Precast Block Retaining Structure

[Everynameistaken]

Hello,

I am looking to try and determine the internal sliding resistance of a lock block (precast keyed blocks) wall. These blocks are precast concrete with a small key on the top and they are stacked together.

At the base between the prepared sub grade i would consider a limit states (LRFD) Fr = Phi x (P x tan (2/3 sub grade friction angle)

In-between block layers the sliding resistance is base only on the friction between the blocks.

so again my LSD (LRFD) would be Fr = phi x P x mu,

My question: I am having trouble getting too many sources to have the same value for mu. The "lock Block" design guide notes to use tan 35 = 0.7, but this seems very high,

Thoughts everyone??

 

[JedClampett]

When I've considered these type retaining structures, I was impressed with the engineering manuals produced by the manufacturer. Have you researched those?

 

[TehMightyEngineer]

We manufacture and I design these types of walls a lot; both reinforced MSE segmental walls and "gravity" segmental block walls. They are very complicated and take quite a bit of work to hand calculate. As Jed said, contact the manufacturer and they'll help you out. For what you're looking for, friction tests to ASTM D6916 is the typical way block-to-block frictional strength is determined. Tan 35° sounds about right.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

http://www.americanconcrete.com