Weep hole question on retaining wall

[oldpops]

Hi folks! First want to say a BIG THANKS to everyone here who has offered advice and suggestions on my questions in the past - I DO APPRECIATE it!

Anyway, a long story short: we have a 35 foot long X 5 foot high section of retaining wall in our back yard that has started to lean on one end, and has some grout cracks and a slight bow starting. I had a company that does tie-backs, and a few companies that can remove and replace the wall come out. The prices for both methods are about the same, and they are both waaaayyyy out of our budget. Just had a structural engineer come out and take a look. he agreed with the wall contractors that the foundation of the wall is fine, and after doing some measurements & calculations (I guess that's what they go to school for) said it is possible to stabilize the wall with some less costly methods. YEAH - finally some good news.

One of the things he said we need to do immediately was to get some weep holes drilled into the wall. I should have asked him more about where and what size to do the weep holes at the time, but I was concentrating on some of the other suggestions he was making (like special braces, pilasters, wing walls, etc.). Anyway, has anyone here had to drill some weep holes in a concrete block retaining wall, or any concrete block wall? I've seen some videos on YouTube and some guys drill a bunch of holes all along the bottom - but I wonder wouldn't doing that weaken the wall ?(causing the wall to fail down there?)

So any and all advice and suggestions on how big of a weep hole to drill, how far above the ground/grade level to drill them, and how far apart to drill the weep holes would be greatly appreciated. I've included some pictures below to get an idea of the retaining wall I'm talking about., Thanks in advance to everyone who offers any help!

 

[larry4406]

I would be inclined to use a 3/8” masonry bit and drill at the bottom of a **** joint where it meets a bed joint. I would do this every 24-36” laterally and around 6-8” above low side grade wherever a bed joint happens to be.

Likely no drainage tile behind but better than nothing.

Drill perpendicular to wall so your drilling only mortar and no block blow out.

You will want a real hammer drill with long bit for this.

 

[Fav Onefour]

You can drill all the holes you want. In the end it's not going to fix the problem by itself. Keep that fact in mind before going through the work of drilling holes.
I get the idea of trying to stop the shifting. It's better than nothing. The wall has signs of a lot of water coming through.

What climate are you fighting? I'm just wondering if you are fighting freeze shifting in the soil or simply warm climate dirt movement? In our cold climate the goal is to basically make the area behind the wall dry. That would take a lot of drainage holes. It also wouldn't really dry the soil behind the wall on it's own.
Do you have sandy or heavy soil? Is there any type of drainage aggregate behind the wall? If you have heavy soils and no other drain systems, it's going to be a tough battle.

The answers to those questions may help a little with advice on drilling holes. @larry4406 , right on with the hammer drill suggestion.
There isn't a simple answer on how many and where. Retaining walls that tall should already have additional retention systems built into them. I'm guessing that one does not. Adding drain holes will not help the strength.

 

[CraigStu]

All the drains I have seen in walls that size are at least 2inches. Usually every 6ft or so.

 

[oldpops]

I should have said we're in southern California. And the builder actually came back years after building the house to put weep holes in the first section of wall. They didn't do the last section because that was done by a previous homeowner. Either way, neither wall had any weep holes

 

[gahrajmahal]

Hello, weep holes are good but you need to control the water making it to the top of your wall. At our house here in Ohio we have about 400 ft. Of stone retaining walls. They range in height from around two ft. up to 10 ft. Tall. Our house is set into a hill and our neighbors have homes above ours and water from rain runs from their property down to ours. After about 25 years here the walls were crumbling and we needed to repair them. First we hired a team of guys to dig down behind the existing wall about a foot down. We lined the ditch with plastic sheet, then ran corrugated pipe with a fabric sock covering that. Then the whole ditch was filled to level with medium pebble stones. At the borders of our property I have also dug drainage trenches so the neighbors runoff goes into the ditch then is diverted away from our property. The beginning is April we had a solid week of rain and the back of our stone walls is soaked I’m sure and no amount of weep holes or French drain is going to stop that. The goal is to divert the water then your wall can dry out. When you need to repair or re-point is when the mortar fails, or in your case the wall bows so much the mortar cracks and fails. With a block wall companies will treat it like a block basement here. They can bore through the block then drive anchors into the soil, sometimes pulling some of the bow out. But to fix it long term the soil needs to be excavated from behind the wall and a new wall is pored behind the bowed section. Sometimes this can be a narrow hole dug down to accomplish this.

 

[oldpops]

Thanks everyone. I always learn a LOT coming here! Not just from my own questions, but when I read the questions of others. There are many posters here who have enormous knowledge and I for one, am grateful for the advice. I think the best thing to do at this point is to save for a new wall. In the interim, I can try a few band-aid solutions to buy me some time, but the final solution is going to be a new wall.

 

[jimy]

If you rebuild this and have the room, I believe the wall will be stronger if there are curves in the design rather than a straight wall.

(But I could be wrong - I’m no expert)

Jim

 

[egdede]

You maybe can fix what was built wrong. If you can trench behind the wall, do that to the base. Drill 2" holes. Lay in weed barrier (pay out for the good-stuff) and pull it up the sides with enough to cover the back fill. Put in a few inches of gravel. Put in a drain tile that has branches to each of the holes you drilled. Finish backfilling with 3/4 gravel to about a foot below grade. Pull the weed barrier over the gravel and top off the gravel with top-soil.

