Page "Cone penetration test" Paragraph 4
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The original cone penetrometers involved simple mechanical measurements of the total penetration resistance to pushing a tool with a conical tip into the soil.
Different methods were employed to separate the total measured resistance into components generated by the conical tip ( the " tip friction ") and friction generated by the rod string.
A friction sleeve was added to quantify this component of the friction and aid in determining soil cohesive strength in the 1960s.
Most modern electronic CPT cones now also employ a pressure transducer with a filter to gather pore water pressure data.
The filter is usually located either on the cone tip ( the so-called U1 position ), immediately behind the cone tip ( the most common U2 position ) or behind the friction sleeve ( U3 position ).
Pore water pressure data aids determining stratigraphy and is primarily used to correct tip friction values for those effects.
CPT and CPTU testing equipment generally advances the cone using hydraulic rams mounted on either a heavily ballasted vehicle or using screwed-in anchors as a counter-force.
One advantage of CPT over the Standard Penetration Test ( SPT ) is a more continuous profile of soil parameters, with CPTU data recorded typically at 2cm intervals.
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