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Re: RR Tie retaining walls

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Kathleen A. O'Brien wrote:
> HI All:
> I have an interesting problem.
> A client wants to put in a wall consisting of Rail Road Ties spanning
> between columns. The columns will probably be fat telephone poles. The RR
> ties will of course be pressure-treated.
> This particular developer did this a decade or so ago, and got it OK'd by
> the City (Thousand Oaks). I took a photo of the existing wall and it looks
> really nice, and appears to have held up quite well. Of course the Code has
> changed a few times since then.
> Questions:
> 1. Does anyone know how easy it would be to get RR ties and telephone
> poles?
> 2. Does anyone have any ideas on what allowable stresses would befor RR
> ties? I would probably assume stresses for redwood if I couldn't get any
> information.
> Thanks for any input
> Kate O'Brien, P.E.
> Simi Valley, CA

This type of wall you are referring to is called soldier pile walls.

You really do not have to be to worried about the stresses in the
railroad ties as long as they are in decent shape. Actually, some
railroads would use these ties to support a 20 foot excavation and the
weight of the train with pile spacing at approximately 8 feet. I do not
have handy the allowable stresses for the ties, but could easily find
them if you want. 

Note that most people agree that not much pressure is applied to the
ties. Arching action transfers the load directly to the piles rather
than to the lagging. 

I would be more worried about the piles. In addition to having adequate
strength, make sure that you have enough embedment to resist overturning
and sliding. You can assume the passive pressure acting on three times
the diameter of the pile. The rule of thumb is that the embedment should
be twice the height of the wall. 

Bruno Côté