Reinforce Existing Wood Retaining Wall 1

[bbengineering]

I have a friend who went ahead and built a 5' high railroad tie wall without any permits. Well, the town got involved and now obviously wants it certified by an engineer. It was built with almost no reinforcement. Any suggestions on how to reinforce the wall sufficiently? I can't find any resources anywhere for design of wood walls.

Bryan Nesteriak, P.E.
B&B Engineering

http://www.bbengrs.com

 

[cvg]

take it down and rebuild it?
build the retaining wall using concrete. Place the railroad ties in front to cover up the concrete

 

[msquared48]

Place 4X6 at 4' or so opposite the soil face in augered holes filled with concrete along it's length and show that the rr ties and posts can take the soil load. Probably will need 2 to 2.5 feet of auger depth.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[SlideRuleEra]

"Timber Retaining Walls for Residential Applications"

http://www.finelinetimbers.com.au/pdfs/Retaining Walls.pdf

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[PEinc]

Without details of the as-built wall, it is not possible to give you any advice. The comments about wall reinforcement are meaningless without knowing the wall construction. Timber tie wall are not "reinforced." They usually are bin-like structures with a timber facing and perpendicular timber tie deadmen. There is no reinforcement. The problem with these walls is usually their lack of, or insufficient number or length of, the perpendicular timber deadmen.

The information that SlideRule Era attached seems to deal with vertical, cantilevered, timber soldier beams with horizontal lagging. I would be surprised if that is how the subject wall was constructed.

http://www.PeirceEngineering.com

 

[PEinc]

Here is an old paper on timber retaining walls, bulkheads, and seawalls.

www.PeirceEngineering.com

 

[bbengineering]

Thanks for all of the constructive comments. Here is a little more info if it helps:

The wall was constructed with 6x6 P.T lumber and stacked it like a typical residential railroad tie wall. Every 10' he installed 2 perpendicular ties back to a 3' long 6x6. I am exploring to see if I can add additional support since it obviously doesn't meet the standard criteria as it is so he doesn't have to remove and rebuild.

 

[oldestguy]

I'm wondering if he could contact an electrical contractor that owns a utility auger that is mounted on a truck so that it can lay almost horizontal, or at least say 30 degrees above the horizontal.

First drill some holes in front and set vertical posts say 4 feet deep- with tops at the wall top, maybe two posts together.

Then, where those vertical posts are added in front he ought to be able to install those utility pole anchors at some slight angle from the horizontal from near the top of the wall set sufficiently far back to provide anchorage. Tie them to those vertical posts.

The Chance anchor company may have some guidelines as to what capacity can be developed per anchor. A geotech engineer could calculate it knowing the soil conditions.

Of course the structural evaluation of the wall horizontal membersalso is involved.

 

[Geostructsparks]

If you can excavate at the top of the wall a foot or two, install a geogrid or strength geotextile layer anchored to the back of the PT timber. With a 5' wall, it should nearly be possible to design a single-layer MSE wall, the tail may just have to be a little long, or have an anchor trench. I have repaired/replaced at least one 1-strap geotextile wall, but that wall had other problems, so it may work. The strap at 1' from the top will need some method to tie to the wall, and the wall timber it attaches to will be poorly-confined, so you probably ought to bolt the top of the retaining wall vertically with really long lag bolts to tie it all together. Not sure if this is less effort than bracing the front, but you can probably make it calc.

This assumes its less invasive to remove a few timbers from the top of the wall than to drill at the base of the wall.

 

[RRPC]

i have a very similar situation with a client. An unstable 6x6 timber wall, 6 feet tall, sloping backfill at 25% grade, built without a permit.
'Chance anchors' are soil nails which is mechanically stabilized earth (MSE) system. Embedment depth about 8' and spacing 2 rows at 4 feet, $300 - $500 per, plus strengthening of wall face. I don't have confidence in the longevity of the helical steel plate anchors.
Deadman anchors (tiebacks) need to be grouted to full bond length beyond the slope failure plane, about 15 feet or more, specialty equipment required, local company (Virginia) JES does a lot of these for basement walls, cost about $1000 per, spacing 2 rows at 8 feet. Load testing required, long term creep is a problem in soft cohesive soils.
I considered concrete buttresses in front of the wall. this saves some concrete material but the 'reverse cantilever' footing still needs to be continuous along length of wall and reqiures more width than a regular cantilevered footing under the wall.
I'm currently considering simply grading for a sloped embankment, no wall, but we may not have adequate room.
Also am looking at a wood 'crib' wall which will salvage a lot of the existing wood material. The crib wall design is another form of the MSE system seen with geogrids and soil nails.

HTH,
David