Geotechnical Data and Pile Design - Offshore Structures: Design, Construction and Maintenance - page 225

Equipment Requirements
The geometry of the cone penetrometer, with tip, sleeve and pore pressure filters,
should follow IRTP (1999) , from which the following is extracted: 1) the pene-
trometer tip and adjoining rods should have the same diameter for at least
400 mm behind the tip, and 2) the cone should have a nominal cross-section
area, Ac, of 1000 mm 2 , with 35.3 mm

h c ≤
31.2 mm, where d c is the cone diameter and h c is the height of the conical part.
According to the IRTP (1999) , cone penetrometers with a diameter between
25 mm (Ac = 500 mm 2 ) and 50 mm (Ac =2000mm 2 ) are permitted for special
purposes, without the application of correction factors. The recommended
geometry and tolerances given for the 1000 mm 2 cone penetrometer should
be adjusted proportionally to the diameter.

≤ d c ≤ 36.0 mm and 24.0 mm ≤

CPT Testing Procedure
The testing procedure should comply with the IRTP (1999) as follows:

The nominal rate of penetration should be 20 mm/s with an accuracy of
±

●

5 mm/s.

The length of each stroke should be as long as possible, with due considera-
tion of the mechanical and strength limitations of the equipment, noting that
continuous penetration is preferred.

●

Readings of all channels should be taken at least once per second (for every
20 mm of penetration).

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For quality control, zero readings should be recorded before and after each test.

●

For CPTU testing, the filter stones should be fully saturated and the pore
pressure measurement system should give an instantaneous response to changes
in pressure. Documented procedure for saturation of filter stones should be
available.
Pore pressure dissipation tests should be carried out to at least 50% con-
solidation (i.e., halfway between pore pressure after stopping penetration of
the cone and the assessed in-situ pore pressure). In cases where this may
imply long measurement periods, the client and the contractor should agree
on the maximum test duration, depending on the importance of the results.
The sampling rate during a dissipation test should be at least:

During the first minute, 2 times each second ●

Between the first minute and tenth minute, once each second

●

Between 10th and 100th minutes, once every 2 seconds

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After 100 minutes, once every 5 seconds

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The data-acquisition system should be such that overall accuracy is
maintained.
The resolution of the measured results should be within 2% of the measured
value.