Timber Sleeper Retaining Wall 3

[welshsteve]

Hi

I am being tasked with designing a retaining wall, 900mm high for a garden wall, using timber sleepers.

I have no idea how to go about this initially, I can get my soil loadings and moment applied, but not sure where to start with my resistance of this, the client is eager to use sleepers.

Do I use traditional retaining wall design, using self weight of the timber and a small lean mix base to resist this? Or do I need to design the timber for the pressure at the bottom of the wall as a beam spanning between vertical posts?

Some urgent help would be great!!!!

 

[Archie264]

Here you go, look on Sheet 2 & 3

http://www.fairfaxcounty.gov/dpwes/publications/retainingwall/details.pdf

 

[RFreund]

Oh boy,

Step one -> convince the owner to not use a timber wall.
Step two -> use a segmental retaining wall (precast blocks).

We actually don't design these due to their poor performance. But if I were to -> draw your pressure diagram due to soil and surcharge, then find a load path. I assume sleepers are deadman/tieback, right? Are you planning on designing a soildier pile with tie-back type system?

Do I use traditional retaining wall design, using self weight of the timber and a small lean mix base to resist this?

This is a short wall but the dead load of the timbers is pretty small. I'm not sure what you mean by base?

Or do I need to design the timber for the pressure at the bottom of the wall as a beam spanning between vertical posts?

That sounds reasonable, but I'm sure they will be upset about digging the holes for the posts.

EIT

http://www.HowToEngineer.com

 

[welshsteve]

Much obliged.

RFreund - I'm in a monumental battle, google has caused a war, he is a keyboard warrior (like myself now!) and found walls that have been used and is adamant he wants us to design it this way, no matter how I fight he keeps going back to these examples.

As a base I mean a small concrete plinth to build up off, nothing structural as such, but would provide some dead load, with posts cast in to this base to the rear. They are happy to have posts which is mad.

I have looked at deadmans/tie backs and would specify them, although I think he is going to be a nightmare client, because it "may cost more"!

 

[msquared48]

Run. Let him do it himself and deal with the jurisdiction.

Mike McCann
MMC Engineering

 

[RFreund]

While I'm still against this. And believe me they're are no good examples. Sure maybe the day after they are put in. Having said that...
If the are ok to dig posts then design it as a soldier pile and lagging wall. They will probably have to embed the posts say 6'-8' oc about 1.5xH - 2xH in the ground and maybe even in concrete or some sort of pier. If you add a tie back then this embedment could be shorter. Make sure you design the connections for the appropriate pressure (near the base of the wall should be worst case). Also design the lagging to span between posts. Make sure to put some sort of drainage aggreate and perferated drain pipe wrapped in filter fabric or something to this effect.

Again I'm just not a fan of timber walls but maybe there is a place for them.
Actually it's probably not a bad idea to put in a longer tie back, this way when they have to rip it out there is room to install a proper wall...

EIT

http://www.HowToEngineer.com

 

[welshsteve]

Thanks RFreund, this is the approach I have now considered. The client has reduced the wall to 800mm which helps and I have told him he must use Jarrah sleepers, 300mm deep with posts concreted into a base behind the wall and tie backs throughout.

I'm not happy with it, though I have justified it as mentioned designing as a timber beam spanning between posts for the pressure applied at the bottom of the wall. With tie backs included the effective length should only be about 900mm in total so I'm reasonably satisfied. And yes, I would love him to change his mind and put a proper wall in.

 

[Splitrings]

I have got to be missing something. We are talking about a 3' high retaining wall for a garden? He must have a massive tractor if this can't be done with wood. Its done all the time with 6x6 or 8x8 timbers. The tiebacks don't have to be timber, they could a duckbill type anchor or any other deadman. Is there a jurisdiction that requires these be engineered?

 

[msquared48]

I thought that according to the IBC, or IRC, a wall had to be engineered only if it was greater than 4 feet in height.

Mike McCann
MMC Engineering

 

[ztengguy]

I was wondering the same thing, its a 3' wall, not sure what the problem is?

 

[SLTA]

Wood retaining walls fail fast and mean around here. They are the local geotech's bread and butter. I think that may be the issue.

 

[RFreund]

Oh well for some reason I was thinking it was 6' tall, that whole metric thing....
Either way, still not a fan of timber. But I understand at 3' tall there's not much of a threat for injury.

EIT

http://www.HowToEngineer.com