retaining wall

I'm shooting this off knee jerk so bear with.

I am ass u me ing that you will cut the 6x6 logs and set them as posts (vertical). Or are setting vertical rebar and using the 6 by's as horizontal bracing. If you are retaining material that could compromise property and or safety of people consult someone in the know.

While working on the uncle's garage we decided to build a retaining wall of 4 x 4" posts using 2 x 6" planks. The soil was just a bunch of hard rocky junk, hardly soil at all. Just hard crap. The embankment was only about 45 deg, with a little 30 deg step atop. It had been there since the house was built. We dug, set and sledged the first piling and down it came. No one hurt. No real damage. The real problem was now dealing with the hillside that was now stacked 4' vertical against an unaccessible rear wall of a garage.

Just my experience. You might not have need of that info, but I would be remiss not to convey.

Happy pounding. Hopefully you don't have the heat we do right now. Or you do have the labor provided.

cr3

Not my field of expertise...

I just want to know what do you mean by 65degrees...is that measured from horizontal or vertical?

I read CR3s story...a timely warning indeed...I'd always be inclined (joke) to set my post off vertical by say 10 degrees, leaning back towards the soil of course! I'd personally go for something more permanent than timber if it's more than say 1metre high.

How high is the wall, how high/how far back does the slope continue? e.g is this a mountainside or just a raised section of garden?

More detail may elicit more informed replies ...

A wooden retaing wall is not a very good choice, unless it is temporary. A 65 degree slope is almost vertical and again not a good choice to put a wall on. The top should be fairly flat and the bottom needs to be fairly flat. Without getting a geotechnical engineer involved you are messing up bad if this wall is going to be over 3 to 4 feet or 1 meter tall. However, attached is a link to a scketch that will show how to build one out of timbers.

http://www.bhg.com/bhg/story.jsp;jsessionid=EPZVLJMSPUIZFQFIBQSB42Q?catref=cat820070&page=2&storyid=/templatedata/bhg/story/data/12418.xml

I visted the website, building a retaining wall with logs lying horizontal is beyond me, A post, is set vertical, which is what I have done, dug a hole approx 18-20 in. deep and 4 feet apart, hight for is row is planned at 2-2.5 ft.

18 - 20" deep !!!!!

That is no where near enough.

I wouldn't put up a garden fence with holes that deep and expect it to stand.

I would seriously recomend a re-think.

If you actually want advice then provide as much info' as possible.

why 18-20 in. deep is not enough, the base of the hole is approx. the same, poured concrete to secure them.

24" is a standard post depth for a quality yard fence where I live -- could be different where you are. There are fencing contractors here who will do less in the name of laziness.

It doesent matter if the base is 36 - 72" dia and filled with concrete. The idea is that if the precarious above wall load should come down, then the surface area of the wall is going to provide a lever to your shallow poured fulcrum. You did say 65 deg. Even if you are off by 15 deg, and me not knowing how much run is allowed, you could be making things worse down the (now covered) road.

Depth not diameter. And with digging to depth be mindful of unsettling the soil. Again you might just be trying to keep a bit of loam off the petunias; in which case I wonder why you are not on the Better Homes and Garden website.

If this is even remotely a structural matter I refer you to my previous post, while reserving the right to say " I told you so" at a later date.

cr3

The fulcrum changes when concrete is added to the hole, not to mention added weight at the bottom. Maybe this is is in error but i have seen many fences blow down that were just set in earth alone - in inclement weather the earth becomes less stable and the larger the base hole with concrete adds some stability.

Don't mean to be argumentative but it is tried and proven for decades -- even without engineering analysis. The more stable the bottom the more secure the top.

You are not being argumentative, I don't think. You might need to trust me on this one though.

Take a steep (45 + deg) incline. Dig a series of shallow holes, any diameter you wish (within reason). Set vertical posts and fill holes with concrete. Build 2-4' high wall, x feet in length using previous posts as vert support. Now dump about 2000 (conservative?) lbs of dirt at 10 - 15 mph on said wall with shallow concrete footings (mind that the ground is now unstable. see minor landslide?). Record results.

Can I watch? Please. I wont stick my tongue out. Ok I would probably stick my tongue out.

cr3

Yes you are correct - any structure, no matter how well planned, can be forced to fail under extreme loads. The method described by the questioner is inadequate in my mind and I was only trying to suggest some safety factors.

If my grandchildren were in this persons yard I would not let them near the structure he described.

I am only pointing out that reasonable planning for any given situation is a good thing and should be taken to the point where failure is minimized to the extreme.

