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In Situ Testing. CPT & SPT. CPT Testing. CPT Testing. 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

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cpt testing3
CPT Testing

Three Measurements

qC = Cone-tip resistance

uP = Penetration pore pressure (piezocone)

fS = sleeve friction

Ratios

FR = friction ratio = fS / qC

Bq = pore pressure ratio = (uP-uh) / (qT –  'vo)

slide4

Sand

Clay

Crust

SCPTu Sounding, Memphis, Tennessee

Real-Time readings in computer screen

Penetration at 2cm/s

slide5
qT

Corrected cone-tip resistance

qT =qc + (1-an)uP

only for type 2 (type B) cones

an = 0.8 = fn(cone) net area ratio

cpt parameters
CPT-parameters

´ (Sands)

See page 129 fig. 4.16

´ = 17.6 + 11 log ( qC / (´vo.pa)0.5 ) Kulhawy & Mayne(1990)

´ = arctan[(0.1 +0.38 log (qC / ´vo))]

qC1= qC/(´vo.pa)0.5

cpt parameters7
CPT-parameters

Dr = relative density (sands)

Dr = 100 (qC1 / 305·OCR0.2 )0.5

if unknown, use OCR = 1

e = void ratio

e = 1.152 – 0.233·log(qC1) + 0.043 log(OCR)

cpt parameters8
CPT-parameters

OCR (iterative)

Ko = 0.192 ( qC / pa)0.22 (´vo / pa)-0.31 OCR 0.27 (1)

Ko = ( 1 - sin´)OCR sin ´(2)

(1) Mayne,CPT’95

(2) Mayne & Kulhawy,1982

a)Find ´

b)Vary OCR will both Ko values are similar

spt testing10
SPT Testing

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

spt testing11
SPT Testing

4) NSPT = N for last two 6 “ intervals

5) Retrieve sampler & save soil

6) Drill to next depth & go to step 2

NSPT = fn (Method of drilling, how clean boring is, hammer location, hammer type, “hangover level” of technician……..)

see p.117-118

spt testing12
SPT Testing

Efficiency corrections:

From “ NSPT” to “N60”

N60 = (E mCBCSCRNSPT) / .60

Em = hammer efficiency = fn (hammer type )  Table 4.3

P.119

CB = borehole dia. correction - table 4.4

Cs = sampler correction - table 4.4

CR = rod length correction - table 4.4

spt testing13
SPT Testing

More corrections:

NSPT  as   , so

pa = 100 kpa

(N1 )60  2N 60

N’s have been correlated with everything !!

(N1)60 = N60 ( pa/z)0.5

slide14

cu = undrained strength

gT = unit weight

IR = rigidity index

' = friction angle

OCR = overconsolidation

K0 = lateral stress state

eo = void ratio

Vs = shear wave

E' = Young's modulus

Cc = compression index

qb = pile end bearing

fs = pile skin friction

k = permeability

qa = bearing stress

DR = relative density

gT = unit weight

LI = liquefaction index

' = friction angle

c' = cohesion intercept

eo = void ratio

qa = bearing capacity

p' = preconsolidation

Vs = shear wave

E' = Young's modulus

 = dilatancy angle

qb = pile end bearing

fs = pile skin friction

SAND

CLAY

Is One Number Enough???

N