Terraced/Tiered Cantilever Retaining Walls 1

[mschwike]

Does anybody know how to determine the surcharge loads for conventional masonry retaining walls that are terraced. What I have is four 5' high masonry walls 4' apart. How much surcharge is transferred from one wall down to the next, and do these load accumulate down to the bottom wall? I have been reading up on the Boussinesq equation but this doesn't seem to consider the lateral aspects of the load; or is there a conversion? I am using enercalc, but the manual has a disclaimer indicating that the Boussinesq analysis may be used for the vertical load applied to the soil from the adjacent footing, however the design must also consider the lateral sliding loads from the adjacent wall. This load could be applied as "added lateral load ", however this is at the discretion of the designer and is not within the scope of the program.

 

[BAretired]

I believe it would be similar to a cantilever retaining wall with sloping surcharge, but perhaps it would be best if you could provide a cross section through the four walls indicating grade elevations at all locations.

BA

 

[MiketheEngineer]

Versa-Lok has some real good info out there. I tend to follow it even for solid concrete retaining walls. But when I have choice I would use them and their engineering any day!!

 

[asixth]

Treat as sloping backfill with 5V:4H. This will increase the active earth pressure against the wall significantly.

 

[RFreund]

There a couple different approaches that can be taken. Because we are talking about internal stability, sliding and overturning. The upper wall can really be handled as an 'offset surcharge'.
Unless you are relying on passive pressure, the horizontal force required to resist sliding is usually not a consideration although I guess it could be. That force could also be handled with elastic methods. A good reference you may be interested in is: Basics of Retaining Wall Design, 9th Edition: Hugh Brooks, John

1.) Elastic methods (i.e. bousinessq strip load) - use your bearing pressure. You want to use a 'mayerhof' bearing pressure distribution to get the strip footing 'surcharge'.
2.) Equivalent backslope as previously mentioned.
3.) A trial wedge method, possibly.

Alternatively you may even want to consider using a segmental wall (i.e. versa-lok) they are usually cheaper to install. If you do decide to use a segmental wall NCMA has an approximate approach for determining pressures for tiered walls. You may be able to use it but you have a 'rigid' wall system and those equations were really derived for 'flexible' wall systems. However IMO they are semi conservative and could possibly be used.

EIT

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