Calculation of porewater response - eurocode 7

[hwg89]

Trying to get to grips with the new eurocode 7:

Think fill on soft clay.
In undrained stability analysis with effective stress parameters.
How do you calculate the porewater pressure response the right way according to eurocode 7 ?
How much conservatism is normal and right to applie in the choice of characteristic parameter(s), like Skempton B-parameter ?

 

[Mccoy]

hwg,
your question is not very clear to me.

Do you mean getting undrained parameters (Su) from a drained TX test with pore pressure measures?

If so, I'm not sure using characteristic values for Skempton parameters would be the right procedure.

What I'd do would be to determine Su first using an average values of all the parameters involved and then transform it to characteristic value Su_k.

 

[YannisChasiotis]

Why do you need to change from pre-EC technique? My opinion is to use the same amount of conservatism...

 

[YannisChasiotis]

@Mccoy: He doesn't want to work with su. Intead he wants to work with c', ?' and the anticipated pore water pressure build up...

 

[Mccoy]

Why do you need to change from pre-EC technique? My opinion is to use the same amount of conservatism...

Actually, eurocode 7 requires that geotechnical parameters are used as conservative estimates of the value which governs the occurrence of the limit state. That's a must.
You may end up with the same amount of conservatism though, if some conditions are fulfilled.

@Mccoy: He doesn't want to work with su. Intead he wants to work with c', ?' and the anticipated pore water pressure build up...

OK, I missed that, I would say that if pore pressure is used to compute phi-c, then a conservative estimate of phi and c should be used as characteristic values leaving unchanged the value of the skempton parameters.
Usually the geotechnical parameters directly used in the limit states formulas are transformed into characteristic, then design values.

I'll check this though, wether there is some specific example available from the few authoritative references