Seabed Soil Stiffness 1

[JT100]

I am trying to calculate the lateral and vertical stiffness of the seabed, i have done this for clay type soils previously using DNV RP F105 (7.4.10) and I am presently doing some calcs for a seabed made up of sand. The formulas given use the specific mass ratio, diameter and dynamic stiffness factors (lateral and vertical). The dynamic stiffness factors are taken from tables 7.5 (sand) and 7.6 (clay). However when using the values for loose sand the vertical and lateral stiffnesses come out at in the region of 8e5 and 5e5 N/m/m however the clay values are a lot larger at 1.5e7 and 1.0e7 N/m/m which seems a bit stiff, and seems to be messing up my finite element model. Is there any other standards that offer alternative methods of caclualting the soil stiffnesses? thanks.

 

[narenr]

Autopipe and CeasarII programs calculate the soil stiffness internally with basic soil parameters. Refer their manuals which provides very good information.

You could also calculate from DnV RP F109 On-bottom stability code (which supercedes DnV RP E305).

On the other hand you could also derive from fundamentals, refer Bowles textbook. Calculate the pipeline settlement for a given load, determine contact area from pipe geometry, load divided by contact area will give you the soil stiffness. See attachment.

Narendranath R
Pipeline engineering is made easy with state of the art computer software, visit www.narendranath.itgo.com.

 

[JT100]

thats just what i was looking for, and a collegue has that text book. thanks mate

 

[eureka]

See "Guidelines for the Design of Buried Steel Pipe". published by American Lifelines Alliancs and ASCE (American Society of Civil Engineers. If you Google the title, you will find the publication available in PDF format on line. You can download it.