Download Guide to Cone Penetration Testing PDF

TitleGuide to Cone Penetration Testing
Tags Geotechnical Engineering Solid Mechanics Civil Engineering Nature
File Size4.2 MB
Total Pages138
Document Text Contents
Page 1

GUIDE TO
CONE PENETRATION

TESTING

www.greggdrilling.com

Page 2

Engineering Units



Multiples
Micro (μ) = 10-6
Milli (m) = 10-3
Kilo (k) = 10+3
Mega (M) = 10+6

Imperial Units SI Units
Length feet (ft) meter (m)
Area square feet (ft2) square meter (m2)
Force pounds (p) Newton (N)
Pressure/Stress pounds/foot2 (psf) Pascal (Pa) = (N/m2)

Multiple Units
Length inches (in) millimeter (mm)
Area square feet (ft2) square millimeter (mm2)
Force ton (t) kilonewton (kN)
Pressure/Stress pounds/inch2 (psi) kilonewton/meter2 kPa)
tons/foot2 (tsf) meganewton/meter2 (MPa)

Conversion Factors
Force: 1 ton = 9.8 kN
1 kg = 9.8 N
Pressure/Stress 1kg/cm2 = 100 kPa = 100 kN/m2 = 1 bar
1 tsf = 96 kPa (~100 kPa = 0.1 MPa)
1 t/m2 ~ 10 kPa
14.5 psi = 100 kPa
2.31 foot of water = 1 psi 1 meter of water = 10 kPa

Derived Values from CPT
Friction ratio: Rf = (fs/qt) x 100%
Corrected cone resistance: qt = qc + u2(1-a)
Net cone resistance: qn = qt – σvo
Excess pore pressure: Δu = u2 – u0
Pore pressure ratio: Bq = Δu / qn
Normalized excess pore pressure: U = (ut – u0) / (ui – u0)

where: ut is the pore pressure at time t in a dissipation test, and
ui is the initial pore pressure at the start of the dissipation test

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CPT Guide - 2010 Cone Penetration Test (CPT)

61




Hence, qall =
FS

Nc us


Where: FS is Factor of Safety, typically = 3.0.

Use a high FS to account for limitations in theory, underestimation of loads,
overestimation of soil strength, avoid local yield in soil and keep settlements
small.


Direct Approach to estimate Bearing Capacity (In-Situ Tests)

Based on in-situ tests, theory, model tests and past foundation performance.

SPT

 Empirical direct methods
 Limited to granular soils, however, sometimes applied to very stiff clays
 Often linked to allowable settlement of 25mm (Terzaghi & Peck)
 SPT of poor reliability, hence, empirical methods tend to be very

conservative

CPT

Empirical direct methods.

Granular soils:


qf = K qc (av)

where:
qc (av) = average CPT penetration resistance below depth of footing, z = B

Eslaamizaad & Robertson (1996) suggested K = 0.16 to 0.30 depending on
B/D and shape. In general, assume K = 0.16 (see Figure 34). Meyerhof
(1956) suggested K = 0.30. However, generally settlements will control.

Page 70

CPT Guide - 2010 Cone Penetration Test (CPT)

62







Figure 34 Correlation between bearing capacity of footing on cohesionless
soils and average cone resistance
(Eslaamizaad and Robertson, 1996)



Cohesive soils:


qf = Ksu qc (av) +  D


Ksu = 0.30 to 0.60 depending on footing B/D and shape and soil OCR and
sensitivity. In general, assume Ksu= 0.30 in clay

Page 137

10 Feet
6 Feet

COMMUNICATION
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Page 138

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