Sea Bottom Static Friction Coefficient

[phasteddy]

I'm calculating the mooring capacity of concrete anchor blocks lain on the sea bottom. I've seen a range of coefficients used, from 0.6 to 0.75. Is there a good reference out there from which I can find some lateral static friction values for different types of sea bottoms?

 

[jdonville]

phasteddy,

I'm no expert, but I would imagine that the US Naval Facilities Engineering Command (NAVFAC) or USACOE might have something (it being quite on-topic for them). The US armed forces have been repackaging and updating many of the engineering design manuals as UFC documents lately.

You should look for military design references for concrete, rip rap or large sized rock placed in marine environments (for causeways, breakwaters, cofferdams, piers, jettys, drydocks, etc). Most of these will probably be for shallow-water applications, though.

The old NAVFAC DM 7.02 (no longer available for download from the Navy - vulcanhammer.net is the only source I am aware of) has recommended friction values for mass concrete on many types of soil.

You may have to reduce the weight of the blocks before calculating the static friction if there is an upward pull on the block.

Hope this helps,

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

 

[phasteddy]

jdonville,
I looked at the NAVFAC DM 7.02. Table 1 on page 7.2-63 has some info I can use. In addition to friction, dependent on bottom sediment composition, cohesion might increase the resisting force of the concrete anchor. Thanks for your help.

 

[jdonville]

phasteddy,

Don't count on cohesion. The friction angles in DM7.02 are given for nominally cohesive soils, too. Use the reduced friction angle for cohesive soils to be safe.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com