It seems that use of the Robertson charts (Robertson, P.K.  " Soil Classification using the cone penetration test" Canadian Geotechnical Journal 27(1), 141-8) to classify soil type based on CPT results is widely accepted practice in the Netherlands. I cannot, however find any prescriptions in the current Eurocode which explicitly allows this. I have checked all relevant standards:
- EN 1997.1
- EN 1997.2
- NEN-EN ISO 22476-1
- ISO 14688-1 and ISO 14688-2
Some of these standards are perhaps not the most recent and others do not contain the national annexes, so perhaps that is my problem. However, I cannot find a clear stipulation which allows or prescribes use of the above charts to actually determine soil type based on CPT results.
Could anyone indicate why this is allowed? Am I missing something in the standard? If it is common practice how does it not contradict the standard?