Consult a civil engineer. 65 degrees is a seriously steep slope. However, most jurisdiction don't require any engineering unless the retaining wall is a structural support, usually over 4 to 5 feet high for most residential applications. If this is meant to actually retain a soil load, you need to consider how much soil lies in front of the foundations for the support columns to resist movement. You may need to deepen the foundations to resist movement forward at the top. Alternately you can always tie the column loads back into the soil behind the wall, which ever is easier.

Is your post in response to me, ietech, or the original poster saca03142? --

I, ietech, am in total agreement with you. See post 9, 10, 12, 14, 15, 24.

I'm with the cat guy --- 18" - 20" is a far cry from adequate even for a yard fence on level ground not bearing any load but the wind forces against in in bad weather.

Just for a simple fence I sink my 4"x4"x8' posts 24" deep in an 18"+ diameter hole and backfill to the top with concrete.

Since yours will not be just standing but supporting a load I would not go less than 24" deep with a reverse angle (as previously posted) For a 6x6 post I would make my post holes 24" diameter holes backfilled with sufficient concrete.

Just my way of doing it -- I could be wrong - but wrong in the direction of safety.

DO NOT KNOW WHERE YOU LIVE AT BUT, MY FENCE WITHSTANDS WINDS ON A DAILY BASIS OF 25 MPH, USING 4 X 4 WITH METAL BASED AND HOLES DUG 18 IN DEEP, MY CHILDREN AND OTHERS PLAY EVERYDAY IN THE BACK YARD. i WISH i COULD PASTE A DRAWING OF MY PROPERTY SO YOU COULD HAVE A BETTER IDEA, BUT MY QUESTIONS FOR IS WHY DO YOU THINK A 6 X 6 AND 18-20 INCHES DEEP IS NOT STRONG ENOUGH?

Jeez.. you asked a Q.. Every single one of us thinks it isn't strong enough!
Should we really have to explain why?

With CR3's post it is experience.

With me it's engineering feel, common sense and the fact that I've seen fences blow down.

If you want to get buried in a land slide fine..!

If you want to see calculation maybe you should hire a civil engineer. (We've tried to be civil but it hasn't worked )

Don't ask my opinion and then expect me to justify it... Mrs Cat does that quite adequately without your assistance!

Dude. Easy on the caps. That stuff is hard to read.

I am simply saying that by sheer DEFINITION IT"S A RETAINING WALL. Notice that a fence is different from a retaining wall. When he asks about how to build a fence I will offer up a tale of my fence building experience.

Usually I like to insert links with definitions so one can quickly ascertain such differences. But I am upset about all those capital letters. So...

It is because or the 65 deg angle you describe the rise that will be behind the retaining wall -- 65deg is darn near a cliff -- not sure how long the run upwards is though.

If you are just trying to build a decorative wall or a wall to stop small rocks or dirt from coming off of the slope your idea will probably be fine. If you are trying to ensure that the slope will not move into your space -- then I would consult a professional.

A wood retaining wall will just become part of the debris if the slope decides to move.

If I were trying to retain this rise I would trench and put a concrete footing and reinforced concrete wall high enough and deep enough to retain the slope if it decides it wants to level itself.

I would listen to the advice of Rummel.

I had a home on the west coast with a retaining wall in the back yard. It was engineered and still managed to slip into the ravine. If its structural, seek professional advice.

Soil is unpredictable.

there are way too many unknowns here to make any kind of suggestions.

how high an embankment are you trying to hold back?

what type of soil will be behind the retaining wall?

those at least for a start.

bear in mind that average weights for soil can range 100 to 150 lbs per cubic foot. (Sorry Del, we're never going to be able to go metric over here until all the contractors do)

also bear in mind that you are not trying to hold a lateral load... your footings sound weak even for that. You are really trying to resist an overturning moment and your footing is the fulcrum that will be the point of rotation. The load that you are trying to resist will be represented by a triangle whose legs extend as far back over the retention equal to the height of the retaining wall. if your retaining wall is two feet high, then each foot of your retaining wall will need to resist an overturning moment of 300 pounds...

keep us posted.

PROPERTY IS APPROX. 60 FT. WIDTH, and 70 deep, have a back yard approx. 30-35 ft. deep distributed as follows: two semi round planters at each end of property approx. 12-15 ft. width made with a retaining wall approx. 5 ft. high( one foot foundation for blockwall, the retaining wall has a supporting floor approx. 15 inches high, concrete floor from the retaining wall to the slope is approx. a 7 ft. walkway being created with the additional retaining wall. My goal is to build a series of tiers( 4-6) for maxinum use of terrain and do gardening, I have planted a few trees for erosion control.

