3 Terms, definitions and symbols

3.1 Terms and definitions

For the purposes of this document, the following terms and definitions apply.

3.1.1

average surface roughness

Ra

average deviation between the real surface of the cone penetrometer and a medium reference plane placed along the surface of the cone penetrometer

3.1.2

cone

conical shaped bottom part of the cone penetrometer and the cylindrical extension

NOTE 1 When pushing the penetrometer into the ground, the cone resistance is transferred through the cone to the load sensor.

NOTE 2 This part of ISO 22476 assumes that the cone is rigid, so when loaded its deformation is very small relative to the deformation of other parts of the cone penetrometer.

3.1.3

cone penetration test

CPT

pushing of a cone penetrometer at the end of a series of cylindrical push rods into the ground at a constant rate of penetration

3.1.4

cone penetrometer

assembly containing the cone, friction sleeve, any other sensors and measuring systems as well as the connection to the push rods

NOTE An example of a cone penetrometer is shown in Figure 1; for other filter locations, see Figure 2.

Cone resistance and sleeve friction load cells in compression Cone resistance load cell in compression and sleeve friction load cells intension Subtraction type cone penetrometer
a) Cone resistance and sleeve friction load cells in compression b) Cone resistance load cell in compression and sleeve friction load cells intension c) Subtraction type cone penetrometer

Key

  • 1 sleeve load cell
  • 2 point load cell overload protection device
  • 3 cone load cell
  • 4 thread
  • 5 soil seal
Figure 1 — Cross section of an example of a cone penetrometer

3.1.5

cone resistance

cone penetration resistance

3.1.6

corrected cone resistance

qt

measured cone resistance, qc, corrected for pore pressure effects

3.1.7

corrected friction ratio

Rft

ratio of the measured or corrected sleeve friction to the corrected cone resistance measured at the same depth

NOTE Usually the measured sleeve friction is used; however, if available, the corrected sleeve friction is used.

3.1.8

corrected sleeve friction

ft

measured sleeve friction, fs, corrected for pore pressure effects

3.1.9

dissipation test

measurement of the pore pressure change with time during a pause in pushing while holding the cone penetrometer stationary

3.1.10

electrical cone penetration test

cone penetration test where forces are measured electrically in the cone penetrometer

3.1.11

excess pore pressure

Δu1, Δu2, Δu3

pore pressure in excess of the ambient pore pressure at the level of the filter caused by the penetration of the

cone penetrometer into the ground:

Δu1 = u1 – u0
(1)
Δu2 = u2 – u0
(2)
Δu3 = u3 – u0
(3)

3.1.12

filter element

porous element in the cone penetrometer that transmits the pore pressure to the pore pressure sensor, maintaining the geometry of the cone penetrometer

3.1.13

friction ratio

Rf

ratio of the measured sleeve friction to the measured cone resistance at the same depth

3.1.14

friction reducer

local and symmetrical enlargement of the diameter of a push rod to obtain a reduction of the friction along the push rods

3.1.15

friction sleeve

section of the cone penetrometer where friction between the soil and the sleeve is measured

3.1.16

in situ equilibrium pore pressure

u0

original in situ pore pressure at filter depth

3.1.17

inclination

angular deviation of the cone penetrometer from the vertical

3.1.18

initial pore pressure

ui

measured pore pressure at the start of the dissipation test

3.1.19

measured cone resistance

qc

division of the measured force on the cone, Qc,by the projected area of the cone Ac:

qc = Qc/Ac
(4)

3.1.20

measured pore pressure

u1, u2, u3

pressure measured in filter element during penetration and dissipation testing

NOTE The pore pressure can be measured at several locations as follows {see Figure 2):

u1 on the face of the cone;

u2 on the cylindrical section of the cone {preferably in the gap between the cone and the sleeve;

u3 just behind the friction sleeve.

Locations of pore pressure filters

Key

  • 1 friction sleeve
  • 2 cone penetrometer
  • 3 cone
Figure 2 — Locations of pore pressure filters

3.1.21

measured sleeve friction

fs

division of the measured force acting on the friction sleeve, Fs, by the area of the sleeve, As:

fs = Fs/As
(5)

3.1.22

measuring system

all sensors and auxiliary parts used to transfer and/or store the electrical signals generated during the cone penetration test

NOTE The measuring system normally includes components for measuring force (cone resistance, sleeve friction), pressure (pore pressure), inclination, clock time and penetration length.

