Who knows about stacked-block retaining walls?

[jigs_n_fixtures]

OK I'm smelling an engineer..... Thank you jigs for reading thru! And any other engineers too!

I'm quite capable of perforating a PVC pipe
....onsite,
in a fraction of the time it takes to walk the aisles at Home Despot.

What I'd like to know is,,,,, (knowing you're not able to look at the site in person...)

THIS -----> block wall leaning 1:6 into a geotextile layup (of sand),,,,,
Do I need to concern myself (at all) with tiebacks?

Depends on our seismic zone. The entire Pacific Coast has a pretty high-risk level. If I had done a design, I would have included them. I'm a belt and suspenders, with tight pants kind of guy.

At this stage, it would be difficult to do right with any of the inexpensive systems. Drive toggles might work, with your sand filled geotextile lifts. Something similar to these, which I have used to install aircraft tiedowns. I've driven them with an SDS-Max driver and a ground rod driver attachment to drive the rod:

Duckbill® Earth Anchor

 

[Sodo]

The trees are buried.
Anything that slows their growth is fine by me.
They are too big already, and too close to the house.
We have tree canopy protection laws here, If the tree wants to show distress, I need that (for the death-warrant).
I wonder how susceptible Redwoods are to trunk-rot.
Redwoods are not natural here, but these 1985ers sure like the growing conditions (in sand).

They are beautiful trees .....if they were farther from the house I would admire them greatly.

Speaking of beautiful, that's a beautiful suggestion !
I can build duckbill anchors.

Another idea...I have a gas-powered fencepost driver.
What about T-posts as tiebacks?
I can drive two T-posts, splayed out at 45° (with some effort....) and one vertical.
Weld three together where they meet.
I bet that would hold more than a whole flock of duckbills.

The biggest Q I have..... remains...
Here asked a little differently.
Does a geotextile layup exert pressure against a retaining wall??"
If it does not, tiebacks seem unnecessary.

 

[jigs_n_fixtures]

The trees are buried.
Anything that slows their growth is fine by me.
They are too big already, and too close to the house.
We have tree canopy protection laws here, If the tree wants to show distress, I need that.

They are beautiful trees .....if they were farther from the house I would admire them greatly.

Speaking of beautiful, that's a beautiful suggestion !
I can build duckbill anchors.

I have a gas-powered fencepost driver.
What about T-posts as tiebacks?
I can drive one at 45° and another vertical, and weld them together at the top.
Or two, splayed out at 45°, with one vertical.
I bet that would hold more than a whole flock of duckbills.

The biggest Q I have though, does a geotextile layup exert pressure against a retaining wall??

I'd be concerned with t-posts rusting out over time.

 

[CurlyDave]

Does a geotextile layup exert pressure against a retaining wall??

Even if it doesn't, the fill between the geotextile layup and the wall will exert exactly the same pressure on the wall as if the geotextile layup were not there.

Think of it this way, if I have a 30' vertical piece of 1/2" pipe and fill it with water, the pressure at the bottom will be exactly the same as the water pressure 30' beneath the surface of the largest lake on earth.

No matter how thin the fill layer is, the pressure vs. height relationship is the same. AND, no matter what you do, the fill will always be there. You can either choose what the fill will be by placing it there yourself, or allow it to form from whatever debris is washed out of the geotextile layup, or washed into the space behind the blocks from above. Over time a void behind the wall will always fill up. It is far better to have a material you select than whatever random collection of debris forms naturally.

 

[Redlined0002]

I'm putting up a stacked block retaining wall (6x17x12") blocks.
25 ft long, 7 courses, 42" high.
It's going up against an embankment of geotextile layers.
The lower 3 geotextile lifts are (very) sandy soil.
The dark layer is sandy topsoil.
Inn the end I'll just slope soil down to the 42" top of the wall.

Do I need tiebacks to the wall blocks?
Can I backfill it with sand?
You can see a test-stack of 7 blocks.
View attachment 2423010

I have built many bulkhead. I don't think this will hold the way you are doing it. The best way is to either use plastic sheet piling or do concrete telephone poles stepped back as you go up pinned with 3/4" rebar every 30".
Plastic sheets will require a tieback system 25' from the wall. You will also need to put filter cloth behind the bulkhead.

 

[AnotherBueller]

Your geotextile looks impressive!!!

The main reason for retaining walls to fail is water building up behind them. The water creates pressure, adds weight and loosens the soil. Another issue is when there is water behind the wall and the ground freezes. The ground expands and moves the wall. When the ground thaws, the wall remains in the moved location and either fails or is a lot weaker.

