Retaining walls-suggestions???

[wroughtn_harv]

As everyone said, "deeper trench."

A couple of thoughts.

One, deadmen. They're easy to do. You take a telephone pole and put it six to ten feet above the retaining wall. You lay it in a trench so it's parallel to the wall. You tie the wall and the deadman together will large all thread. The reason I suggest all thread is you have the potential for later adjustment if required.

Two, I'd tie the poles together side to side. What I've done is to drill a three quarter inch hole through two poles at a time. I then drive either rebar or three quarter inch hot rolled steel rods into the hole.

You place your first two poles in the trench and then tie them together as I've suggested both high and low. Then you place the next pole in the trench and tie it to the second pole the same way but out of line with the first set. You add each additional pole the same way.

This is much easier than trying to drill all the poles so you can tie them together with one continuous rod.

I would definately find out what the local practices are for filling in behind retaining walls. I've built them and always put in drains through the wall and a french style drain parallel to the wall when possible.

If you don't put forty two inch high rails above the retaining wall then you're being very foolish. It isn't just the liability of someone getting hurt you have to worry about. It could be someone you really care about who is the injured person.

 

[kyoders]

I would also recommend hiring an engineer. You should also check into your local building code. Around here, anything over 2' tall has to be "engineered" and permit'ed. A retaining wall 6' tall is going to have some incredible stresses on it, and in the long run, it will pay to have it designed appropriately. Everybody else's suggestions are good ones, it's just a question of how often you need a deadman, and exactly what type of foundation you need, etc.

You might also want to re-consider the telephone poles. It sure sounds good and cheap now, but labor is going to be your biggest cost in doing this. I don't know how long telephone poles should last, but around here, wood is generally frowned upon for structural walls (as opposed to decorative only). Not just because they eventually rot, but freeze/thaw cycling on wood can be devastating to it.

Kevin

 

[micromike]

I've also wondered if you are committed to telephone poles. I'm not an expert but I believe there are better materials for retaining walls.

A couple weeks ago, I was driving through Parsons WV and saw a recent retaining wall built by the city. It must be 50 or 60 feet tall and 120 or 130 feet long. It is made of solid decorative concrete blocks that are designed for retaining walls. I was very surprised, had no idea they could be stable this high. They are wedge shaped on the sides so you can make convex or concave curves and each is set back about 1/4 to 1/2 inch from the one below it. They are simply stacked. I don't know if there is a dead man built into it, and not sure how this could be done. I believe the idea is the wall can move slightly without buckling like mortored block.

Since I've been looking for them, I noticed another project in another town where three sides are built up over 20 feet and filled. There is a gravel parking lot built on top of it.

Sooo....I checked out the cost of the blocks. Over $6.00 a piece at Lowes. Ouch! The thing is I think I can build some simple plywood forms and make my own blocks for a buck or two a piece. I'm even considering stain to make them look more like cut stone. I think it could be a good winter project. Wouldn't take long mix up a batch and shovel it into a dozen forms. Couple dozen every weekend till spring would do me fine!

Anyone have any experience with these types of walls? Do they use a dead man system? Any thoughs appreciated.

Mike

 

[mrcaptainbob]

PT phone poles were used for 'mini' retaining walls at the marina. The parking area is probably 5' higher than the seawall. (Some are over 6 1/2'.) The retainers are about 100' long and as much as 5' high at the center gradually down to 3' at each end. There are at least 6 of these walls. That forms a nice walk way along the seawall of at least 6' wide. There is evidence of threaded rod through a bearing plate on some of the poles, (as WHarv suggested). The parking surface is always a minimum of 6' from the ends of the 100' span. They're holding up very well, considering the extremes of Michigan winters. No evidence of movement from any of them in almost ten years from install.

 

[Anonymous Poster]

John
I replaced a railroad tie wall with a product called Allan Block. It is a hollow block that interlocks and you fill them with gravel. My wall if almost 6 foot high & 70 foot long. There is a place near me that has an Allan block wall that is over 12 foot high (that is where I got the idea to use Allan Block). The product is easy to install. I installed mine on a gravel footer, installed a drain behind the wall, 18inches to 24 inches of gravel behind the wall.

It has been installed for three years and there is no sign of pushing or sagging. I keep my eye on a couple of walls that were constructed before mine and they are all in good shape.

Just another option. http://www.allanblock.com/

John

 

[Anonymous Poster]

Allan wall construction picture

John

 

[kyoders]

I can't remember the name of them right now, but one of the local supply places had a block system that consisted of structural foam blocks like the large Allen blocks, plastic tie clips, and geotextile fabric. The blocks were filled with stone, and the fabric was attached to the blocks every few courses and pulled back into the backfill area. This was effectively the "deadman" for the wall. The system was supposed to be designed for building large scale retaining walls. There may have also been a requirement to have somebody from the company inspect the site to recommend the design details, but I can't remember.

The blocks/clips were about $5 or $6 a piece. I didn't get pricing on the fabric because the wall I was looking to do was only 2' tall and wouldn't require it. I ended up going with the interlocking blocks you find at Home Depot/Lowes because I found somebody selling "used" ones real cheap.

Kevin

 

[kyoders]

Mike,

Check with the manufacturer of the blocks for installation details. I found 2 styles of blocks at Lowes. The ones you are talking about are designed for large structural retaining walls. The other style (about $1.90 each and much smaller) are more for decorative type stuff, not for holding back much hillside. I believe Castle was the manufacturer for these, and they explicitly say not to go over 6 courses (2') from grade. The larger ones could go higher, but I don't remember how high. If you are going to try to pour your own blocks, I would try to make them as close to the commercial ones as possible. I'm sure the type of concrete has some bearing on the specs (I know next to nothing about concrete), so you might want to see if the company specs out what they used to make theirs. If you match what they've done closely, you could probably use their construction guidelines for how high you can go with them.

Kevin

 

[em14]

Mike,
Retaining walls of any height above a few feet have more pressure on them that you might imagine and to answer your question about dead men … well they may not use a dead man as you might think of a dead man they use many different methods to aid in the stabilization and strength of the wall to prevent failure … check this web site and I think you will find the answers to your questions There are some very tall retaining walls and many are mortar less .. there is a lot of Engineering in the design of a retaining wall and they should not be taken lightly … improperly Engineered they can be very dangerous … yet many people get lucky .. in most places I think there may be codes covering them as well as inspections .. if you built one you must be aware of the drainage, compaction (and the kind of back fill material used), and pressures on the wall.

http://www.keystonewalls.com/

Leo

 

[yooperdave]

Hi Mike,

The blocks all interlock, and usually use a row(s) of geotextile as a tie back(s) depending on height, loads, surcharges, etc.

Using solid poured concrete blocks is ok, but realize that you still need to provide an interlock detail which will engage the geotextile as well as the adjacent blocks.

Type and placement of back fill is very important. This type of wall has numerous advantages including flexibility, durability, and not requiring a foundation which needs to extend below the frost line.

Good Luck

Dave