Architect, this is the kind of response or questions I wanted to hear, a "just won't work or is going to fall" in my opinion is not correct, given the property description thought it would get me more reasoned responses. I live in southern California, hardly ever rains, is sandy soil, I have lived in the property over 12 years; Initially it had a 3 ft. high retaining wall 18 ft. away from living quarters, and it was falling. I have two large trees inside the planters, well rooted, planted three more up the slope, tore the retaining wall down and removed approx. 40 cubic yards of soil and increased the backyard by another 16 feet (approx.), the 40 cubic yards were replaced by a concrete slab, framed and 4 " thick and two 8 inch steps at the end, built a block wall approx. 20 ft. wide and the two planters, one on each side. There is no cliff or ravine and I have done handy work for years. My question, originally, was hoping for someone to come up with a formula or reasonable way to finish the retaining wall, if 4 ft. span was not enough I could reinforce it with one more post, a red wood 6 x6 is very strong, I just do not know the pressure or load teh posts will sustain.

I know everyone's intentions are good and the advises are well taken, it just happens that I live a zone that is not prone to flooding, so I really do not know how can the slope give way. Is so dry that I decided to plant cactus on top of it, but I want to change it and do gardening.

Please disregard any of my previous posts/suggestions. After looking at the responses made by others you need a pro to deal with this issue.

A 65deg slope is VERY steep and I don't think anything suggested here will contain that hill if it decides it wants to move. Maybe -I hope - it is only a 25deg slope then the type of solution you propose might work.

See C_Rummel3 post #1 and place value on his experience.

Two feet

Four legs and a trunk.....?

is it an elephant? it's an elephant! I know it is. I like elephants did I win? I won. I know I did. is it coffee? I like coffee! what did I win? please tell me.

What? two feet. four legs. a trunk. ? An ashtray? A freakin ashtray. I'm going home.

Am very late on this thread, but my suggestion is that there are many hydraulic hammers these days that are available . These are not only fitted to crawler excavators but as well to : wheel back-hoe/front shovel. Talk to an operator who has good experience , he will surely advise you, though not all have used these rock hammers as small pile-driving hammers.

For total peace of mind let me suggest the following:

1.Hire one and have the operator drive 2 or 3 inch diameter lenghts of galvanised pipe into the ground (at least two per anticipated concrete or wooden panels that you intend having as retaining walls.) The depth to which you should drive should be not less than the height of your retaining wall ( Except of course if the driving shows that the pipe/pile being driven , has reached a point of fixity (i.e.when the pile does not move further within a minute of it being hydraulically hammered into the soil)

2. If the soil is very unstable drive anchors at least ten to fifteen feet from the retaining wall line. You can then prior to backfilling use galvanised wire attached to the top of the wall piles and back to these anchors. I suggest that you use adequately sized turnbuckles. These handy gadgets (see harware store) are to be used to tension these stays before doing any backfilling. ( A welder friend of yours can weld on the first row of piles a piece of flat steel with a hole cut out so that the retaining wires can be threaded through and be invisible i.e buried in the fill ). That is if you want the job to be esthetically attractive and professional.

In the event you are unable to find a rock-hammer operator to help you, a simpler but less certain and safe way is for you to use a manual pile driver to drive "star-pickets" (these are steel "star shaped " steel fencing posts usuall six to eigh feet long). Many fencing contractors use this simple system . Again a lenght of 2 to 3 inch pipe is needed usually about 48 inches. The top of the pipe is welded with a flat steel plate. Two handles made of 3/4 to 1 " pipe are welded onto the main pipe. Both lenghts are about 3 feet long.they are paralel to the 3 " pipe. By placing this "rammer" onto a star picket and lifting and lowering sharply you will have a manual pile hammer. This tool could serve you as the means of anchoring a back wall which if properly executed would serve as the front retaining wall anchor. The wall could be in concrete wherein the above star pickets would be embedded.It should be at least ten to fifteen feet away. Again wire stays would be anchored to that secondary wall and would hold the top of your retaining wall. This would ensure that it acts as a permanent barrier for the front wall . It would restrain any overturning moment about which you have soundly and well been warned by the other subscribers.

Be carefull both systems are best executed by people who have experience and who understand and apply good engineering practices. If you are unsure : DO NOT ATTEMPT TO DO IT, more so if you have earthquakes in your home state.Particulalrly if you want to have your kids and grand-kids play around the wall you have built.

Though all of us may joke about this deal seriously take the above and earlier precautions freely given to you ( I happen to be a Civil Engineer).

Labor

Thank you very much, very informative. I will proceed as suggested.

Do you have construction permit from City. If not get it first, otherwise you will be left chewing lemon.