Oversized Hole...

GreeBo · 12-05-2025 09:52AM #1

So, a fun one for you all.

As part of house renovations I had my builder dig a hole it the garden for an in-ground trampoline.

Went to install it over the weekend and it turns out that the hole is significantly oversized in one of the dimensions

Trampoline is 4.1M x 2.5M and the hole is supposed to be the same with a shelf for the frame to sit on (as below)

However the hole is a good 0.5m wider than it should be, meaning that the frame on one side totally is hanging in mid air.

I can't see an option here that doesn't involve me either totally relocating the trampoline somewhere else in the garden and hiring a mini digger, or trying to build some sort of ring foundation on concrete with shuttering etc. to use the existing hole.

I'm worried that this might not be possible since its going to be hard to create a foundation that wont just crack and fall into the hole unless I am throwing in some rebar and maybe driving piles…

All of which is a royal PITA for a bloody trampoline!

Help?

The Continental Op · 12-05-2025 01:24PM

Easyish option I can think of is to hunt around the neighborhood for a "dead" trampoline. Then take the legs off it and use it on yours. You might need to dig the hole a little be more around the edges for the legs.

Edit> You could also cut the legs down a bit to save on digging. But does all assume that you have sockets on the frame to put the legs into?

GreeBo · 12-05-2025 03:36PM

https://www.boards.ie/discussion/comment/123440365#Comment_123440365

Cheers for ideas, its a specific frame for in ground installation, so without welding I don't see any legs option being possible, but even still, I think the problem there is that I will still be left with the gap on 1 side (over a ~1M hole…)

Its a but painful as any type of frame/structure that you would normally build will just be in the way when the sheet deflects…

I think I see some serious tamping in my future!

If it was flat I could get a whacker plate maybe, but dont fancy that on a 60* slope…

The Continental Op · 12-05-2025 03:38PM

Sandbags? If you are anywhere near Waterford I can give you 50 coal sacks to use.

GreeBo · 12-05-2025 03:40PM

https://www.boards.ie/discussion/comment/123440830#Comment_123440830

Hmmmm, interesting!

Maybe sandbags as a sloped retaining wall type of thing…possibly with a few lengths of rebar driven into the ground (which is heavy clay after the first 50cm!?

Let me ponder that one for a bit…thanks again!

#GetTheProfessionalsInSheSays

baxterooneydoody · 12-05-2025 03:49PM

A 4x4 timber post bridging the side where the frame is, dig it in either side for the frame to sit level and fill it up with soil

raxy · 12-05-2025 03:51PM

how long ago was the builder there? They might come back & fill it in for you?

Allinall · 12-05-2025 03:51PM

No idea on your problem, OP, just very thankful you didn't post in the "Personal Issues" forum.

GreeBo · 12-05-2025 03:57PM

https://www.boards.ie/discussion/comment/123440871#Comment_123440871

Interesting, build an external frame out of 4x4 maybe with a leg in the middle of each span, I can then use that to level and control the height of the whole thing….

Though it does mean I will have a bunch of 4x4s quite close to the surface of my (soon to be) lovely green lawn and also timber buried in soil….so not sure how long they would last?

dammit, if I have to get a metal frame for my metal frame I will not be happy! :(

baxterooneydoody · 12-05-2025 04:12PM

https://www.boards.ie/discussion/comment/123440905#Comment_123440905

Treated 4x4 will last for years, the kids will have long since finished playing with it by the time the timber gives up

The Continental Op · 12-05-2025 04:43PM

https://www.boards.ie/discussion/comment/123440945#Comment_123440945

It will have ripped well before the timber rots.

Its UV that kills them in the end. They last longer if you can keep a cover on them when not in use.

GreeBo · 12-05-2025 06:51PM

https://www.boards.ie/discussion/comment/123441046#Comment_123441046

I hope you are not disparaging the fine warranty that my good friends in Berg (say they) provide! :)

Yeah its a fair point, I'm probably more "worried" about having the 4x4 so close to the grass surface, but not the end of the world if there is a little browning for a few weeks during summer I suppose.

Lay them onto compacted dirt or lash a bit of hardcore in for drainage? Probably not much point in only drainage underneath if they are under 6 inches of dirt...suppose I can burrito them in some gravel.

#overthinking

Lumen · 13-05-2025 08:07AM

Is the hole oversized on the long side or the short side?

Surely you "just" need to move soil from the bottom of the hole to the side? As long as the slope isn't too steep it should stay put as it's heavy clay.

Wouldn't bother too much with tamping, just make it higher, few stomps and let the kids bounce it to compaction.

If necessary infill the void in the bottom with fresh soil. A couple of jumbo bags will do it.

Captain Hindsight says if you'd done this in March you could have sown grass in the hole to aid soil stabilisation 😀

GreeBo · 13-05-2025 01:09PM

https://www.boards.ie/discussion/comment/123442724#Comment_123442724

But of course its on the long side! Thinking back, they originally dug it perpendicular to the desired direction, so I am dealing with infill already (thats loose and actually badly dipped already)

Slope is pretty slopey tbh, 60+ degrees.

