Cone Penetration Testing (CPT)

Cone penetration testing (CPT) represents a sophisticated penetration test method which can be used to rapidly obtain information on variations in soil type and properties with depth.

The equipment comprises an instrumented cone (containing the electronics), which is pushed into the ground via steel rods using a CPT rig. The test provides near continuous records of penetration resistance (cone tip and friction sleeve) and dynamic porewater pressure (where using the piezocone).

Post processing of the data is carried out to derive (according to soil type):

• Soil type
• Shear strength
• Angle of friction
• Relative density
• Equivalent SPT N value
• Coefficient of consolidation (from dissipation tests using piezocone)

SOCOTEC has a range of CPT rigs to suit site access and testing requirements. These include truck mounted plant for drive-on site access, tracked machines of various sizes for more challenging terrain and specialist modular rigs for use in restricted access locations and on jack-up platforms, for example.

Productivity rates for CPT are high compared to conventional borehole methods, between 100 and 150 m of testing is achievable in a day, subject to suitable ground conditions and access. This allows for rapid collection of large amounts of data. Maximum penetration depths vary depending on ground conditions but up to 40 m can be achieved with standard equipment.

Field data can be provided on completion of each test and processed data within 24 hours. The data can also be reported in AGS4 digital format.

A variety of other cone types and techniques are available from SOCOTEC, including soil samplers, to suit various testing requirements in different ground conditions:
• Cone Pressuremeter – strength and stiffness
• Seismic Cone – shear and compressional wave velocity, used to calculate elastic parameters including small strain shear modulus, Go
• Field Vane - shear strength
• Flat (Marchetti) Dilatometer - correlation with various engineering parameters
• Mostap Sampling – recovery of low disturbance push-in samples

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