Wooden fence retaining wall 3

[Aussie Dave]

Hi All,

I am currently working on a wooden fence post retaining wall solution designed by an Architect attached. I have been asked to calculate the attached, the problem is that I have calculated sheet piling using Gross Pressure Method in the past, but I am not sure if I can calculate the wooden posts in the same way. Does anyone know which method would be best to calculate a wooden retaining wall as attached or should I use something different such as a concrete retaining solution with a wooden fence on top?

 

[MTNClimber]

You would be looking at calculating the loading the same way you would with a soldier pile and lagging wall which is similar to sheet piles except with the added tributary area approach. There's plenty of literature out there for soldier pile and lagging walls. Everything I have references US Imperial units. Maybe do a little digging online.

 

[PEinc]

Agreed. Don't forget to add more lateral loading due to forces (wind, snow, etc.) acting on the fence.

http://www.PeirceEngineering.com

 

[Aussie Dave]

Thanks for everyone's help.
Can I use timber posts as suggested by the Architect to drive into the ground similar to soldier piles?

 

[JoshPlumSE]

Am I the only one who hates the idea of using wood for piles or retaining walls? I know it can be done. It's just leaving wood in contact with soil always irks me.

 

[MTNClimber]

I haven't used timber posts in this application so I'm not sure if it will work. But you would be looking at drilling a hole to the required tip elevation, dropping the pile or post in the hole and using flowfill, concrete, or grout to fill the hole.

 

[Aussie Dave]

That is another good idea, does anyone know how to calculate the tip elevation for a timber post using flowfill concrete to fix posts into the ground similar to attached drawing?

 

[jayrod12]

Wood in contact with soil does not bother me one bit. But, wood subjected to constant wetting and drying at the interface does. People's fence posts always rot out at the ground interface.

 

[Aussie Dave]

I see what you mean Jayrod12, but you can treat the posts or include a membrane around the post to avoid rot.

 

[r13]

Form the upper end of the bore holes, and bring the concrete fill/grout a few inches above ground. The architect shouldn't object to it.

 

[XR250]

I believe you will save the owner money in the long run by designing a masonry or concrete retaining wall - something that will last as long as their substation.
You could bolt the fence to the face of the wall so it can be replaced when it rots

 

[dhengr]

Aussie Dave:
You want a high retention percentage of the pressure treatment for longevity for this type of application, not treated lumber that you might buy at a big box store. This will likely have some adverse effect on your hardware. The 200x100mm posts may be kinda undersized, at 100mm, in their important canti. bending direction. You want the strongest member orientation to react the soil pressure. You might be better off using larger post sections at a uniform spacing, and embedded in the concrete, in the drilled holes. Slope the top of the conc. to drain away from the posts, and slather the top of the conc. and bot. of the posts with some asphaltic material to kinda keep some water out of the top of the conc. and away from the joint with the post. Make your lagging up as modular units of horiz. 200x100mm members of a height to retain the soil, and with vert. members at each end of these modular units, lapping the horiz. pieces. These units will be about 4000mm/3=1333mm wide, center to center of the posts. Detailed properly, the vert. end pieces will accept the vert. screening pieces too, all as a prefabed unit. Then, the entire 1330 unit would be fixed to the back of the posts. There would be nine of these prefabed units in your current scheme.

I also agree with XR250 that you might be better off making the earth retention portion of this out of masonry or concrete. Then, the top screening portion can be wooden. The uphill soil should be sloped to drain to both sides of the enclosure, and some drain tile should be installed, on three sides, to drain to daylight at the front of the enclosure.

 

[r13]

Just some side issues to check. Does the substation (seems enclosed) posses fire hazard? If so, does the wood fence qualifies as a fire wall?

 

[PEinc]

I don't like permanent retaining walls with exposed timber lagging. I certainly don't like, and would not use, timber soldier beams, even if pressure treated. Build a non-wood wall and, if required, dress it up with an attached wood facade.

http://www.PeirceEngineering.com

 

[Aussie Dave]

Thanks, everyone for the comments. I think that it is probably best to use a concrete or brick structure below ground for the retaining part of the structure with a wooden fence attached above ground to the retaining wall as suggested in the comments. Good point retired13 the substation is completely protected by a GRP cover, so the fence above ground is not required to be a firewall.

 

[dhengr]

Aussie Dave:
Reread what we said, none of us said brick found. Clay brick, at least, does not work at all well being in contact with the soil, it expands and moves and goes to hell quickly. Use concrete or conc. blk., maybe grouted and reinforced for the found. walls.

 

[Aussie Dave]

Thanks dhengr good point.

 

[Tomfh]

Not a fan of timber retaining walls - particularly not timber soldiers.

Our area is hilly and there are countless timber walls. Mainly Koppers log walls. Many are failing, with various bits of strapping etc in an attempt to hold them together. If you’re building a wall do it properly. Something inherently robust and stable.