Who knows about stacked-block retaining walls?

[Sodo]

WOW some real attention! Thank you.
Not that I didn't appreciate the earlier responses, I'm taking it all in.

Water is it biggest enemy on a retaining wall.
Lots of good advice in comments which you seem to want to disregard.

Hold on there fella the pics above are still current.
Nothing more has been done. Still gathering info.

This level area where the mini-ex and tractor sit does NOT gather water from acres uphill.
It's about 400 sqft of levelish surface that can only collect water from it's own 400SF.
The levelish (new) surface drains ------> away from the wall.
I am concerned that with settling, some of this 400sf could begin to drain towards the wall, that would change things a little.
I haven't considered the 400SF as "a lot of water" risk. I have doubts that it will create a mud-pressure behind the wall.

My advice is to try to have your top ground layers made with clay that slows the water absorbsion somewhat.

The top layer (behind the 4x12 wood) is clay-ish. Water is currently pooling ontop and takes days to go away.
The geotextile layers that you see are filled with sand.
If I use clean gravel as backfill behind the wall, I'm pretty sure it can get down to drains below.

A driveway drainage problem could feed it with driveway water.
Pretty sure I can build a reliable method to prevent driveway water from the 400SF.

Driveway water (and one gutter) goes into that white 4" pipe, and exits far beyond the wall.
If the white pipe plugs up, the overflow will be chosen to go on down the driveway, not to this wall.

The house basement wall is stout, 6" thick concrete wall. 8 feet tall. The paver walkway, if shoved by retaining wall blocks, will be pushing 3 ft above basement floor.

OK that's addressing some of the concerns. I'll get thru them all.

 

[lifedata]

I'm thinking you should put some kind of drain close to the bottom. They make "thin" rectangular drains for tight spaces. JDrain is one brand.

 

[Sodo]

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.

Hardest thing .....

As the saying (might) go...
The best time to (remove) a tree (next to the house) was 30 years ago.
The second best time is "today".

I am gonna punt on this one. They're huge.
Gonna build the wall, and punt on the trees.
I think they're liable to get bigger.

The one 11 feet from the house is 40 inches diameter. The farther tree is 34inches.
Redwoods, planted 40 years ago.
You old farts may need to be reminded that 40 years ago was 1985.

On your wall I think you should excavate more so you have room for drainage pipe (6" clear behind the wall would be enough to get a wrapped pipe in there buried in crushed rock
......
If the additional excavation is not an option you could also move the wall forward 6". Probably wouldn't notice.

Don't wanna cut my geotextile 'cuz the fill could squirt out and push on the wall.

I first planned to build the wall with 8" wide blocks,
but then decided 12" wide would be better,
THEN 12" at a good price came available,
so I lost 4" on the bottom course.

I think a drain 2 courses up will be good enough.
Maybe add a 1 1/2" drain at the bottom too.... why not?

The engineers here can correct me if I'm wrong but to me it looks like the way you're doing it, essentially the geo grid dirt bundles are your retaining structure and the blocks are a going to be the second line of defense, albeit with a couple asterisks.

The concern about the patio pushing against the foundation of your house is also something to think about if you're relying on that to keep your wall in place. That's more math than I can do counting on my fingers.

I thought that a geo-textile layup IS the retaining wall - it's about 6 feet thick.
Where the stacked blocks are mostly a "facing".
Where most of the job of the stacked blocks .... is to hold up the backfill (between the blocks and the geotextile).

It would be great if some engineers with Geotextile experience would weigh in.

 

[jigs_n_fixtures]

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.

I've seen them in engineered walls of over twenty feet. But, that required tiebacks.

 

[jigs_n_fixtures]

There are walls like that, question is how good is the compaction as it is built. There is also a wall like that known as Hilfiker which is wire. He is putting a wall over a wall. Probably should have started differently way before now. I agree about the trees they should also have been removed long ago. Sorry.

Backfill is clean granular material, which falls in at 100% compaction. And is free draining, with enough pore space to allow any retained water to freeze in the pores.

 

[Sodo]

yes free draining. Sand would not be free draining.
I highly doubt there's enough water to soak the sand, (but "famous last words....")
And we don't freeze that hard here.
But I'll use clean gravel, not sand (I have lots of sand nearby).

 

[jigs_n_fixtures]

Ok, reading through this, I have the following comments:

For backfill, see if you can get reject intermediate concrete aggregate from a local Redi-Mix supplier. Some have it, some don't, but it is a suitable backfill which is relatively inexpensive if they have it. Back fill as you go. Don't have more than a couple of courses in the air before you backfill. If you have a concrete stinger, it would be a good idea to run it along your backfill, but it isn't critical.

Drainage: I have seen a perforated poly drainage pipe which was 1-1/2-inch diameter. But, have no idea where to buy it. I try not to specify anything a contractor can't buy through a big box like Home Desperate or Lowers. But they may have it. I've never looked to see. Unless you use a washed aggregate for the backfill, do not install drain lines with a sock filter. The number one cause of failure for drains is fines migrating in and clogging the sock. If you use a good drain material for the backfill, even with the drain line several courses up, the gaps in the un-mortared blocks will weep water through the gaps.

If you install tie backs, do not use rebar. It will rust through, and you will lose the strength. If I had designed the wall, I would have installed geotextile as the tie-back and brought the block up as I installed the geotextile lifts. Not sure of an effective but inexpensive way to tie back at this point. But typically, the block manufacturers don't call for tiebacks until you get to about 8-foot. But that depends on the seismic zone. If your growing redwoods, I'm guessing coastal northern California, as a location. So, seismic could be critical. If I were doing the facing block, I might glue the courses together with one of the high stretch urethane adhesives. Not a good substitute for tiebacks, but will keep the block aligned in most instances, and in reality, if the big one hits, nothing will hold up if your close to the epicenter.

 

[neighborman]

years ago I built some retaining walls using a variety of large rock and mortar they were all over 5' high. The walls that have drainage are still standing after over 40 years.

 

[Sodo]

OK I'm smelling an engineer (or 3)..... Thank you jigs for reading thru! And the other engineers too!
....and the 100-walls experienced 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?

 

[ning]

Hardest thing .....

As the saying (might) go...
The best time to (remove) a tree (next to the house) was 30 years ago.
The second best time is "today".

I am gonna punt on this one. They're huge.
Gonna build the wall, and punt on the trees.
I think they're liable to get bigger.

The one 11 feet from the house is 40 inches diameter. The farther tree is 34inches.
Redwoods, planted 40 years ago.
You old farts may need to be reminded that 40 years ago was 1985.

If those trunks are buried (and it sure looks like it), the death warrant has been signed on the trees.
Good thing is, they'll look fine for a decent number of years. Can't predict how many, though; most likely the water & oxygen uptake from the roots has been reduced substantially as well (burying the trunks results in the trunks rotting out... below grade).

So strongly consider how those trees are going to be taken down at some point, and try to make sure that happens before a storm knocks them down after they've been compromised.