PDA

View Full Version : Retaining wall advice (deadman locations)


Boobs McGee
06-23-2011, 10:13 PM
Designing a retaining wall for some friends, and was hoping for a little advice.

Basically, they want a 3-4' wall around three sides of a sandbox...kind of like this


_____________________
l l
l l
l l
l l
l l

It's going to be constructed using treated 6x6's (personally, I don't know if they've made safety progressions in the treated lumber world, so I'm not sure if it's safe for kids in terms of splinters and whatnot, so if anyone has any idea feel free to chime in).

My BIG question is, how many deadman am I going to need in the back wall? (the "solid line" in my "illustration" haha) It's going to be 4' tall, and it's holding back some good ol' fashioned colorado soil...which here in the front range, has a LOT of clay. Anywho, I've heard that after your first course of timber, a sensible amount of deadman are: every third row, and 8 foot of spacing. Since the back wall is about 15 feet long, and 4 feet tall, I'm thinking a total of 4 deadman? 2 on the third row, and two on the second to top row?

The hill doesn't have a very steep grade, maybe 5 or 6 degrees?

Does anyone know if 4 of those will be overkill? And also, should they be staggered, or can they be vertically aligned?

Lastly, the side walls are going to gradually build from the first course up to the top...so I was thinking one deadman per side at about the 3' mark.

Cheers and thanks!

Oh, and the walls are about 10 ft long.

Boobs McGee
06-23-2011, 10:15 PM
Aaaand my drawing was "corrected" by the internetz....imagine that second row of vertical lines is on the OTHER side of the solid dotted line. Like an open ended rectangle

enjolras
06-23-2011, 10:39 PM
I did a similar wall with 3 deadmen along the 3rd course over about the same length.

I do have to ask... what are you doing for drainage? If your running any type of drain (which I strongly suggest) behind it, you need to consider that in your placement of the deadmen. They tend to get in the way:)

Boobs McGee
06-23-2011, 10:45 PM
I did a similar wall with 3 deadmen along the 3rd course over about the same length.

I do have to ask... what are you doing for drainage? If your running any type of drain (which I strongly suggest) behind it, you need to consider that in your placement of the deadmen. They tend to get in the way:)

I was thinking some crushed gravel...about a foot or so behind the timbers all the way around. Layer of stone about 18 inches wide, then first course of timber (leaving about a foot or so of rock exposed), then some perf pipe on top of that? Should I fill that entire 12" gap with rock all the way up to the top of the wall?

As far as the deadmen go, how's your wall holding up? Did you only use the 3 deadmen on a 4' wall? Any on the sides, or just the back?

OH, and what did you do for vertical lean. They want a flush vertical face, but I've heard that a slope (1/2" back towards the hill with each course) is structurally more sound. It's only 4', so I didn't know if that mattered ;D

thanks for the response btw!

Bronco Yoda
06-23-2011, 11:00 PM
I prefer K-blocks with pins. 95 lbs. a piece. Much safer and easier to put in once you get the bottom level. But to each their own. THIS WAY YOU WON'T NEED DEADMEN.

Don't forget to put landscaping preen between the dirt and rocks and wrap any pipes for drainage with it so it won't get gummed up later. You can't over do the drainage. Hydrostatic pressure will doom you.

I put in a 5 foot wall 150 foot long a couple years ago. At the end I curved it into a half circle for the kids sandpit. I've been happy with the textured blocks. No splinters, no toxic chemicals. it wont fade or rot.

A whole lot of work but worth it. good luck.

enjolras
06-23-2011, 11:09 PM
I was thinking some crushed gravel...about a foot or so behind the timbers all the way around. Layer of stone about 18 inches wide, then first course of timber (leaving about a foot or so of rock exposed), then some perf pipe on top of that? Should I fill that entire 12" gap with rock all the way up to the top of the wall?

More or less. The only thing I'd add is wrapping the rock about 3/4 of the way up with landscape fabric.

Essentially I dug out the wall about 2' behind the actual wall location and a few inches below it. I laid out long strips of landscape fabric across the bottom of that and put some pea gravel over that to establish a nice base. I laid the first course of the wall and drove 3' of rebar through it about every 16" to anchor it. I then did the second course using landscape stakes to secure it.

I then backfilled that 2' section with river rock and laid out my drain pipe being REALLY careful to ensure that it had a constant downward slope. I then installed the deadmen over that and made sure they were nice and secure. I then finished the wall (again with landscape stakes on every course). I backfilled up to about 6" short of the top of the wall and wrapped the landscape fabric I had laid out earlier BACK OVER the rock. This way dirt and stuff can't work it's way down into my perforated pipe and clog it.

I then put some top soil over that and planted grass:)

As far as the deadmen go, how's your wall holding up? Did you only use the 3 deadmen on a 4' wall? Any on the sides, or just the back?

