Thread: How would you prepare a base/foundation for filtration in this situation?

This isn't really a pond construction question as such, hence posting here.

As most will know the house I moved into already had a very old pond which I recommissioned last year as shown in my build thread.

This is how the pond and rockery behind it looked when I'd finished, and as a cost saving temporary solution the skimmer line was pumped over a fibreglass/foam type waterfall as seen on the right hand side:





The area behind the pond between the pergola posts is a boxed in with scaffold poles and concrete posts concreted into the ground with gravel boards slotted in, then the entire area has been filled in with soil. The section of pond in this area is only single skin blockwork with the soil acting as the back fill.

I've now removed the waterfall and most of the rockery to create space to install a Bead filter which will feed a protein shower.







From another angle this is the entire area and you can see the weight of it all is taking its toll on the gravel board rear wall which is still very solid but has tilted. I don't think there's much I can do about this other than reinforce it further as is:

some people would have an egg about not being flat laid blocks or double skinned brick thick,
but i think a lot of ponds in the UK are over engineered unless you want them to last for 100 years.
then again when building from new most aren't bricklayers or builders so a bit of overbuild gives some security.

as for your conundrum mate it's a bit of a difficult one.
i think the single skin is ok supported by the full weight of soil, but couldn't say what would happen if you excavate the area where you want to put the bead...
but if that retaining wall doesn't hold it firm against the single skin, it could lead to problems as it's a long straight run...have you noticed any movement since you have been there?
ie it has obviously moved, but has it stopped moving?

I'd be inclined to either shore up the retaining wall with a new reinforced concrete retaining wall and remove the gravel boards and back fill.
or drop the water level in the pond and build a second skin tied into the single to give it all the strength it could need....
and you can lose the rockery and build what you like behind it then and potentially give you room for a bigger filter area/house.

i wouldn't build or slab anything load bearing on top of buried pipework, that could open a completely new can of worms...

i know that place is good as it's next to the filter house, but is there room to the left side of the rockery area to put a bead,
more pipework, but less hassle with disturbing something?

The pipework is yours so no leglisative issues.
If it's just a couple of returns (50mm?) and you are worried about soil heave and fracturing pipes I can think of several possible ways round this. If you are uncertain about ground compaction/stability I can immediately think of a way to get what you want. Run the high quality smooth walled Oase 50mm flexible pipe through 110mm sewer pipes. Will be protected against sharp edges, will flex rather than split, should never leak (unless your pond falls into a sink hole) and can be pulled through and out if any other issues, blockages, etc. Not saying this is the best answer, but it's one way

Originally Posted by RS2OOO

This location is the only option really Dave.

As for the buried pipework, it is just for 2 mid level returns and for the skimmer line (which in itself is buried along the edge of the pond so any base can avoid that).

For the mid level returns I could dig down to them and sleeve them etc which will protect them from forces, but would obviously still be a nightmare if one ever did spring a leak, unless I avoid a concrete slab and just tamp down the soil and then type 1 over the top.

I don't want to start digging and upsetting the ground just yet until I've determined how best to move forward.

One option I did think of was to sledge hammer down scaffold poles as deep as I could then install boards over the top as a level base for the bead filter, but even scaffold poles, boards and fittings are expensive now.

the only thing about hammering scaffold poles in, is they would continue to sink under load especially when the ground is wet.
you would need to dig out holes to put concrete in to give them some support like you do with pergola posts ect...

it might even work as you say, just building over it a bead wouldn't be too heavy. but would add load to the retaining structure.
depends on how well compacted or supported the underground pipes are...but a risk you would have to decide.
i can't think of an easy 100% safe way to do it other than new pond wall or retaining wall...

Hi Steve,

how far below the surface are the return pipes ? i think i would be inclined to lose most of the rocks or at least enough rocks that would replicate the weight of a filled bead so not to add anymore stress to the fence etc, i would then buy an oversized metal plate (like what you see on the roads to cover holes at roadworks and simply lay that on the ground for the bead to sit upon this would help support the bead and spread the weight, no need for the faff of foundations or brick work for the bead to sit on, main problem will be trying to locate a metal plate but sure ebay/faebook mkt place or a reclaimers yard will have something suitable.... could you not install the bead at the opposite end of the rockery and submerge into the ground? (unsure how they work do they have to be above pond level) ? assuming the other end does not have return pipes or anything??

