Chapter 2
CF cone
Cone penetrometers
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Table 1 Subtraction cones | |||
Capacity: | |||
10 tonnes | 15 tonnes | ||
Apex angle of cone | 60° | 60° | |
Diameter | 35.7 mm | 43.8 mm | |
Projected area of cone | 1000 mm2 | 1500 mm2 | |
Length of friction sleeve | 134 mm | 164 mm | |
Area of friction sleeve | 15000 mm2 | 22500 mm2 | |
Maximum force on penetrometer | 100 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 tonnes | 15 tonnes | ||
Apex angle of cone | 60° | 60° | |
Diameter | 35.7 mm | 43.8 mm | |
Projected area of cone | 1000 mm2 | 1500 mm2 | |
Length of friction sleeve | 134 mm | 164 mm | |
Area of friction sleeve | 15000 mm2 | 22500 mm2 | |
Maximum force on penetrometer | 100 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 penetration | 20 mm/sec ± 5 mm/sec | |
Maximum inclination | 15° | |
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 machine | At least 1m from previous CPT, or at least 20 times the diameter of a previous borehole | |
Level of thrust machine | Vertical ± 2° | |
Distance between measurements | maximum 20 mm | |
Calibration | Every 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 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 | |