CW's Back Yard Water Garden Begins!

[GBBUDD]

Probably

 

[combatwombat]

Well, this retaining wall idea has turned into a real boondoggle. Digging out the old drain tile & rock for the wall footing has caused a few partial shelf collapses that will have to be rebuilt. There's no reasonable way to dig out all the rock, so some of it is going to have to stay. I've overdug everything so that I can cover w/ sand, but what pain in the ass this has been. And rain is coming on Saturday, so I've got to get at least the underlayment back in before that.

I sure hope this ends up being worth it!

I could also use sanity check on my retaining wall plan:

1. Tamp soil in wall footing trench.
2. Place lots of layers of underlayment over soil in retaining wall footing area.
3. Place liner.
4. Place lots of layers of underlayment over liner in footing area.
5. Place 6" of paver base and tamp (needs to be angular gravel to provide a sure footing for the wall).
6. Wrap the paver base in a few layers of underlayment or scrap liner.
7. Lay a thin layer sand to level the block wall base.
8. Lay the wall.

Now, it comes to backfilling the wall—especially the collapsed areas. Wondering if I should do this inside or outside the liner?

Inside the liner is easy but requires hauling a bunch of extra gravel, and needs to be rounded gravel, which doesn't compact well.

Outside the liner, I can reuse the soil from the collapses or replace with angular gravel, which will compact really well to better reinforce the dirt behind it and also provide drainage to bottom of wall for any water that ends up down there. More like a traditional retaining wall. Would be a total pain in the ass because I would have to fold up the liner and add a bunch more underlayment in that area.

Hmm... choices. Usually the hard way leads to better long term results. I'm pretty exhausted, though.

 

[brokensword]

Well, this retaining wall idea has turned into a real boondoggle. Digging out the old drain tile & rock for the wall footing has caused a few partial shelf collapses that will have to be rebuilt. There's no reasonable way to dig out all the rock, so some of it is going to have to stay. I've overdug everything so that I can cover w/ sand, but what pain in the ass this has been. And rain is coming on Saturday, so I've got to get at least the underlayment back in before that.

I sure hope this ends up being worth it!

I could also use sanity check on my retaining wall plan:

1. Tamp soil in wall footing trench.
2. Place lots of layers of underlayment over soil in retaining wall footing area.
3. Place liner.
4. Place lots of layers of underlayment over liner in footing area.
5. Place 6" of paver base and tamp (needs to be angular gravel to provide a sure footing for the wall).
6. Wrap the paver base in a few layers of underlayment or scrap liner.
7. Lay a thin layer sand to level the block wall base.
8. Lay the wall.

Now, it comes to backfilling the wall—especially the collapsed areas. Wondering if I should do this inside or outside the liner?

Inside the liner is easy but requires hauling a bunch of extra gravel, and needs to be rounded gravel, which doesn't compact well.

Outside the liner, I can reuse the soil from the collapses or replace with angular gravel, which will compact really well to better reinforce the dirt behind it and also provide drainage to bottom of wall for any water that ends up down there. More like a traditional retaining wall. Would be a total pain in the ass because I would have to fold up the liner and add a bunch more underlayment in that area.

Hmm... choices. Usually the hard way leads to better long term results. I'm pretty exhausted, though.


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If I'm reading you corrrectly, you're going to put 'angular' gravel INSIDE the pond, atop the liner, right? IMO, you're asking for trouble, espeically if you're going to compact it. I know HDRPE is tough but I'd not risk it. Refresh my memory; this is the base of your stacked rock wall? Why not just put down several layers of the HDRPE as underlayment and use solid concrete blocks? Any sharpness will be mostly pointed away from your liner and with the extra underlayer, should nullify that. Plus, the blocks are built for compression, which is what you're going to have stacked on top.

You could also lay the blocks in sand, to help with any leveling issues. I think I mentioned I used stacked rock as facia for my bog and just dug out a shelf to put it on, and I used solid slabs as my base, without any additional underlayment other than the liner itself. No issues, but mine is only 2' below surface level and 12" above.

Just an idea.

 

[GBBUDD]

you're going to put 'angular' gravel INSIDE the pond, atop the liner, right? IMO, you're asking for trouble, AGREED. WHILE YOU ARE building a retaining wall your not. I would dig a trench where the fotting is surrounded on the sides and place fabric liner fabric sand compact the sand place fabric or rubber over the trench which should still be a depression . And the build the wall on the scrap liner or fabric this help lock the sand from getting displaced by the water as it will be locked in.

