Who knows about stacked-block retaining walls?

[lilranch2001]

Muhammad is somewhat of an expert in wall building himself…..
Maybe ask him for his advice.

 

[CurlyDave]

"The bottom row can’t kick out because there will be a paver-floor against the house holding it."

What that really means is that if the bottom row has enough pressure behind it, it will push on the paver-floor which will in turn push on the house. The pavers are too light to develop very much friction against the ground.

YOU REALLY DO NOT WANT TO DO THIS. You especially do not want to do it if there is a basement under the house. The top of a basement wall is the weakest part.

I am an engineer and have built many retaining walls.

In my part of the country we would put "3/4 inch crushed clean" rock behind the wall.

The reason water is devastating to a retaining wall is that the soil is treated as a liquid with a density of 40 pounds/cubic foot when designing the wall. (Obviously the soil has greater density than this, but it is semi-solid, and 40 pounds/cubic foot is a good approximation of the forces it produces.) If water is not drained from behind the wall it adds another 62.4 pounds/cubic foot. If the water freezes the forces become very large.

 

[thclimer]

I'm sorry that I don't have anything to add on building your wall however, I'd also be a little concerned about the 2 trees that seem to be with in fill that is requiring the wall.

Trees typically trees don't like to have their trunks buried, has the fill around their base always been there?

 

[CoyPatton]

View attachment 2478550
They tip back one inch for every 6” up.

Thanks very much for all the suggestions and wisdom.

As you can see I’m building this from old blocks, and not solely because they’re cheaper. They’re almost “not” cheaper because of the physical labor to get them. But I didn’t have to pay 10% tax either. Including other reasons for it to look like it was done “long ago”.

It would have been wise to sandwich some geotextile flaps between the layers, leave them hanging out there for the retaining wall but that’s a first-timer for ya.

For tiebacks I was thinking of driving rebar rods and then figger a way to attach to the blocks.

I don’t have space for a drain pipe at the bottom. Have to put it at the 3rd course. There could be water here if my driveway drains “go unmaintained”. I think everyone knows that driveway drains eventually ALL “go unmaintained.”

The bottom row can’t kick out because there will be a paver-floor against the house holding it. And if what I read about geotextile soil retention is true- the bank won’t push. What do you guys think about that? Have any of you observed geotextile lifts behavior (or failure) over “years”?

If you don’t have space for your drainage pipe at the bottom, you din’t have room to build a lasting wall! All you will build is a mess that will fall—sooner than later.
Rebar is a poor choice for what I always called a deadman. This “deadman” needs to interlock with the wall, extend several feet into the hillside then have a T-bar interlocked with the extension. These should have compacted soil all around it for at least 1’ on all sides.
Water is it biggest enemy on a retaining wall.
Lots of good advice in comments which you seem to want to disregard.
In my opinion an I have build about 100 retaining walls over the years (unfortunately, I did not have the internet to advise me in early years and I had a few walls fail some very quickly), if you plan to do what you described, plan to rebuild within a couple of years—rebar for wall stability is useless, rebar bends easily and by itself is too small to havre any resistance, it is made to add to concrete. 3 courses of blocks prior to drainage pipe means 18” of wall at its most critical location, holding water—approximately 8.5 lbs per gallon, then you have the freeze factor your area has freezing temps. Experience (personal and from others here) says don’t implement your plan.
Sorry to be do negative, but you have already put in a lot of work, do you want to redo part of what looks like a good start on the hillside?

 

[vagem55]

Airbiscuit showed the proper use of geotextile fabric, between the blocks, level into the fill area, to hold the wall back (useless if not attached). Not clear what your fabric would actually accomplish. My 1600 blocks are 90+ pounds each, filled in and behind with 57 stone gravel, with fiberglass pins securing the blocks together (yours have a lip on the back). Blocks with the rear lip aren't designed for high walls (some say two feet max), and I'm curious if placing geotextile fabric under the lip defeats its purpose. As LD1 stated, 57 stone is used in and behind those blocks, and you need a drainpipe at the bottom. However, my instructions stated compacted 21A stone footer 12" below the wall, which keeps the footer from retaining moisture. My four-foot and above walls required 12" below grade.

 

[GeneSimm7]

Make sure you put in deadman tiebacks and backfill with something that will drain well, Not sand. 3B gravel would be good, 2B is also OK.

 

[fishdoggy]

I see water issues from the start, the drain from a gutter and one from the washer discharge probably. I have little experience in the wall, my railroad tie retaining wall was 3 feet high and replaced after 25 years, is tilting over now after only 10 years. But I will say put some treated stringers from the bottom of stairs out to end of house, deck boards over them will allow you some room for drain tile and stone under the wooden walkway, I see water problems down to edge of house regardless of your retaining wall.

 

[aircommuter]

As a general engineering contractor I think you need to follow the manufacturer’s installation procedures. Which is like the drawing included by airbiscuit. First thing I see is the black pipe connecting to a pipe that goes behind your wall. Where does the black pipe come from? Is it all solid liquid tight or? Like others said you can’t depend upon pavers and the house to become a structural item. To answer the backfill question again 3/4 drain rock. Impervious plug at the top is a must as you don’t want to introduce surface water to a subsurface drainage system. One thing about this discussion that I hear a lot is the use of the term geo-fabric. Before you start using the fabric you need to study the different types and use the appropriate type in the location/s as needed. Every type has a purpose. You also should protect the area between the proposed wall and the house from any water from other areas (like downspouts) and make it drain away from the house and the wall. Seems like you may need to backup a bit in this project.

 

[EddieWalker]

After thinking about this a little more and remembering some of my issues with trees over the years, I think that for this to work, you need to remove the trees. It's probably the hardest thing to do, but there is no such thing as a good tree next to a house.

If the trees are gone, the retaining wall becomes an easy project. If the trees are gone, the house isn't in danger of falling branches, or even worse, the tree falling over. Nothing from the tree will fall on the house. Mostly they are cosmetic. Some people think they add shade to keep the house cool, but it's not enough to be measurable.

Overall, trees close to a house are a bad idea no matter where the house is. Trying to build a retaining wall between a tree and a house, with the tree being on the upper side of the wall is asking for trouble. Maybe not right away, but it's a good bet that somewhere in your future, you will wish you had removed the trees.

On my land, I've removed trees that I really liked. I tried talking myself out of removing them because they were such nice trees. But looking back, I'm really struggling to remember them, and now that they are gone, I don't miss them like I thought I would. In the last 20 years of having my land, I wish I had taken out more trees. But where I live, trees are like weeds, and we have too many of them.

 

[vagem55]

It seems like you're using the fabric to keep the dirt back. I believe it's intended to hold the wall in place, with the backfill being securely compacted in layers. That said, I don't think those blocks are designed for a wall tall enough to require geotextile fabric.