Need Residential Retaining Wall Ideas 2

[xjken]

Hello. My property currently has a failing wood-tie multi-tier retaining wall on a slope that needs replacing ASAP. I did much searching and research and have come across many ideas but am looking for guidance on which to go with. COST is a BIG concern, however I want to replace this wall and not have to worry about it ever again...or at least 30 yrs.

Please give me some thoughts...
Current wall to replace is about 1200sqft face total. Three walls each roughly 4 feet high by 100 feet long. They vary in distance from eachother and towards one end, they begin to get closer to eachother then finally curve into eachother and finish off the last 25 feet as one high wall holding back the corner of my side/back yard.

New Ideas were:
1. pumping in concrete to make a single concrete wall about 10 ft high a few feet down the slope from the existing walls, then filling in and grading the property down to this new wall height.

2. three (or two) new tiered modular block walls with geogrid, such as Keystone, Anchor, Unilock or similar.

3. These "Green Walls" "Vegetated Walls" or "GeoWeb" such as the stacked bags or the block that has a large batter that is filled with dirt and plant seeds. This would either be tiered as well or just make one large slope.

I would probably need a fence for the slope idea, or a wall over 5 feet high, so that would need to be factored in to the cost. I did searches and am coming across prices from $20 to $60/sqft.

If someone recommends the Green Wall or Slope idea... I can't seem to find this product in my area?? (I'm in the New York Metro area).
Any help would be greatly appreciated! I am on a budget of about $40k MAX and am hoping for it to be much less than that. Thanks.

Ken

 

[xjken]

Yes, this is on a hill.
Thanks for all the responses on this topic. I can't find an engineer in my area! I found one person but he is an over-designer and said he will only consider a reinforced concrete wall that would cost $150k to build... I don't consider someone like this an engineer. Anyone can design a wall that won't fail. An engineer can design a wall that will work yet be cost effective and sensible.

 

[PEinc]

I stand corrected (sorta). In my last response, I should have said that whether you are holding up a hill or a flat area is not the only determination for the need of geogrids. I believe that my second sentence clearly explained my point. The presence of a sloped surface behind a wall, in itself, is not always a requirement for geogrids. For example, a very low wall with a slope behind the wall may not need geogrids. Therefore, all of the factors that I mentioned above are important considerations in determining the need for and design of geogrids.

Two other comments:
1. "But when you "cut" into an existing hill and try to use a tiered retaining wall to hold up this cut slope, geotextile/geogrid is almost always required." So is temporary sheeting. Then, you are building two walls - one temporary and one permanent = expensive.
2. "In order to avoid additional excavation for the geogrid, very often soil nails are used for reinforcement." When this happens, you have not built an MSE wall. You have built a soil nail wall with an additional segmental block facade.

http://www.PeirceEngineering.com

 

[cvg]

another option which might be considered is gabions. Especially if storm runoff or groundwater is an issue.

http://www.maccaferri-northamerica.com/retaining_wall_usa.aspx

 

[PEinc]

Good idea also, cvg.

http://www.PeirceEngineering.com

 

[BigH]

Dare I suggest using tires infilled? Might be able to get them cheap. Used in some countries I've worked in. (Naw - probably wouldn't fly in NA) Gabions work - but for 12 ft will need a couple at the bottom - could use the MSE gabion faced walls.

 

[civilman72]

Since this is a cut into an existing hill, installing a "small" block retaining wall is not desirable. For all the reasons mentioned above, this is more than likely not your most cost-effective alternative.

Gabions are a possibility and desirable if you have access issues. However, while my past experience with gabion failures could be based on poor construction, I have seen a lot of these walls fall apart over time (bigger rocks tear through facing or smaller rocks get pushed out, creating voids, and settling occurs). Gabions walls don't necessarily "fail," but can be aesthetically unpleasing.

The use for "Redi-Rock" blocks was mentioned above as a possible replacement for the timber wall. But rather than tiering these walls, have you thought about the possibility of installing one 6'-8' high Redi-Rock wall in front of the first (existing) wall and backfilling behind this wall at a 3:1 or 4:1 slope? The height of RR wall and slope behind the wall will be based on existing wall batter. Plan on removing the existing wood timber wall before backfilling. The cost-effectiveness of this alternative will be greatly dependent on the cost to haul backfill material to your site. Another positive consideration is that (I believe) Redi-Rock will provide you with a certified ret. wall design (incl. global stability), so you can avoid using your local structural "engineer."