They suggest angular base to lock in /compact but they also look at draining . You don't have that issue.

 

[combatwombat]

@brokensword & @GBBUDD: I hear those concerns. Makes sense. I guess I don't really understand how you can build a 3' retaining wall w/o a really solid base which, as far as I know, can only be achieved with angular gravel with fines. Compactable stuff. Sand doesn't compact.

You guys really think that encasing a paver base in 3 layers of underlayment (encased on all sides—totally encapsulated) is going to lead to trouble? What about a middle ground of using 1/4" angular + fines? That stuff is practically sand, but compacts really well.

Is there something about the wall being inside the pond and the base being 5' below grade that makes the foundation of the wall less important?

 

[brokensword]

@brokensword & @GBBUDD: I hear those concerns. Makes sense. I guess I don't really understand how you can build a 3' retaining wall w/o a really solid base which, as far as I know, can only be achieved with angular gravel with fines. Compactable stuff. Sand doesn't compact.

You guys really think that encasing a paver base in 3 layers of underlayment (encased on all sides—totally encapsulated) is going to lead to trouble? What about a middle ground of using 1/4" angular + fines? That stuff is practically sand, but compacts really well.

Is there something about the wall being inside the pond and the base being 5' below grade that makes the foundation of the wall less important?

the reason you pour a footing/foundation is to give you a level and solid base upon which to put the wall. In this case, you have a solid base already with the ground. Unless you think building such a wall is going to lean/topple, you're overthinking this. If you want to make sure there's no topple effect, you can tie your stone in perpendicular, above the water line and below your final stack, sort of like they do with 6x6s and wood retaining walls. I just don't see the need, personally; you can always let your wall slightly lean back toward the liner+dirt backing as you build up.

If you build with solids below and use your stack up above, from just below the water level to your final height, you should be good. And like any good masonary wall, you lay these blocks in an overlap method like facia on a house, you don't stack straight up (I'm not going to assume you're versed in masonary techniques; no offense intended if you are). And I'd use the solid slabs/blocks, not the typical 8" two core blocks. If you want better stability, use 12" blocks. I used 8x16x4 slabs but I only had to have one base course. You may have more, depending on your design. I'd NOT stack from your pond bottom, I'd dig a shelf, 12" wide, and 6" below your water line. That's what I did. And in doing so, you minimize the number of blocks and also your facia stack. How high above the water surface are you intending again? How far below?

And you can do the triple layer of extra liner under this block/slab base just as I described above.

The main concern I have is that anything round, won't put any cutting pressure on the liner--angular gravel will. (even then, I'd not put anything other than flat on my pond surface). You're thinking that packing/compression is important but you're already starting with a compressed surface in the base ground of your pond. Here, you're only needing support for your facia rock. If you really want to make it overly strong structurally, do the blocks with holes, take some rerod, bend it into a U shape that spans 2 block openings, and send it down with concrete. Do this for all the holes and your wall will be unified. I'd then do the tie-back with another rerod at the top of your wall every 4 ft. You'd then secure this tie in to something staked into the ground. But, this would be overkill imo. I didn't feel the need to do that, but again, my rock wall is only about 16" high. I don't see the need for your wall stack to be anything more unless you have some artsy vision to your design and want it higher. I don't remember you saying anything like that, I think you're aiming for something like I did.

 

[combatwombat]

@brokensword: Thanks for the details. I think you missed the location/purpose of the wall. I will be using 16L x 12W x 6H landscape retaining wall blocks. This wall is at the bottom of the pond and is fully submerged. There is no practical way to do a tie-back/deadman detail. It is intended to increase the floor area of the deep end of the pond.

 

[brokensword]

@brokensword: Thanks for the details. I think you missed the location/purpose of the wall. I will be using 16L x 12W x 6H landscape retaining wall blocks. This wall is at the bottom of the pond and is fully submerged. There is no practical way to do a tie-back/deadman detail. It is intended to increase the floor area of the deep end of the pond.

so there's a lip on these? They'll then angle backwards slightly, yes? Problem solved; just stack on top of these your facia stone (if I remember right, you're taking a page from Darksaber's pond build? With his stacked stone?

[edit]; just make sure your first course is with the lip either off or up; this would be the 'sharp' edge you don't want pushing into your liner, even with extra liner beneath.

 

[combatwombat]

so there's a lip on these? They'll then angle backwards slightly, yes?

Yep.

if I remember right, you're taking a page from Darksaber's pond build?