A drainage pipe at the bottom solves a lot of future issues. Rock is used between the soil and the wall so water will drain to the bottom and then exit through the pipe. Weep holes do this for smaller walls, but it's not as effective as a perforated pipe. Remember, the holes for the pipe go on the bottom.

Anything up to 4 feet tall generally doesn't need any engineering. Just stack them and be done.

Usually, the first row is buried in the ground to lock the entire wall in place.

I looked into doing this type wall (40W X 4H) by my shed. When I priced it out and added in the amount of manual labor I would need to do - - I went with Lego blocks from a local concrete place, made of non-continuous pour left overs at about 1,500 lbs each and $300 per block. All said and done cheaper, quicker and much easier on my 74 year old back.

 

[aircommuter]

Do you have a cross section drawing of the existing geotex you can post? Were the layers of compacted material tested? Sand isn’t a good fill for that purpose. Sand fill works best in a trench where it’s trapped and can be compacted and it stays in place. What will the slope be above the proposed wall?

 

[Sodo]

Impervious plug at the top is a must as you don’t want to introduce surface water to a subsurface drainage system.

Got "claylike" soil as a top layer. Currently it drains away from this wall. Fingers crossed that it will continue to drain "away"as the whole stackup settles over time. I will have to pay attention over the years and deal with it.
This is not like an engineering job that a responsible party signed "responsible" then has to come fix it if it doesn't work.
It's mine and I live here.
I will have to pay attention over the years and deal with any problems.
I think the main focus will be ensuring water goes the other direction, doesn't dump over the edge to get behind the wall.

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.

I chose the fabric based on availability and price.
I had to pay $400 for a 600 ft roll. Which I thought was cheap.
I got it from a guy who bought it as surplus (for a song).
It has no current pedigree (purchase invoice etc).
It's "Huesker Fortrac20".

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.

In the 7 years I've lived here I don't see any water problems in this area.
I'm capturing all the water that I can (downspout and driveway) tight drainpipes.

Seems like you may need to backup a bit in this project.

Can't do that.
I need to get the best info that I can and move forward.
This project can't sit or it won't get done 'till next winter and my wife aint havin that.
She wants it landscaped and growing cover ----->this spring.
And I agree, I want it looking like it was "existing" and ASAP.

Tomorrow an experienced wall builder is coming to help.
He's not a contractor, he's a laborer but he's done some pretty wild projects.
Young guy recommended to me by a 'driveway contractor'.

Here's a pic I took of a freeway overpass construction that I took while driving by.
Absolutely _Vertical_ layup of geogrid. Appx 22 lifts, maybe 18-24" each.
I'm guessing they will assemble a veneer of concrete panels over it.

 

[Sodo]

Were the layers of compacted material tested? Sand isn’t a good fill for that purpose. Sand fill works best in a trench where it’s trapped and can be compacted and it stays in place.

There is no test.
Compaction is just what I can do with the excavator track.
Sometimes I was able to use the tractor with a full bucket load and its small diameter front wheels.
The sand has a little 'dirt' in it and packs very nicely.
And it's winter, and has a bit of water in it.
I expect that it will settle (drop) over time, but probably not as much as dirt.

The guys who brought it told me that it was similar to what the city used for roadbeds.
It was all free, and delivered for free too. Many 11yd truckloads.

Do you have a cross section drawing of the existing geotex you can post?

Here's the first 8 lifts.
No fill dirt dumped over the fabric (yet) in this pic.
There's a lower level 8 foot long retaining wall (48" high) too.

The 9th lift is the "claylike layer" ontop.
The noses of the geotex fabric is covered by fill-dirt dumped over the side.
It has to have dirt covering it - because any water running over it will scour the sand out of the geo-tex layers quickly.
The final dirt layer will be dark topsoil so vegetation will grow on it.

What will the slope be above the proposed wall?

This final slope of the 'dirt bank' will be topsoil.
I suppose it will be a little shallower than 1:1.

Hope this answers some of your GREAT questions!
Definitely appreciate experience looking over my shoulder.

I know this is not the engineering way.
I definitely appreciate the engineering way, and there's a place for it, and its responsibility
but this is on the "git'er done program".

 

[FullMetalBucket]

Lots of good info in this thread. Looks like I will be joining the wall building club. Our “new” place we moved to has a retaining wall on one side of the property line that’s about 55 feel long. It starts at 5 feet high and goes down to 2’ heading to the back of the property. The current wall was just stacked rocks and it finally collapsing. No idea how old it is. Cheapest quote to rebuild was 22 thousand, and that’s reusing the existing rocks. So yeah I will be following this for sure.