Offshore Pipeline: soil liquefaction

[robb4]

Hi,

I'm collecting input data for a Detail offshore pipeline project.

Regarding the soil liquefaction analysis due to seismic hazard I'm collecting data regarding Peak Ground Acceleration assosiaceted with return period of 200, 500 and 1000 years.

My question is which is return period to be considered during design for seismic load?
Is there any standard or guidelines to be followed?

Thanks

 

[BigInch]

100 might be sufficient; check your design code. If there is none there, see if DNV 109 has any recommendations.

You can also get liquifaction from wave cycle frequencies and pressures, so your wave height and water depth may play a part in that analysis.

 

[SFLM]

robb4,

200, 500 or 1000 seems to be too much for a pipeline which lasts 30 years usually. In addition, you need to know the water depth since at some depth, waves no longer have influence. You can define this in DNV-RP-F105.

Cheers,
Steve

 

[robb4]

Thanks for your reply.

Of course the wave is another aspects to be considered in liquefaction study but considering my water depth (60m) maybe it wouldn't be an issue.

Regarding the return period the only one reference I find is on DNV OS F101 that states the following (Sec 4 C500):

C 500 Earthquake
501 Load imposed by earth quake, either directly or indirectly (e.g. due to failure of pipeline gravel supports), shall be classified into accidental or environmental loads, depending on the probability of earthquake occurrence in line with accidental loads in F.
Guidance note:
Earth quake with 475 years return period may be taken from International seismic zonation charts as in Eurocode 8. This can then be converted by importance factors to 100 years return period.

I think it is enough in order to use 100 year.

Regards
Robb4