Your wall is just small enough to retrofit proper drainage. You'll be moving a ton of dirt!!! However big you think the pile will be, I bet it will be bigger. I did this in So Cal supervising day laborers from HD. Solved my problems nicely. I wouldn't have wanted to do all the digging (but I'm an old man now : )

Finally, at 5' you are in the danger zone so don't dig a trench so much as a digging the slope back for the top 2'-3', and then dig a 2'-3' deep trench. It makes the back-filling a little complicated because the top gravel wants to spill out. I ended up using plywood to keep the drainage gravel in place while I backfilled the sloped dirt, and then just pulled out the plywood.

 

[Fav Onefour]

The first post mentions the foundation of the wall is fine. Is the wall on a concrete footing?

The method @egdede , mentions is more feasible with a good footing already in place. It would still need tiebacks. The wall might measure five feet but it's holding a lot more than five feet of dirt. All that dirt in the slope above factors into load on the wall. Let's use a height number like six and a half feet to be more realistic. I'm not even sure what is behind the fence? The process of properly repair and adding drainage will require moving a lot of dirt. We're not talking about a shallow narrow trench behind the wall. Probably moving dang close to amount you would do if building a new wall. It better be cheap labor. Every scoop or shovel of dirt will be around or over the current wall. Trenching half way down is doing half the job. Do the whole job right or it's a waste of time.

I'm not trying to discourage the project. I'm just trying to give an accurate expectation of what it takes to do it right.

 

[larry4406]

If you go the new wall route, study deadman and incorporate into the design. Obviously also drainage. If freezing is a concern, consider waterproofing uphill side of wall.

In my area any retaining wall with more than 30” exposure on downhill side requires permit and engineering.

 

[larry4406]

Stacked retaining walls of stepped CMU/split face like units are an option.

 

[oldpops]

WOW! That's a lot of work to do, even if I just hire some day laborers from in front of HD to do the shoveling. I think I may have to go with one of the contractors to remove and replace the wall.

 

[larry4406]

Can you terrace your area so you have several plateaus between neighbors fence and your slab? This would lessen the vertical jumps of each and reduce the wall’s requirements. Also lets you bite away at the project in sections.

Would make for a nice garden in an otherwise useless space.

 

[RyanE]

If you are contemplating complete removal and replacement, consider the use of a GRS (geosynthetic reinforced soil) or a geocell wall instead. Both rely upon the used of layered soil and geo synthetics. The nice thing about their use is you don't need specialized heavy equipment. You could get away with a shovel, wheelbarrow and plate tamper to construct them - no lifting of concrete blocks.

 

[egdede]

I see you said the wall is out of your budget. You can direct something like this..

 

[Fav Onefour]

I have not done geo reinforced slopes. I wonder if that method could hold the wall? It doesn't seem feasible with the amount of dirt and fill behind the wall.

@oldpops , The idea of doing a shovel wheelbarrow project seems feasible if you want a good workout.
The idea @larry4406 , suggested is good. I've done a number of walls with DIY interlocking stack systems. In your case, it would need geogrid tieback layers because of the height. The multi level idea would give you some cool garden space. We have a few of those around my neighborhood.
This is my setup.

Previous owners did the original three tier. The two taller walls each have two layers of geogrid tiebacks.
There are some advantages to block systems. They can be contoured to create an interesting wall. Most of the work can be done as a DIY project.
I did this part of the yard over an entire summer.

With block systems, the base is critical. If you have a footing, that hard part is done. Doing the walls is kinda fun after that point.
The second picture also highlights a key point in the process. I had major slope across my yard that required a lot of fill to level. I used a wheelbarrow and plucked away at the job every night after work. Move as much dirt uphill as possible before building the walls. It took about 140 yards of dirt and fill to level the yard and create base for the patio. I had most on the uphill side before I started stacking block. After completing the walls I needed a few loads of good dirt to top finish. Moving the light dirt over the walls was harder than moving class 5 before walls were in place.

 

[MoonRise]

Weep holes are to allow a place for the up-slope water to get past the wall.

They will do nothing for the weight of the up-slope dirt itself pressing on the wall causing it to bow or lean.

California most likely also has seismic code requirements to account for.

Also check on local building code requirements for height of retaining walls.

Above a certain height (~30" above grade https://www.fencetrac.com/retaining-wall-fence/ ) you are usually required per IBC to have a fence for safety (keeping someone from falling off the wall and getting hurt). And above a slightly higher height (~48" above grade), you are usually required to have stamped engineering plans/drawings or being built to the wall manufacturer's engineered plans using their engineered product to ensure that the wall is safe and sturdy enough so that it doesn't lean or bow or otherwise 'fail'.

YMMV depending on your local code requirements. For instance, Contra Costa County in California flat out says that a retaining wall may not exceed three feet tall https://www.contracosta.ca.gov/FAQ.aspx?QID=246 .

 

[Jackfre]

I‘d definitely core out at least a series of 2” holes. Something you might consider is to go back 5-6’ from the wall, dig sown at least half the height of the wall, and pour a fairly large block. Embed some 1” or so steel rods through the wall with steel gusset plates outside the wall. Once that is done by digging behind the wall you might be able to pull it plumb.