Rubble Retaining Wall design standards?

[Dinosaur]

I have access to left over 4x8 concrete cylinders. I have a nine foot high berm behind my house that serves as a poor noise barrier between me and the highway. I would like to terace the berm into three three foot high sections. It seems it should be possible to stack 4x8 concrete cylinders to create a rubble retaining wall.

I have started some rudimentary calculations to get a handle on the project. I have checked sliding with a F-of-S of 1.33 and also overturning. I am using Ka to determine the governing soil pressures. What sort of things are done for making retaining walls from rubble?

There is one section where I may want to combine two walls along a 20 foot length so I would need a 6 foot high section there. This will absolutely require some kind of tie back or deadman if I can get it to work at all.

Before anyone says "Why not use those blocks they sell at the home improvement store?" The answer is, the blocks would cost $15,000 and I would still need some gravel for backfill, etc. I can build the three foot high sections of my project by myself, although it may take several years to complete the project as a "weekend warrior". Right now, I am just stockpiling the cylinders for next years part of the project and doing some calcs to make sure it doesn't all collapse.

Any help would be appreciated. Thanks.

 

[cvg]

you could get some wire mesh and make your own gabions using the cylinders instead of rock fill. since gabions typically come in 3' x 3' baskets, it would be easy to create your terraces

 

[Dinosaur]

Gabions, that's a good idea. What proportions should I make the baskets? Chicken wire OK, you think?

 

[oldestguy]

Over the years it has been found that for a gravity retaining wall, which I think you would call yours, with a horizontal top surface of earth, the following works fine. I have done this many a time, no calculations, using rocks, no binder materials, wall heights up to 6 feet.

The base width (front to back) of the stone, blocks, etc, in one unit, stacked together by somewhat of a interwoven patterened bonding, should be no less than 1/3 of the height.

You can cheat a little, by narrowing up the upper sections to give a sloping front face and mayebe some slope in the back, but not drastic cheating..

For your terracing plan, then a fussy person would run some slip circle type calculations, using the angle of fricton, cohesion and unit weights. However, the US Navy Design Manual NAVFAC DM-7 has some general info that you may be able to use by assuming your terraced front slope and various steps are one unit.

With no big need to worry about a failure and loss of a building, etc., I'd just take a 60 degree slope up from front face of lower wall base and make sure that none of the upper "walls" project into that line, but are back of it. Each terrace wall meets the gravity wall dimension ratio of 1 to 3. Each unit is as dense as possible, giving it the gravity effect it needs. This is not on the basis of any calculations, but rather what I have seen people "get away with" in my some 50 plus years observing.


With those concrete test cylinders, you then know you can't just use them as a front "face" and none behind as a gravity wall. (I won't say impossible, since many a concrete testing guy has done just that and it works, due to the material behind having good cohesion, etc. In that case it is more of a device to prevent erosion of a steep earth slope that otherwise would stand by itself.)

Sloping your whole syetem units "into the hill" also makes it safer than vertical units.

 

[cvg]

for everything you ever wanted to know about gabions, check out

http://www.maccaferri.com

 

[Dinosaur]

Thanks for the dimensions. Do you think chicken wire will be OK to fab up the baskets?

I had been working out the dimensions for just stacking the blocks. According to my calcs, I could use a single thickness (8 inches) for the top three layers before sliding would be a problem. Below that, I need two thicknesses which will work until you get to a wall height of just over two feet. At this point overturning controls. All these were computed using active earth pressure, a batter into the slope of 1/2 inch per layer (e.g. each layer of blocks is set 1/2 inch behind the layer below) and no morter or any other binder between blocks. The lowest block is set into the ground and another block is set into the ground in front standing upright to get a sort of key into the existing soil. All the wall will have a 4 inch wide layer of gravel behind to insure free drainage.

There are several unsolved problems with this approach though. How to handle construction of the ends of the wall? How to get the final 8 inches of height I need cause of the overturning problem? How to make the wall more than 3 feet high in one spot? Gabions solve all these problems.

One good factor in my favor concerning global stablity is that the slope I have now is an existing slope of about 15 years age. This has permitted the soil to consolidate so settlements and other soil problems will be mitigated. The wall will induce additional pressure, but not the additional pressure of the full height. The steps are set back about 5 feet so they will be in the existing soil at their base and help prevent failure by intersecting curves.

This is becoming more satisfactory because I wanted to make sure I could sell this house when my son is educated, and walk away without worring about getting a phone call that the wall collapsed. My fear was that the new owner would think I had placed too many cylinders in the wall and then try and remove a few for another purpose. The gabion baskets prevent him from doing anything stupid.

 

[cvg]

gabion wire is typically much thicker than chicken wire, however, even one thickness of chicken wire would provide some additional strength and stability over just plain stacked cylinders. two layers would be better - or use a heavier welded wire fabric

 

[SlideRuleEra]

Plans to build gabion baskets per California DOT

http://www.dot.ca.gov/hq/esc/oe/pro..._US-customary-units_06/viewable_pdf/d100a.pdf

and

http://www.dot.ca.gov/hq/esc/oe/pro..._US-customary-units_06/viewable_pdf/d100b.pdf

"Gabion Walls Design"

http://www.gabions.net/downloads/Documents/MGS_Design_Guide.pdf

http://www.SlideRuleEra.net

 

[Panars]

My father built a low retaining wall out of 6x12-inch concrete test cylinders at our house when I was growing up. He was a project engineer at a bridge job at the time. The wall was only about two feet high, but the front face was battered back by setting the next row of cylinders about one inch back. The wall had good drainage out of the holes between the cylinders.

I would think you could use the same priniciples of analysis as used for the modular block walls. The differences would be in the friction between the rows of blocks. Since you have the blocks, you could perform some tests to determine the friction angle between cylinders. For higher walls that require a geotextile reinforcement, you would have to figure a way to connect the reinforcement to the concrete.

 

[Dinosaur]

I did a friction test and came up with 36 degrees at sliding. Tan (36) = 0.727 I am using 0.5 for my coefficient of friction.

I am doing the same thing as your dad except I am using 4x8 cylinders and I want the walls to be three feet high each.

My biggest concern now is how am I going to get the excavation done to get the first layer started. I also have to store a large amount of coarse aggregate before I begin the excavation since I want 4 inches of stone in the bottom of the trench. It also has to be dead level.