Yes, exactly. To be honest, though, the construction detail on that pond makes me nervous. If it were above ground and not in a pond I'm pretty sure there is no way it would be up to code. Maybe Aquascape has engineering for those things that I don't know about.

My wall probably wouldn't meet code either, though, as you're technically supposed to get a permit + engineering for anything over 4'. And you're not allowed to stair step walls like both mine will and Darksaber's does unless you set your upper wall back at least 2x horizontally the height of the first wall. Mine will be 4.5' vertical with a "stair step." 3' of retaining wall @ bottom of pond + 18" of top shelf with typical medium sized boulder wall.

I have extremely free-draining soil and am building under the max height allowed for the block used, so I feel good about the strength of the wall.

But, you know, I'm not a civil engineer, so maybe I'm missing details about how building over a liner underground is not subject to the same types of forces as an above ground wall. At the end of the day, though, they're both doing the same thing—retaining soil at a slope that it would not do naturally. And dirt can push pretty hard.

I am definitely not going to set any 2000+ lbs boulders on the ledge above that wall, though.

 

[brokensword]

you also have to realize that in this case, as opposed to above ground, you have the force of the water pushing back. I did the calculations once and it was a ton, literally. If you hadn't planned on this wall, you'd be looking at the water to hold it's shape against all sides, right? And many a pond is dug fairly straight sides down, and you don't hear about many collapses (though, I do recall hearing its best to slope the sides back if your pond is going much deeper than 5' (I think). So in your case, you have two factors working in your favor; natural water force and now, retaining wall force, both acting to hold that side as is. And stacking rock on top just gives you more of that. The only issue in my mind would be the height and possible toppling, hence the tie back of above reply. Do you HAVE to go that tall with your wall? That's why I suggested you dig a shelf and stack on the earth, esp since your visible stack is only 18". It would mean a lot less work, blocks, worry? A pic of mine, below, for your reference.

 

[combatwombat]

Liner is back in! Just in time for the rain that started last night. I was able to reposition it so that I can now get the pond, the wetland filter, the intake bay AND the waterfall with no seams.

Liner was way too big whenI started and is now about the perfect size. Funny how that works out.

Moving a 40x70 liner around with tons of curves and shelves is really difficult!

The only issue in my mind would be the height and possible toppling, hence the tie back of above reply. Do you HAVE to go that tall with your wall? That's why I suggested you dig a shelf and stack on the earth, esp since your visible stack is only 18". It would mean a lot less work, blocks, worry?

I think we’re talking about different scenarios still. I’ll have to draw a picture to illustrate. Also, the entire pond is getting rocked, so weather it’s retaining wall blocks or boulders, would be a similar amount of materials.

 

[combatwombat]

@brokensword: this is the profile of one side of the pond where the wall will be. Best I could do chasing a toddler around on no coffee!

 

[brokensword]

@brokensword: this is the profile of one side of the pond where the wall will be. Best I could do chasing a toddler around on no coffee!

View attachment 138239

okay, so I got the picture now. So you're putting up this wall ONLY to create more swimming area? The wall is not going to be recognizable once it gets covered with algae; imo, why not just do without and have a liner wall there? Are you worried the wall might collapse in without the weight? Or are you just trying to mimic the surrounding walls with 'thinner' profile rock? I don't see in your drawing the stacked rock scenario, unless the 'wall' IS the stacked rock? Then where are the landscape blocks? I made an assumption you were trying for support below, visual stacked rock above.

 

[combatwombat]

So you're putting up this wall ONLY to create more swimming area?

Yep.

why not just do without and have a liner wall there? Are you worried the wall might collapse in without the weight?

Exactly. Bottom 2’ of pond is basically sand. Wall will not hold up long term without retention.

I chose a block wall for this location because it will not be visible from most viewing angles and engineered blocks take up less space than the boulders I would want to use to stabilize a 3’ wall in these soil conditions.

Also, I just don’t want any visible/accessible liner.

 

[brokensword]

Yep.




Exactly. Bottom 2’ of pond is basically sand. Wall will not hold up long term without retention.

I chose a block wall for this location because it will not be visible from most viewing angles and engineered blocks take up less space than the boulders I would want to use to stabilize a 3’ wall in these soil conditions.

Also, I just don’t want any visible/accessible liner.

gotcha; sorry for dragging this out as I was totally oblivious, apparently, to your purpose with the wall. Somehow, I thought you were going for narrower but with above water visual appeal ala Darksaber's build.