Geotechnical Data and Pile Design - Offshore Structures: Design, Construction and Maintenance - page 226

During actual testing with wire-line tools, the data-acquisition system
should allow for real-time inspection of the measured results, in both digital
and graphical form.
The measured results should be stored digitally for subsequent processing.

Calibration Requirements
For each cone penetrometer, an accurate calibration should be made of the area
ratios of the cone and the friction sleeve, as given in IRTP (1999) . These values
are characteristics for each cone penetrometer and should be documented in
each field report, because they are very important for data reduction. The cali-
brations should be checked at least once a year.
Calibrations of each sensor should be made prior to each project and at least
every third month or after about 100 soundings. If the load cells have been
loaded close to maximum capacity, new calibrations should be carried out.
During field work, regular function checks of the cone penetrometer and
measuring system should be carried out. As discussed above, offshore soil
investigation is very expensive, so it is important to follow the calibration pro-
cedure for any tools before use. The owner ' s representative should check this

with the contractor.
A calibration certificate for each cone penetrometer should be presented
before mobilization.
For each cone or CPTU representative of each type (i.e., of the same load
cell capacity), the following temperature calibration should be documented to
have been done at least once:

Variation of response to zero load for temperatures varying from 0 ° C

●

to 40 ° C

Calibration factor of each sensor at a temperature of +5 ° C; the method used

●

to obtain the calibration factors should be explained.

The use of accuracy classes, as required in IRTP (1999) , should be adopted.
Equipment and procedures to be used should be selected according to the required
accuracy class given in Table 4.1 . These precautions are very critical and it is
important that they be considered and monitored by the project quality team.
If all possible sources of errors are added, the accuracy of the recordings
should be better than the largest of the values given in Table 4.1 . The relative
or percent accuracy applies to the measured value and not the measuring range
or sensor capacity.
Class 1 is meant for situations where the results will be used for precise
evaluation of stratification and soil type as well as parameter interpretation in
profiles including soft or loose soils.
For Class 3, the results should only be used for stratification and for
parameter evaluation in stiff or dense soils. Class 2 may be considered more
appropriate for stiff clays and sands.