I think I'm going to rent a micro digger, use that to flatten the humps in the rest of the garden prior to rotovator action and use any excess to "rebuild" the hole dimensions. Hoping I can use the bucket to compress the top/sides to be a bit more stable.

wildwillow · 13-05-2025 01:13PM

I had exactly the same problem and the easiest solution in the end was to dig a new hole and back fill the existing one. Thought of lots of solutions, most were unsatisfactory and expensive.

GreeBo · 13-05-2025 01:22PM

https://www.boards.ie/discussion/comment/123443702#Comment_123443702

Yeah this is exactly my fear, the installation instructions specifically advise you to assemble the frame before digging, but the lads were on site with a mini digger and the trampoline was still in transit…

Did you backfill and then re-excavate "properly" or just continue with the new location?

raxy · 13-05-2025 03:21PM

A lawn roller would be handy for levelling & compacting the soil.

https://www.chadwicks.ie/garden-roller-roll-garden-roller-roll-garden-roller-roll.html?srsltid=AfmBOoo7yAg2yP-U4OOAX1zYBPrF2RrHnqNIMM0rEDCyfLF-JKmT-GlE

I have 1 from putting in artificial grass if you're anywhere near Clondalkin.

wildwillow · 13-05-2025 03:47PM

https://www.boards.ie/discussion/comment/123443722#Comment_123443722

New location entirely. filled the old hole with the soil dug out. The edges need to be very firm so, unless you reinforce the edges you are never going to be able to use the one you've dug.

Lumen · 13-05-2025 03:51PM

https://www.boards.ie/discussion/comment/123444243#Comment_123444243

It is possible. You could probably do DIY soil stablisation using cement or lime. They're building houses on this stuff down the road from me.

GreeBo · 13-05-2025 04:59PM

https://www.boards.ie/discussion/comment/123444243#Comment_123444243

3 out of the 4 sides are fine I reckon, but I might be half tempted to put the steel frame on top of a 1x4 or something, but to be honest the contact area of the frame is very large, so its probably overkill, though would help with levels.

I think I will go down the micro digger approach, if that fails I can always use it to dig a new hole.

(or as my wife puts it, "you just want to play on a digger"…..)

GreeBo · 13-05-2025 05:02PM

https://www.boards.ie/discussion/comment/123444258#Comment_123444258

I did see yer man from ProperDIY make some footings out of soil and cement, nothing structural, but just for landscaping bases "Cement Structuralised Soil" he was calling it (as a civil engineer)

The clay is too deep for the support shelf, but once you get to it, its bloody clay all the way down (gave up after 4M when building a soakaway, after 2M the water is coming up out of the ground :()

chooseusername · 13-05-2025 08:34PM

https://www.boards.ie/discussion/comment/123444475#Comment_123444475

"3 out of the 4 sides are fine I reckon,"

So they didn't even check the diagonals for squareness.

GreeBo · 14-05-2025 10:34AM

https://www.boards.ie/discussion/comment/123445154#Comment_123445154

Its square, just over sized, i.e. its 3x3 instead of 3x2.5.

By 3 out of 4 I mean 3 sides of the frame are well supported, the other is floating over the hole :(

Lumen · 14-05-2025 01:44PM

https://www.boards.ie/discussion/comment/123446703#Comment_123446703

By my maths that means you have 1.5m3 of material to put back if you maintain the slope, which is about 15-20 wheelbarrows.

That's two tonne bags of gravel mix and a few bags of cement. 150 euro of materials?

GreeBo · 14-05-2025 04:33PM

https://www.boards.ie/discussion/comment/123447316#Comment_123447316

Well I was a bit loose on the numbers for demonstrative purposes, but its probably close enough!

I reckon I will have at least that in top soil/clay when I level out the rock nursery that was left where my lawn used to be.
I need to get a couple of tonne bags of top soil and sand anyway.

The concern was more on the stabilization side, but if I can compact as I go with the mini/micro digger and shallow out the slope, (which will of course mean more fill, I don't think it needs to be as steep as it is) I reckon I will be ok.

Lumen · 14-05-2025 04:51PM

https://www.boards.ie/discussion/comment/123447928#Comment_123447928

Lower slope will help, but I think you just need the stability where the frame sits, that's where I'd add the cement/lime and then use soil or whatever for the infill.

eusap · 15-05-2025 03:45PM

Can you not build a frame out of Deck Joists and have a small deck around the trampoline?

GreeBo · 16-05-2025 11:36AM

https://www.boards.ie/discussion/comment/123451135#Comment_123451135

I could, but that somewhat defeats the point of having it sunk into the ground and also would be more dangerous (landing on a deck vs landing on grass) so I would have to look into padding etc.

Also I'm then into footings etc. for the deck…

Oversized Hole...

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