -u h ) / (q T – ' vo )

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SCPTu Sounding, Memphis, Tennessee Real-Time readings in computer screen Penetration at 2 cm/s Sand Clay Crust

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qTqT Corrected cone-tip resistance q T = q c + (1-a n )u P only for type 2 (type B) cones a n = 0.8 = fn(cone) net area ratio

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CPT-parameters ´ (Sands) See page 129 fig. 4.16 ´ = 17.6 + 11 log ( q C / ( ´ vo.p a ) 0.5 )Kulhawy & Mayne(1990) ´ = arctan[(0.1 +0.38 log (q C / ´ vo ))] q C1 = q C /( ´ vo.p a ) 0.5

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CPT-parameters D r = relative density (sands) D r = 100 (q C1 / 305·OCR 0.2 ) 0.5 if unknown, use OCR = 1 e = void ratio e = 1.152 – 0.233·log(q C1 ) + 0.043 log(OCR)

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CPT-parameters OCR (iterative) K o = 0.192 ( q C / p a ) 0.22 ( ´ vo / p a ) -0.31 OCR 0.27 (1) K o = ( 1 - sin ´ )OCR sin ´ (2) (1) Mayne,CPT’95 (2) Mayne & Kulhawy,1982 a)Find ´ b)Vary OCR will both K o values are similar

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SPT Testing

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Procedure 1) Drill boring (hole) 2) Insert SPT sampler (hollow) 3) Drive sampler into the ground 18” & count N of blows to drive each 6” interval if N for 6” > 50 if N for all 18” >100 Refusal

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SPT Testing 4) N SPT = N for last two 6 “ intervals 5) Retrieve sampler & save soil 6) Drill to next depth & go to step 2 N SPT = fn (Method of drilling, how clean boring is, hammer location, hammer type, “hangover level” of technician……..) see p.117-118

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SPT Testing Efficiency corrections: From “ N SPT ” to “N 60 ” N60 = (E m C B C S C R N SPT ) /.60 E m = hammer efficiency = fn (hammer type ) Table 4.3 P.119 C B = borehole dia. correction - table 4.4 C s = sampler correction - table 4.4 C R = rod length correction - table 4.4

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SPT Testing More corrections: N SPT as , so p a = 100 kp a (N 1 ) 60 2N 60 N’s have been correlated with everything !! (N 1 ) 60 = N 60 ( p a / z ) 0.5

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N D R = relative density T = unit weight LI = liquefaction index ' = friction angle c' = cohesion intercept e o = void ratio q a = bearing capacity p ' = preconsolidation V s = shear wave E' = Young's modulus = dilatancy angle q b = pile end bearing f s = pile skin friction SAND c u = undrained strength T = unit weight I R = rigidity index ' = friction angle OCR = overconsolidation K 0 = lateral stress state e o = void ratio V s = shear wave E' = Young's modulus C c = compression index q b = pile end bearing f s = pile skin friction k = permeability q a = bearing stress CLAY Is One Number Enough???

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