DnV RP-E305 Soil data

[pipeline058]

As per DNV-PR-E305, the soil is divided to "Sand" and "Clay", and for sand, friction factor of 0.7 is advised.
So, what about Silt, or even more mixed conditions like "Silty Sand"?
AGA suggests for decreasing the friction angle with 5 degree if there is "find sand" or silt in the soil exceeding 5%.

DNV-RP-F109 is also suggesting friction factor of 0.6 for sands.

Actually I am looking for a proof to not using 0.7 for "silty Sand", while I am using E305. Is there any reference questioning E305 sand model?

 

[BigInch]

Are they not suggesting that the same 5 deg reduction be used for clay. Is not clay = silt with no sand?

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"The problem isn't finding the solution, its trying to get to the real question." BigInch

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[Eyeoftheneedle]

DNV-RP-E305 (now superseded by DNV-RP-F109) is very specific in that if you are using the Simplified Design Method then you must use 0.7 for sand and Figure 5.11 for Clay. The reason for this is because it is not just a friction factor, it is also a calibration factor that helps you get conservative results as opposed to using the Generalised Design Method in the same Code.

Be careful not to 'cherry-pick' values for factors from different Codes as quite often the factors have double uses to make that Code's formulae work correctly.

In short, if you want to use E305 and you have predominantly sand then you have no choice but use 0.7.