3.1.23

net area ratio

a

ratio of the cross-sectional area of the load cell or shaft, Ast, of the cone penetrometer above the cone at the location of the gap where fluid pressure can act, to the nominal cross-sectional area of the base of the cone, Ac

NOTE See Figure 6.

3.1.24

net cone resistance

qn

measured cone resistance corrected for the total overburden soil pressure

3.1.25

net friction ratio

Rfn

ratio of the sleeve friction to the net cone resistance measured at the same depth

3.1.26

normalized excess pore pressure

U

excess pore pressure during a dissipation test compared to the initial excess pore pressure

NOTE See 7.4.

3.1.27

penetration depth

z

vertical depth of the base of the cone, relative to a fixed point NOTE See Figure 3.

3.1.28

penetration length

l

sum of the lengths of the push rods and the cone penetrometer, reduced by the height of the conical part, relative to a fixed horizontal plane

NOTE 1 See Figure 3.

NOTE 2 The fixed horizontal plane usually corresponds to the level of the ground surface (on shore or off shore). This can be different from the starting point of the test

Penetration length and penetration depth

Key

  • a fixed horizontal plane
  • b base of conical part of cone
  • l penetration length
  • z penetration depth
Figure 3 — Penetration length and penetration depth (schematic only)

3.1.29

piezocone penetration test

CPTU

electrical cone penetration test with measurement of the pore pressures around the cone

3.1.30

pore pressure ratio

Bq

ratio of the excess pore pressure at the u2 filter position to the net cone resistance

3.1.31

push rod

part of a string of rods for the transfer of forces to the cone penetrometer

3.1.32

reference reading

reading of a sensor just before the penetrometer penetrates the ground or just after the penetrometer leaves the ground

NOTE 1 In offshore situations, it is the reading taken at the sea bed or at the bottom of a bore hole with water pressure acting.

NOTE 2 With tests starting on shore from the ground surface, the reference reading equals the zero reading.

3.1.33

thrust machine

equipment that pushes the cone penetrometer and rods into the ground at a constant rate of penetration

3.1.34

total overburden stress

σv0

stress due to the total weight of the soil layers at the depth of the base of the cone

3.1.35

zero drift

absolute difference between the zero readings (or reference readings) of a measuring system at the start and after completion of the cone penetration test

3.1.36

zero reading

stable output of a measuring system when there is zero load on the sensors, i.e. the parameter to be measured has a value of zero, while any auxiliary power supply required to operate the measuring system is switched on

3.2 Symbols

Symbol Name Unit
Ac cross-sectional projected area of the cone mm2
An cross-sectional area of load cell or shaft mm2
As surface area of friction sleeve mm2
Asb cross-sectional area of the bottom of the friction sleeve mm2
Ast cross-sectional area of the top of the friction sleeve mm2
a net area ratio  
Bq pore pressure ratio  
Cinc correction factor for the effect of the inclination of the cone penetrometer relative to the vertical axis  
dcone diameter of the cone at a specified height mm
dc diameter of the cylindrical part of the cone mm
dfil diameter of the filter mm
d2 diameter of the friction sleeve mm
Δu1, 2, 3 excess pore pressure at filter locations 1, 2 and 3 MPa
Fs axially measured force on the friction sleeve kN
fs measured sleeve friction MPa
ft corrected sleeve friction MPa
hc height of the conical section of the cone mm
he length of the cylindrical extension of the cone mm
l penetration length m
ls length of the friction sleeve m
Qс axially measured force on the cone kN
qс measured cone resistance MPa
qn net cone resistance MPa
qt corrected cone resistance MPa
Ra average surface roughness urn
Rf friction ratio %
Rft corrected friction ratio %
Rfn net friction ratio %
t time s
t50 time needed for 50 % excess pore pressure dissipation s
U normalized excess pore pressure  
u pore pressure MPa
ui pore pressure at the start of the dissipation test MPa
ut pore pressure at time t during a dissipation test MPa
u0 in situ, initial pore pressure MPa
u1 pore pressure measured at location 1 MPa
u2 pore pressure measured at location 2 MPa
u3 pore pressure measured at location 3 MPa
z penetration depth m
α measured total angle between the vertical axis and the axis of the cone penetrometer °
β1 measured angle between the vertical axis and the projection of the axis of the cone penetrometer on a fixed vertical plane °
β2 measured angle between the vertical axis and the projection of the axis of the cone penetrometer on a vertical plane that is perpendicular to the plane of angle β1 °
σvo total overburden stress MPa

ISO 22476-1:2012 Field testing — Part 1: Electrical cone and piezocone penetration test