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Lankelma is the foremost contractor for onshore in-situ soil testing in the UK. An acknowledged specialist in CPT, Lankelma also offers a worldwide consultancy and training service.

A.P. van den Berg develops, designs and manufactures geotechnical and environmental soil investigation equipment for onshore and offshore applications. Specialists in CPT systems and equipment.

Gardline

Gardline Geosciences offers worldwide marine geotechnics, in-house consutancy and services with marine investigations ranging from nearshore to full ocean depth (down to 3000m).

About the Author

Hans Brouwer studied civil engineering at Delft University in The Netherlands. He has worked as a part-time lecturer at Amsterdam Polytechnic and was senior partner in a structural engineering consultancy. He has written a standard textbook in Dutch about the design of building foundations. He now lives in England where he writes technical textbooks in English, hopefully to reach a bigger readership.

Chapter 2

CF cone

Cone penetrometers

 


CONE PENETROMETERS 2.1

Cone penetrometers can be divided into subtraction cones and
compression cones.

  • A subtraction cone measures the total force on the penetrometer
    (sleeve + tip) and the tip resistance. The sleeve friction is calculated
    by subtracting the tip resistance from the total force
  • A compression cone measures the tip resistance and the sleeve
    friction separately. This results in a lower max value (1 MPa) for the
    sleeve friction.


There is no restriction for the sleeve friction of the subtraction cone.
The only restriction is the total force on the penetrometer. For the UK it
is best to use subtraction cones because a sleeve friction higher than
1 MPa is common, especially in very stiff clay.

There are cone penetrometers with 10 and 15 tonnes capacity.
Tables 1, 2 and 3 give specifications for both cone capacities.


 Table 1 Subtraction cones
  Capacity: 
  10 tonnes15 tonnes
 Apex angle of cone 60°60°
 Diameter35.7 mm 43.8 mm
 Projected area of cone 1000 mm2 1500 mm2
 Length of friction sleeve134 mm 164 mm
 Area of friction sleeve15000 mm2 22500 mm2
 Maximum force on penetrometer100 kN 150 kN
 Maximum cone resistance, qc (if fs = 0) 100 MPa (100 kN) 100 MPa (150 kN)
 Maximum sleeve friction, fs (if qc = 0) 6.6 MPa (100 kN) 6.6 MPa (150 kN)
 Diameter of push rods 36 mm 36 mm

 Table 2 Compression cones
  Capacity: 
  10 tonnes15 tonnes
 Apex angle of cone 60°60°
 Diameter35.7 mm 43.8 mm
 Projected area of cone 1000 mm2 1500 mm2
 Length of friction sleeve134 mm 164 mm
 Area of friction sleeve15000 mm2 22500 mm2
 Maximum force on penetrometer100 kN 150 kN
 Maximum cone resistance, qc (if fs = 0) 100 MPa (100 kN) 100 MPa (150 kN)
 Maximum sleeve friction, fs (if qc = 0) 1 MPa (15 kN) 1 MPa (22.5 kN)
 Diameter of push rods 36 mm 36 mm

 Subtraction cones are stronger than compression cones because they
have a stronger construction due to there being no strain gauges to
measure the sleeve friction. In practice the cone penetration tests will
be stopped at a maximum sleeve friction of 2 MPa.

 Table 3 General information
   
 Rate of penetration20 mm/sec ± 5 mm/sec
 
 Maximum inclination15°
 
 Sensors Cone resistance
Sleeve friction
Inclination
Depth

Porewater pressure (only for CPTU) with a maximum reach of 1, 2 or 5 MPa. In the UK, porewatre measurements up to 2 MPa are common, especially in chalk and clay
 
 Position of thrust machineAt least 1m from previous CPT, or at least 20 times the diameter of a previous borehole
 
 Level of thrust machine Vertical ± 2°
 
 Distance between measurementsmaximum 20 mm
 
 CalibrationEvery 3 months or 3000m of sounding
 
 Field checks See Chapter 7, 7.2 Fieldwork, Table 5
 
 Maximum wear Angle of cone: 60° ± 5°
Sleeve: 35.7 mm ± 0.4 mm
 
 Symbols used on some cone calibration certificates

C10 = 10 tonnes compression cone
C15 = 15 tonnes compression cone
S10 = 10 tonnes subtraction cone
S15 = 15 tonnes subtraction cone


C = measurement of cone (tip) resistance
F = measurement of sleeve friction
P = measurement of porewater pressure
I = inclination
S = seismic cone


Example Cone number S10-CF.038 means 10 tonnes subtraction cone, number 038, with measurement of tip resistance and sleeve friction
 
 
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