Not sure I can be much help here Rs.
Not familiar with a bead filter,what height are they?
As Dave said if the rear pond wall is only single skin I would be digging down and building a 4ins breeze block supporting wall which could also support the shower.

Bead could then go outside of the new wall.

On my old liner pond years ago I made a pond retaining wall from pieces of an old sectional garage wall which is reinforced with rebar and that never moved.
Not much help Steve but good luck with it.

Sounds ok Steve, what is the pipe going along the pond wall under the soil in the diagram,skimmer pipe?

Could that be moved and move the soil from the pond wall and fill with concrete or ballast be more stronger.
Just I thought the soil could heave a bit if your worried about the pond wall strength.

Dont want anything to happen same as your sleeper in your last house mate.
Even if you remove the soil and rammed in those stones from the waterfall,could do it in stages if your worried of it collapsing.

Originally Posted by john1

Sounds ok Steve, what is the pipe going along the pond wall under the soil in the diagram,skimmer pipe?

Could that be moved and move the soil from the pond wall and fill with concrete or ballast be more stronger.
Just I thought the soil could heave a bit if your worried about the pond wall strength.

Dont want anything to happen same as your sleeper in your last house mate.
Even if you remove the soil and rammed in those stones from the waterfall,could do it in stages if your worried of it collapsing.

Hi John,
Yes the pipe along the pond wall is the skimmer line.
The other 2 are the mid level returns. One of them turns 90 degrees and through the pond wall below where the shower will be placed, and the other runs all the way to the far end of the pond and I assume has a section that runs in the concrete between the 2 pond skins.

The pond, or at least this part was built over 20 years ago so has certainly stood the test of time. The filter pit was tied to the pond and had broken away and sunk.

When I stripped off the old fibreglass there was absolutely no indication of any movement of any pond wall. The rendered blockwork looked perfect everywhere as can be seen here (obviously some chunks of render came off as I ripped off the old fibreglass, but structurally it was sound):





The surprising thing is, the entire pond is double skinned AND has concrete poured between the skins, yet the part that was back filled with soil was strangely left single skinned with no additional support. It seems odd to over engineer everything to overkill, then completely not bother on one section. This image gives a good overview:





Those stones in the rockery are extremely heavy, it took 2 of us to lift the larger ones, then on the 3 or 4 really large ones we couldn't lift them at all, we had to both get one end and roll them. They will definitely be handy as support, just moving them isn't easy.

It would be comforting to reinforce that pond wall and its a job I'd like to do, but I really want to avoid emptying the pond if I can, so the aim is just to find a way to securely place the bead filter and shower without it sinking or moving, and just leave the pond wall as it is nicely back filled with soil.

The remaining raised space behind the pond will still be used as a rockery or for plants etc. If I was building from scratch I would definitely have made it into a storage bunker with soil and plants on top to make best use of the space.

The total footprint of the bead filter inc. pipework is 90cm x 60cm and about 80cm high. The shower will go infront of it (on the pond wall) and has a foot print of 80cm x 45cm including the weir.

Can see it more clearly now Steve the skimmer being on the single wall,
If you could roll some of them boulders against the wall would help.

How you getting on with the renovation Steve?

Top man Steve good job there, get it all up and running now.

very neat and tidy job

looks like you got it done just in time too... some wet weather forecast next week.

Originally Posted by davethefish1

very neat and tidy job

looks like you got it done just in time too... some wet weather forecast next week.

But the easter mega heat wave should help out !! (Apparently!!!!)

Sent from my SM-G973F using Tapatalk

Originally Posted by Ajm

But the easter mega heat wave should help out !! (Apparently!!!!)

Sent from my SM-G973F using Tapatalk

Could do with that Johnathan,pond temp stuck at 9.5 now.