It's REALLY solid. I do box jumps on it when I work out actually:) It's about 2 years old and besides some mild drying out it's in perfect shape. Good drainage is really the key to these things.

OH, and what did you do for vertical lean[. They want a flush vertical face, but I've heard that a slope (1/2" back towards the hill with each course) is structurally more sound. It's only 4', so I didn't know if that mattered ;D

thanks for the response btw!

It's not just more sound but it's absolutely essential. Retaining walls derive their strength from the force of the ground they are, uhm, retaining. Newtons third law is in full effect here. A perpendicular wall is going to be significantly less strong.

*edit: I should note, that even a 4' wall is bracing against HUGE amounts of force from the soil behind it. I forget the actual calculation, but the force it will be retaining is very significant. Even on a short wall, that integrity really matters.

That said, the lean isn't going to be terrible noticeable. On mine you'd probably never really guess that it actually tilts back into the hill. On a relatively short wall like we're talking, they'll never know.

Boobs McGee
06-23-2011, 11:21 PM
@ yoda, thanks for the suggestion! I've built retaining walls with block before (not the kind YOU used), and I prefer them as well. Sounds like you really have quite the solid setup! They already have the lumber, or else id try to convince them otherwise.

@ enjolras, great ideas. That's EXACTLY what I was looking for! Thanks for taking the time with all of the details...I'm going over tomorrow, so we'll see what they think.

Cheers and thanks again

Bronco Yoda
06-23-2011, 11:59 PM
@ yoda, thanks for the suggestion! I've built retaining walls with block before (not the kind YOU used), and I prefer them as well. Sounds like you really have quite the solid setup! They already have the lumber, or else id try to convince them otherwise.

@ enjolras, great ideas. That's EXACTLY what I was looking for! Thanks for taking the time with all of the details...I'm going over tomorrow, so we'll see what they think.

Cheers and thanks again

yeah, I went super beefy because it was a straight line most of the way.

You can never put too many deadman. Too much preen or over drainage IMO. Once it's in, it's in. Enjolras's example is almost exactly what we did with my In-laws retaining wall with railroad ties a few summers ago. Sounds good to me :)

btw, We backfilled more with rock as we went up. Hydrostatic pressure is a killer on these walls.

oubronco
06-24-2011, 05:38 AM
I prefer K-blocks with pins. 95 lbs. a piece. Much safer and easier to put in once you get the bottom level. But to each their own. THIS WAY YOU WON'T NEED DEADMEN.

Don't forget to put landscaping preen between the dirt and rocks and wrap any pipes for drainage with it so it won't get gummed up later. You can't over do the drainage. Hydrostatic pressure will doom you.

I put in a 5 foot wall 150 foot long a couple years ago. At the end I curved it into a half circle for the kids sandpit. I've been happy with the textured blocks. No splinters, no toxic chemicals. it wont fade or rot.

A whole lot of work but worth it. good luck.

Post some pics please

TailgateNut
06-24-2011, 06:46 AM
In lieu of deadmen, look into a product called Miragrid. http://www.tencate.com/2758/TenCate/Geosynthetics/Region-North-America/en/en-Geosynthetics---Geotextiles/TenCate-Mirafi-Products/Geogrids/TenCate-Miragrid-XT

TheReverend
06-24-2011, 07:37 AM
In lieu of deadmen, look into a product called Miragrid. http://www.tencate.com/2758/TenCate/Geosynthetics/Region-North-America/en/en-Geosynthetics---Geotextiles/TenCate-Mirafi-Products/Geogrids/TenCate-Miragrid-XT

^

Boobs McGee
06-24-2011, 07:47 AM
Interesting...I'm about to run out the door, but I'll definitely come back and do some more research on it later. Have either of you used the miragrid? At a quick glance, I didn't see how it was secured to the hillside.

Boobs McGee
06-24-2011, 01:14 PM
OK. So, I had completely misinterpreted the design from their original description. No deadmen will be needed (the wall itself isn't going higher than about 2.5 ft), and there's already two courses of timbers in place. The "hill" is mostly landscape rock, with a VERY minimal slope...and we'll be tying in some locking block on one edge.

SO. Big thank you to everyone for the suggestions, once the project gets started (a month or so away), I'll take pics.

thanks again.

Bronco Yoda
06-24-2011, 02:31 PM
Post some pics please

I'll try and find some pictures. Here's the products.

http://www.keystonewalls.com/pages/products/Compac.html?tab=4#Structural_tabs

http://www.paversearch.com/images/clip_image012_0001.jpg http://www.paversearch.com/images/clip_image010_0003.jpg http://www.paversearch.com/images/clip_image014_0000.jpg http://www.paversearch.com/images/clip_image006_0010.jpg http://www.paversearch.com/images/clip_image004_0041.jpg

Dagmar
06-24-2011, 07:16 PM
Posting so I can find this thread in a wee while.