 

[brandoncdg]

Over here in LA you can build a 4' high wall from bottom of footing to top of wall without a permit. But the dirt behind the wall must be flat. I am attaching a PDF of a slough wall so you can see what I mean.

A lot of problem projects I have seen have someone who decided to build a retaining wall that holds up a side of the mountain and house at the top, but the footings aren't deep enough to make this wall do anything and no one ever desgined the wall before building. I would also suggest using someone familiar with the codes in your area to design a cost effective wall.

You should post a picture or sketch of the yard.

Civil Development Group, LLC
Los Angeles Civil Engineering specializing in Hillside Grading

http://www.civildevelopmentgroup.com

http://www.civildevelopmentgroup.com/blog

 

[brandoncdg]

Also attaching a PDF file showing slope setbacks used out here.

Civil Development Group, LLC
Los Angeles Civil Engineering specializing in Hillside Grading

http://www.civildevelopmentgroup.com

http://www.civildevelopmentgroup.com/blog

 

[beej67]

If you're going to go with the redi-rock idea, then the thing to do in my opinion is what civilman mentions. Do one wall and backfill at 3:1 (or whatever local code dicatates) to tie to existing top of slope.

If you're hard up for fill dirt, pull all the walls out, grade flatter, like 4:1 or so up the hill a bit, then put your taller redi-rock wall in, then go 3:1 to the top of slope. That way you get some cut down that the bottom that you can use for fill at the top. Design your wall height, wall location, cut slope, and fill slope around what makes your cut and fill quantities work, so you don't have to bring in or haul off dirt.

In fact, that cut/fill analysis would be a fun exercise in basic civil engineering for you to toy with, xjken. Google the terms "shrink" and "swell" first. That should be fun stuff to get you started.

Good luck!


Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[19861023]

You can use the geogrids, Before placing geogrids, excavate to the lines and grades shown on the project grading plans and clear the ground surface of all debris or as directed by the
design engineer.what's more the cost of it is very litter, if you make a right products.
And i don't agree with some persons, because the geogrids is not very expensive even if you need the tanser's quality.



gengnan1@gmail.com

 

[xjken]

OK all. You have provided much useful info and help. After all this info and reading into this more, I think I came up with a final idea that I am going to submit for permits and construction. I am going to do a 6' segmental block wall with geogrid, gravel, drainage, etc approximately 4ft down from the lowest wall. There will then be a slight slope, maybe 1:5 from that wall to about 15' out where I will then do a second wall of about 3' high using segmental block and no geogrid.

I attached a pic of the existing conditions as someone suggested above.

 

[RHTPE]

Just goes to show how "permanent" a landscape timber wall really is. I have one in my yard - the carpenter ants have now overcome whatever cheap pressure treating was used in the timbers.

Retaining walls need to be made of an inert, inorganic material to last. They get especially difficult to rebuild when those little trees that were planted when it was built have now grown to substantial size.


Ralph
Structures Consulting
Northeast USA

 

[Boondog]

I have designed and installed litarally millions of square feet of virtually all of the walls described above. Here are some thoughts:

Redi-Rock: big and pretty but expensive to install. 12 feet tall will work without grid with the 60" base IF everything is level on top and bottom. A "bobcat" will have trouble moving these. Installed cost $35-$40 per square feet. They are very proud of their blocks.

Modular block: quick and easy. Design build contractors will handle the design and permits. Installed around $14-$18 per square feet.

Welded wire form slopes: Cheapest. A vegetated slope at 0.33:1 vertical batter will be ideal for your situation and again, a design build contractor will handle this for around $12-16$ installed.

Keep in mind these are for the facing, reinforcement and backfill placement. It will not include the backfill material or demo/excavation. Please don't even use the L word (landscape architect)when it comes to structural retaining walls. I have rebuilt dozens of walls "designed" by landscapers. I would shy away from the reclaimed concrete blocks due to the cold joints and inconsistent construction.